The Geology of Delaware

The Geology of Delaware johncallahan Sat, 06/27/2009 - 00:07
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The Geology of Delaware is an online resource for information about the geology and hydrogeology of Delaware. Although common geologic terminology is used throughout, most information on these pages is explained in general terms. There are many publications available from the Delaware Geological Survey that provide detailed information and the latest research about the geology and hydrogeology of the state. DGS also releases much of the data associated with the publications in digital format. Feel free to browse through these sections to learn more than what is covered in this online book.

How to Use this Book: Each page in this "virtual" book is located inside a chapter. The chapter in which the current pages reside can be identified in two ways: 1) the breadcrumb at the top of the page, labeled "You are here," and 2) the Table of Contents menu at the right of the page, which should be open to the current page.

At the bottom of each page is a small navigation menu. This menu provides links to the previous page (in respect to the page order in the book) at the far left, to the next page at the far right, and up to the current chapter home. The chapter home page lists all pages and sub-chapters contained in that chapter, and is identical to what is displayed in the Table of Contents menu at the left.

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Introduction

Introduction johncallahan Thu, 06/24/2010 - 15:40

A Generalized Geologic Map of Delaware

A Generalized Geologic Map of Delaware johncallahan Fri, 06/25/2010 - 14:15
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This map was created from published 1:100,000-scale geologic maps of New Castle and Kent Counties, and the most current knowledge about the surficial geology of Sussex County. Sussex County was compiled from published 1:24,000-scale geologic maps of various quadrangles and recent fieldwork. (The current version of Sussex County seen here is the same as published in RI76.)

The Delaware Geological Survey (DGS) published the surficial geology of the state of Delaware at a scale of 1:100,000 for New Castle and Kent counties (Ramsey, 2005, 2007). Maps at this scale are useful for viewing general geologic framework on a county-wide basis, determining the geology of watersheds, and recognizing the relationship of geology to county-wide environmental or land-use issues. These maps, when combined with subsurface geologic information, provide a basis for locating water supplies, mapping groundwater recharge areas, and protecting ground and surface water. Geologic maps are also used to identify geologic hazards, such as flood-prone areas, to identify sand and gravel resources, and for supporting state, county, and local land-use planning decisions. Portions of Sussex County have previously been mapped at a scale of 1:24,000. Field work is in progress in eastern Sussex County and will be complete in the near future.

GIS Methods Used to Create this Map

Heads-up digitizing was performed in ArcGIS from maps on which the geologist drew geologic unit boundaries. Geologic unit boundaries are determined through field interpretation of well and borehole data, aerial photographs, as well as contours from LiDAR. Data compilation methods included merging existing geologic attributes (Ramsey, 1993, 2001, and 2003; Andres and Ramsey, 1995; Schenck et al., 2000), clipping polygons to the state boundary, and extracting and merging the swamp/marsh attribute from the USGS National Hydrography Dataset (NHD). Existing geologic digital data and the NHD are both mapped at a scale of 1:24,000. These areas were designed to be viewed at a scale of 1:100,000 (polygons with an area less than 25,000 square meters were deleted). Base map data (not shown) were compiled for geographic location and editing purposes. Datasets included hydrography, transportation and boundaries for the state of Delaware.  Hydrography data were also generalized to a scale of 1:100,000 using the same method for generalizing the geologic data. A few deleted hydrography polygons were reintegrated into the dataset since they connected stream line data.

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Additional Documents
/sites/default/files/geohydro-docs/statewide-de-geology.pdf

A Summary of the Geologic History of Delaware

A Summary of the Geologic History of Delaware johncallahan Sat, 06/27/2009 - 00:01
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The State of Delaware is located within two physiographic provinces, the Appalachian Piedmont and the Atlantic Coastal Plain. Most of the state lies within the Coastal Plain; it is only the hills of northern New Castle County that lie within the Piedmont. Piedmont means foothills. Delaware’s rolling hills, which rise to over 400 feet above sea level, are a part of the foothills of the Appalachian Mountains. The rocks at the surface in the Piedmont are old, deformed, metamorphic rocks that were once buried in the core of an ancient mountain range. This range formed early in a series of tectonic events that built the Appalachians between about 543 and 250 million years ago. During an early event, called the Taconic orogeny, an offshore chain of volcanoes collided with the ancient North American continental margin to push up a gigantic mountain range that was as tall as the Alps or the Rockies of today. Geologists date the Taconic orogeny between 470 and 440 million years ago. The Taconic orogeny is important to our understanding of the geology of Delaware, because during this event, the rocks of Delaware’s Piedmont were deeply buried under miles of overlying rock and metamorphosed by heat from the underlying mantle. Since that time, rivers and streams have carried the erosional products, mostly sand, clay, and gravel, from the mountains onto the Atlantic Coastal Plain and continental shelf. As the mountains wear down, the buried rocks rebound and rise to the surface. Thus what we see in the Piedmont today are old, deformed, metamorphic rocks that were once buried deep within an ancient mountain range.

The oldest rocks in Delaware also preserve the history of an earlier mountain-building event called the Grenville orogeny. This event occurred approximately one billion years ago. Within Delaware’s Piedmont, five distinct rock units can be recognized: (1) rocks of the volcanic arc (Wilmington Complex), (2) rocks formed from the mud and sand deposited in the deep ocean that existed between the volcanic arc and the ancient continental margin (Wissahickon Fm.), (3 & 4) rocks that were once sand and carbonates (calcite and dolomite) lying on the shallow shelf of the ancient continental margin (Setters Fm. and Cockeysville Marble), and (5) rocks of the ancient North American continent (Baltimore Gneiss). The names given to these units indicate the geographic area where they were first identified.

Because of the total absence of fossils, determining the age of the Piedmont rocks has always been difficult. Age must be determined either by correlation with units elsewhere in the Piedmont, or by calculating radiometric ages from measurements of radioactive elements and their decay products (usually uranium-lead).

Fall Line
Delaware’s Piedmont ends at the Fall Line where the metamorphic rocks dip under and disappear beneath the sediments of the Coastal Plain. The Fall Line roughly follows Kirkwood Highway, Route 2, across the state between Newark and Wilmington. Parallel to the Fall Line is a narrow zone where rapids and waterfalls are common. Delaware’s early settlers built near the rapids using the energy generated from the falls to power their mills.

Explorers and sea captains of the colonial period found the bays, rivers, and streams of the Coastal Plain navigable until they reached the fall zone. Here it was necessary to dock their ships, unload the cargo, and move it inland by rail or road. Many of the settlements that grew around these unloading sites later became large cities. Richmond, Washington, Baltimore, Wilmington, and Philadelphia are cities built around ports located along the fall zone.

Atlantic Coastal Plain
Delaware’s Coastal Plain rises to about 100 feet above sea level. Its streams drain into the Delaware River or Bay, and for much of their length they are tidal. The Coastal Plain is made up of sediments, mostly silt, sand, and gravel, that have been eroded off the Piedmont and adjacent Appalachian Mountains. In cross section these sediments form a southeastward thickening wedge that increases from 0 feet at the Fall Line to over 10,000 feet along Delaware’s coast. Offshore, on the continental shelf, the sediments become even thicker with reported thicknesses of 8 to 10 miles. In the 1970s and 1980s, exploratory drilling in this thick pile of sediments found no commercial deposits of gas or oil, although one noncommercial gas deposit was discovered. Underlying the sand, silt, and gravel of the Coastal Plain lie consolidated rocks that geologists refer to as the basement. While test drilling into the basement near the Fall Line, metamorphosed and deformed rocks similar to those of the Piedmont were extracted; therefore, the basement is probably a subsurface extension of the Piedmont.

The contact between the sediments of the Coastal Plain and the basement is called an unconformity. An unconformity represents an interval of time during which no sediments are preserved to record geological events. In the Coastal Plain, the oldest sedimentary rocks beneath Delaware’s coast are of Late Jurassic to Early Cretaceous age (140–150 million years), and the basement rocks they overlie are of Paleozoic age, older than 245 million years.

During the time represented by this unconformity, the rocks we see in the Piedmont today reached the earth’s surface as approximately 7 to 13 miles of overlying rock were removed by erosion allowing the buried rocks to rise to the surface in compensation. The oldest Coastal Plain sediments observed in Delaware are river-deposited sediments. These sediments were eroded from the Appalachian Mountains to the west, transported to the southeast by rivers, and deposited where the rivers met the ocean to form a delta. On top of the river sediments a sequence of marine silt and sand deposits records the rise and fall of the sea level many times during a period of over 80 million years, from the Late Cretaceous until the end of the Tertiary Period, about 2 million years ago.

On top of all of these sediments is a thin veneer of young sand and gravel that was carried into Delaware by glacial outwash during the Ice Age. Glacial ice did not advance into Delaware, but melt-water pouring off the glacier fronts carried great quantities of sand, silt, and gravel over southern Pennsylvania and Delaware. Delaware’s largest mineral resource is the sand and gravel deposited from the glacial outwash.

Most of the information and figures obtained from SP20 Delaware Piedmont Geology

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Delaware State Mineral - Sillimanite

Delaware State Mineral - Sillimanite johncallahan Sat, 06/27/2009 - 00:13
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Sillimanite, a white to tan to green aluminum silicate, (Al2SiO5) occurs in high temperature, aluminum-rich metamorphic rocks. In Delaware, it is found in the Hoopes Reservoir and Brandywine Springs areas.

In 1977, the Delaware General Assembly, acting on a proposal by the Delaware Mineralogical Society, established sillimanite as the Delaware State Mineral. This act recognizes the geological and mineralogical significance of the large masses of this mineral found as boulders at Brandywine Springs, an occurrence that was recognized as important in the 6th (1892) edition of Dana's System of Mineralogy. The Brandywine Springs boulders are remarkable for their size and purity. The sillimanite has a fibrous texture reminiscent of wood and could potentially be cut into cabochon gems showing a chatoyant ("cat's eye") effect. Sillimanite is not mined as an ore or raw material In Delaware.

Sillimanite forms at temperatures greater than 550oC, and its coarse grain size at Brandywine Springs indicates a prolonged period of high-temperature metamorphism of the rocks. These conditions are confirmed by the absence of muscovite and the occurrence of the pair sillimanite + K-feldspar (second sillimanite zone) in the schists/gneisses and by the presence of micropegmatites in the fold noses of the schists/gneisses, which are interpreted as partial melts of the rock under high-temperature conditions.

Delaware Facts and Symbols from Delaware.gov

Delaware State Fossil - The Belemnite

Delaware State Fossil - The Belemnite johncallahan Sat, 06/27/2009 - 00:12
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Belemnite is the common name applied to an extinct order (Belemnoida) of mollusks belonging to the cephalopod class. Modern cephalopods include the squid, octopus, and pearly Nautilus. The belemnoid animal was most closely related to the squid as it had an internal shell covered by a leathery skin, tentacles that pointed forward, and a siphon that expelled water forward thus moving the animal backward by jet propulsion. The internal shell of the belemnoid was cone-shaped and divided into chambers that were gas-filled for maintaining buoyancy in the sea. The chambered shell had a blade-like forward extension that is seldom preserved as a fossil. The most common fossilized part of the internal shell is called the "guard" or "cigar" consisting of a massive, generally brown-colored, subcylindrical structure called the rostrum that encloses the chambered shell and extends to the rear where it tapers to a conical apex. The rostrum served as a counter-weight to the buoyancy provided by the chambered shell and also for protection of that delicate shell. Belemnoids reached their greatest abundance and diversity during the Jurassic and Cretaceous periods.

On July 2, 1996, Belemnitella americana was named as the official fossil of Delaware. The Martin Luther King, Jr. Elementary School (Wilmington) third grade Quest students of Kathy Tidball suggested honoring the ancient and noble belemnite as our State fossil.(Delaware Code Title 29 § 314)

Belemnites have been found abundantly in the exposures of the Mount Laurel Formation along the banks of the Chesapeake and Delaware Canal in Delaware, east of St. Georges. The fine-grained sands and silts of the Mount Laurel were deposited in a shallow sea during the Late Cretaceous time around 70 million years ago. The fossil belemnite species found here is Belemnitella americana. Sometimes, almost complete belemnite guards can be found, similar in size and shape to a pencil, pointed at one end, but flaring at the other end (if preserved) and partly hollow in the center where the chambered shell was located. Often, only rod-like broken sections of the brown rostrum are found.

In Delaware, the best place to look for Belemnitella americana is in the dredge spoil piles on the north side of the Chesapeake and Delaware Canal, just west of St. Georges and also just east of the north side of the Reedy Point Bridge.

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Highest point in Delaware

Highest point in Delaware johncallahan Thu, 11/01/2012 - 21:56
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For many years, there has been a question in the minds of some Delawareans as to whether Delaware's highest elevation is Centreville or on Ebright Road.

The Delaware Geological Survey (DGS) at the University of Delaware, through its relationship to the National Geodetic Survey (NGS) has determined that the highest monumented spot in Delaware is located on Ebright Road, near the Pennsylvania state line. Ebright Road is north of Namaans Road, east of route 202.

The Ebright Road benchmark (NGS disk EBRIGHT AZI) was found to be 447.85 feet above sea level. Many people consider Centreville, Delaware to be the highest point in the state; however, a benchmark at Centreville has an elevation of only 445.58 feet making the Ebright Azimuth disk more than two feet higher.


Additional surveying by NGS and DGS personnel and 2007 LiDAR-derived contours indicate that areas just west of Ebright Road are at least two feet higher than the Ebright Azimuth benchmark elevation at around 450 feet. Therefore, according to DGS scientists, the highest actual elevation in Delaware is around 450 feet above sea level. These areas are shown in the map below. The areas within the 450 foot contour lines are highlighted in red.

It's a common misconception that Delaware's High Point at Ebright is the lowest of all US States' high points. This was based on a question in the popular trivia game Trivial Pursuit. In fact, Florida has the lowest high point at 345 feet (Britton Hill, on the Panhandle, near Lakewood.) Actually, Delaware would have the third lowest high point if Washington DC became a state (Fort Reno at 429ft).

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Piedmont Geology

Piedmont Geology johncallahan Thu, 06/24/2010 - 22:49

Overview of the Piedmont

Overview of the Piedmont johncallahan Sat, 06/27/2009 - 00:08
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The Appalachian Piedmont and Atlantic Coastal Plain are physiographic provinces that are separated by the fall zone. The fall zone (also called the Fall Line) is the contact where the hard crystalline rocks of the Piedmont dip under and disappear beneath the sediments of the Coastal Plain. The landscape and rock types shown in northern Delaware are classical examples of the larger geologic features that dominate the geology of eastern North America.

There are reasons why the major cities line up parallel to the coast and in accordance with the trend of the mountains. The fall zone was the limit of navigation to the European explorers. This and the availability of fresh water suggested the location of the initial settlements. Earth materials in the region—stone, sand and gravel, brick and china clay, mica, and feldspar—sustained economic development for several hundred years. Waterpower provided energy essential to the Industrial Revolution. Commerce and communication by ship benefited by access to tidewater. Northeast-southwest land travel and communication benefited from the relatively flat topography of the inner Coastal Plain. No wonder that our initial population concentrated along the fall zone. Delaware's Piedmont provides outstanding illustrations of the influence of geology on our history and society. Our forebears lived close to the land and understood its basic dictates. Pressures of land use and environmental protection now prompt us to rediscover the essentials of geology and apply modern science to advance applications appropriate to today’s needs.

Image of the Fall Line from the USGS National Atlas: http://nationalatlas.gov/articles/geology/features/fallline.html

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Geologic History of the Delaware Piedmont

Geologic History of the Delaware Piedmont johncallahan Mon, 09/21/2009 - 14:44
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The Delaware Piedmont is but a small part of the Appalachian Mountain system that extends from Georgia to Newfoundland. This mountain system is the result of tectonic activity that took place during the Paleozoic era, between 543 and 245 million years ago. Since that time, the mountains have been continuously eroding, and their deep roots slowly rising in compensation as the overlying rocks are removed. It is surprising to find that although the Delaware Piedmont has passed through the whole series of tectonic events that formed the Appalachians, the mineralogy and structures preserved in Delaware were formed by the early event that occurred between 470 and 440 million years ago, called the Taconic orogeny. This event was triggered by the formation of a subduction zone off the coast of the ancient North American continent that slid oceanic crust on the ancient North American plate beneath oceanic crust on the overriding plate, produced magma, and fueled an arc-shaped chain of volcanoes. This volcanic arc existed in the late Precambrian-early Paleozoic along most of the eastern margin of the ancient North American continent (Fig A). In Delaware, there is some evidence in the Wilmington Complex to suggest that the overriding oceanic plate included a small island cored by continental crust.

As convergence continued, most of the sediments deposited on the subducting plate were scraped off to form a thick pile of deformed and metamorphosed rocks. In Delaware this accreted pile of sediments became the Wissahickon Formation. The many amphibolite layers in the Wissahickon suggest that these sediments may have been mixed with ash falls, basalt flows from the volcanoes, or slivers of underlying oceanic crust that were broken off during scraping (Fig B). Eventually, continued convergence dragged the ancient North American continent into the subduction zone where it collided with the volcanic arc and pushed up a gigantic mountain range (Fig C). The creation of this range signified the end of the Taconic orogeny along the Appalachians. Today the once lofty mountains have eroded away leaving their roots exposed in the rolling hills of Delaware’s Piedmont. The intense metamorphism that occurred when the root zone was deeply buried in the base of the mountain range has obscured most of the rocks’ original features; however, careful study has recognized a series of rock units that represents the ancient continental margin.

The amphibolites and "blue rocks" of the Wilmington Complex were formerly a volcanic island that existed seaward of the ancient North American continent about 500 million years ago. The gneisses of the Wissahickon Formation represent sediments deposited in a deep ocean basin between the volcanic island and the continental shelf. The pure white crystalline marble of the Cockeysville Marble is the metamorphosed equivalent of a carbonate bank or reef that formed just off the ancient shoreline. The impure quartzites of the Setters Formation were certainly dirty beach sands, and the Baltimore Gneiss that forms the basement under the Setters and Cockeysville formations is billion-year-old rock, assumed to be a remnant of the ancient North American continent (Figs A, B, and C).

The rocks in the Delaware hills are still eroding (Fig D); their surfaces are fractured, broken, and covered with moss and lichen. As the rocks disintegrate, small pieces wash into the creeks and rivers to begin a journey that may take them to the Atlantic Ocean where they will be buried on the continental margin. Millions of years from now subduction may begin again off Delaware’s shore, and these sediments will be caught in another cycle of mountain building and erosion.

Common Rocks and Minerals of the Delaware Piedmont

Common Rocks and Minerals of the Delaware Piedmont johncallahan Thu, 06/24/2010 - 23:27
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The Red Clay Creek has flowed through the rolling hills of northern Delaware for many thousands of years, cutting a deep valley into the old deformed rocks of the Appalachian Piedmont. The Red Clay valley contains many of the common rocks found throughout the Delaware Piedmont.

Igneous Rocks

Igneous rocks are those that form by the crystallization of a hot molten liquid called magma or lava. We can see igneous rocks form today where lava erupts from volcanoes and cools to form solid rock. If it was not for volcanoes, it might be difficult to convince anyone that rocks can form from molten lava. Igneous rocks that form on the Earth’s surface are called volcanic rocks or extrusive igneous rocks.

Not all molten rock rises from deep within the Earth to erupt in a volcano. Sometimes the molten rock, or magma, does not reach the surface, but is held in big underground chambers where it slowly solidifies to form intrusive igneous rocks. We can see this type of igneous rock only where erosion has removed the overlying rocks.

Extrusive and intrusive igneous rocks can be distinguished by the size of their mineral grains. If the individual crystals are too small to be seen without magnification, the rock is fine-grained and probably extrusive. If you can easily differentiate the grains, it is considered coarse-grained and intrusive. Extrusive rocks are fine-grained because lava cools quickly and large grains do not have time to form. Intrusive rocks cool slowly deep inside the Earth and have time to grow large mineral grains.

The igneous rocks exposed in the Red Clay Valley are mostly coarse-grained, intrusive rocks that are named granites, granitic pegmatites, diorites, and gabbros. These rocks form in large masses usually without the layering that is characteristic of sedimentary and metamorphic rocks.

Common Igneous Rocks of the Red Clay Valley
Rock Type Description
Extrusive
Basalt A fine-grained, dark-colored, extrusive igneous rock that forms
by the crystallization of lava flows. Most basalt flows in the Red Clay Valley have been metamorphosed to amphibolites and are now composed of plagioclase, pyroxene, and amphibole.
Intrusive
Granite A coarse-grained, light-colored rock composed of quartz and two feldspars (plagioclase and orthoclase), with lesser amounts of mica or amphibole.
Gabbro A coarse-grained rock composed of greenish-white feldspar (mostly plagioclase) and pyroxene. Gabbro is usually very dark in color. It is the intrusive equivalent of basalt.
Pegmatite An igneous rock with very large (usually > one inch), well-formed crystals. A granitic pegmatite has the mineralogy of a granite and abnormally large grains, whereas a gabbroic pegmatite has the mineralogy of a gabbro and very large grains.
Diorite A coarse, uniformly grained rock composed of a feldspar and less than 50% amphibole or pyroxene. A quartz diorite has the composition of a diorite plus quartz and biotite, whereas a granodiorite has the composition of a diorite plus quartz and two feldspars.
 

Metamorphic Rocks

Metamorphic rocks are sedimentary or igneous rocks that have been changed. These changes usually occur deep within the Earth, by processes we cannot observe; however, we do know that under the lithosphere the mantle is a slowly churning reservoir of fiery hot rock. Thus, when rocks are deeply buried, they are heated from the reservoir below and squeezed from above by the overlying rocks. At these high temperatures and pressures, some minerals will become unstable and change into new minerals. For example, clay will change into mica, mica plus quartz will change into sillimanite, and chlorite will change into garnet. The mineral changes that occur in solid rocks as they are heated and deeply buried are known as metamorphism.

Common metamorphic rocks are slate, schist, gneiss, quartzite, marble, and amphibolite. The dominant rocks in the Delaware Piedmont are gneisses and amphibolites, rocks that were highly metamorphosed by heating deep within a subduction zone.

Common Metamorphic Rocks of the Red Clay Valley
Rock Type Description
Gneiss A course-grained rock commonly having imperfect, but prominent light-dark layering. In the Delaware Piedmont the light layers are composed of feldspars and quartz and the dark layers of mica, garnet, sillimanite, amphiboles, and pyroxenes.Gneisses are formed by the high-grade metamorphism of either igneous or sedimentary rocks.
Schist A sharply layered, commonly crinkle-folded rock, that can easily split into flakes or slabs due to a well developed parallelism of platy minerals such as micas or amphiboles. Schists commonly form by the medium-grade metamorphism of igneous and sedimentary rocks.
Amphibolite A rock composed primarily of amphibole and feldspar. The amphibole grains are commonly elongated with long axes parallel. In the Delaware Piedmont most amphibolites are formed by the metamorphism of igneous rocks.
Serpentinite A greenish-yellow, greasy soft rock composed essentially of the mineral serpentine. It may be soft enough to carve with a pocketknife. Serpentenites are formed by the metamorphism of ultramafic (iron-magnesium rich) rocks. Ultramafics originate deep in oceanic crust and occur on land only as slivers of rock that have been thrust faulted onto the continental margin.
Quartzite A massive rock composed essentially of interlocking quartz grains. Quartzites are formed by metamorphism of sand or sandstone.
Vein Quartz A rock composed of sutured quartz crystals that formed by precipitation from a solution or melt. In the Piedmont vein quartz commonly fills ancient fractures.
Marble A massive, coarse-grained sparkling blue-white rock composed mostly of calcite and/or dolomite. Marble forms by the metamorphism of limestone.
 

Sedimentary Rocks

Sedimentary rocks are made up of the debris from weathering and erosion of rocks, from chemical precipitates, or from the remains of living things. Most sedimentary rocks are formed from particles of older rocks that are carried by rivers and streams to lakes or oceans where they are deposited, deeply buried, and then consolidated into solid rock. They cover most of the ocean floor and three-quarters of the land. The most common solid sedimentary rocks are shale, sandstone, conglomerate, and limestone.

The only sedimentary rocks in Delaware’s Piedmont are modern sediments (sand, silt, and clay) that are being eroded, transported, and deposited in the local streams as the rocks within the watersheds weather and erode. The Piedmont has been a source of sediment that is deposited elsewhere, and has been for a long part of geologic time.

 

Minerals

At some time almost everyone has picked up and examined a rock. It may have been round and smooth and you liked the way it felt; it may have been just the right size to skip across a pond; or it may have been beautiful or unusual. Whatever your reason for picking up a rock, we hope you observed that it was made up of many small individual grains. These small grains are minerals. Most common everyday rocks, such as granite, slate, or gneiss, are made up of several different minerals, but it is possible for a rock, such as quartzite, to be composed of only one mineral. The dictionary broadly defines a mineral as a naturally occurring solid with a definite chemical composition and an ordered (crystalline) atomic arrangement.

Minerals can form in many ways, such as crystallization from a lava or magma, by recrystallization when a rock is heated or compressed, or by precipitation from water. Usually new minerals crystallize in a medium where they are competing for space with other minerals that are forming at the same time, and they end up as a maze of interlocking grains. However, if the minerals are allowed to crystallize without competition, such as in water or molten magma, the minerals will crystallize into geometric shapes that are strikingly beautiful and often valued by collectors. There are thousands of different minerals that form in the Earth, but only a few are found in the Red Clay Valley.

Common Minerals of the Red Clay Valley
Rock Type Description
Quartz A glassy, transparent to translucent mineral that breaks and fractures like glass. Its color is usually white to gray. Quartz is present in almost all Piedmont rocks.
Feldspar In weathered rocks or granitic pegmatites, feldspars occur as milky white or pink porcelain-like minerals that often break into rectangular shapes with shiny flat surfaces. In fresh, unweathered amphilbolites or gneisses, the feldspars are glassy and transparent. In the 18th and 19th centuries, feldspar was quarried in the Red Clay Valley for use in porcelain, china, and glazes. Orthoclase and plagioclase are two types of feldspar found in the Delaware Piedmont.
Mica A mineral with perfect basal cleavage that easily separates into sheets. The varieties are black biotite, white muscovite, bronze phlogopite, and green chlorite. Micas are common in all Piedmont rocks except the high-grade gneisses of the Wilmington Complex.
Garnet Most Piedmont garnets are a dark-red, iron-rich variety called almandine. They usually occur as 12-sided crystals that vary in size from crystals so small they can be seen only under a microscope to crystals of an inch or more across. Garnets are considered semi-precious stones, but in the highly deformed rocks of the Piedmont they are usually fractured and not suitable for jewelery. Garnet is also used as an abrasive.
Sillimanite Sillimanite, or fibrolite as it is commonly called, occurs as aggregates of thin fibers, nodules, or veins. Its color is either gray blue or dull white. It is a high-grade metamorphic mineral that occurs in the gneisses and granitic pegmatites. Sillimanite is the Delaware State Mineral.
Calcite and Dolomite The major minerals in marble. In the Delaware Piedmont they occur in the Cockeysville Marble as blue-white, coarsely crystalline interlocking grains. Years ago the marble was quarried, converted into quick lime, and used as a soil conditioner.
Serpentine A secondary mineral that forms by the alteration of magnesium-rich minerals. Serpentines are always shades of green, they are soft, and have a slightly soapy or greasy feel
Amphibole A large family of minerals. In the Delaware Piedmont, they are usually black or dark green. Amphiboles usually have one good cleavage that will sparkle on fresh surfaces. Arock containing around 50% or more amphibole is called an amphibolite.
Pryoxene A group of dark minerals that are common in the Piedmont rocks. They usually occur as interlocking grains in the highest-grade gneisses, amphibolites, and gabbros.

Deformation in the Piedmont

Deformation in the Piedmont rockman Tue, 06/30/2009 - 15:38
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All of the rock units in Delaware’s Piedmont are highly deformed. Deformational features, such as folds, faults, and/or joints, are present in almost every outcrop.

The folds are a remarkable assortment of sharp folds, angular crinkle folds, and round gentle folds that may be upright, inclined, or turned upside down. The variety can be attributed to several distinct episodes of folding, and to the different mechanical properties of the rocks. For example, the soft mica-rich gneisses of the Wissahickon were crinkle-folded, whereas during the same deformation the more rigid amphibolites were bent into rounded folds. Overall, the folds in the Piedmont suggest a long compressional event in soft rocks that were hot and deeply buried.

Although folding styles in the rocks vary dramatically, the trend of the folds is remarkably consistent across the Piedmont, and parallels the trend of the Appalachians as a whole, which is northeast-southwest. Folds permit determination of tectonic trends and are convenient indicators of crustal movements. Thus the folds in the Piedmont suggest a geologic setting at colliding plate boundaries, and the orientation of the folds indicates convergence from the southeast.

Today in the Delaware Piedmont there are no large active faults. Delaware is positioned on the trailing edge of the North American plate in a moderately active tectonic area. Several hundred million years ago, when Delaware was caught between two colliding plates, deep earthquakes were frequent and probably violent as regional faults stacked the various units in the Piedmont into a high mountain range. These ancient faults are difficult to identify, having been largely obscured by metamorphism and deformation.

Faults in cool brittle rocks may offset folds or layering across the fault surface, form a smooth slick surface called a slickenside, or grind up the rocks to produce fault gouge. These indicators of brittle faulting are present in the Piedmont rocks, but they are less common than folds and joints, and are younger features.

Almost all the rocks exposed in Delaware’s Piedmont are broken and fractured to form joints. If joints form in deeply buried rocks, they are normally healed with vein material, such as quartz or mixtures of quartz and feldspar. Because the Piedmont rocks were once deeply buried, healed veins are a prominent feature of these rocks. Most of these veins were healed before the major deformational events, and are now folded, stretched into thin layers, or pulled apart into segments.

Surface exposures of Wissahickon and Baltimore Gneiss rocks are riddled with very young horizontal and vertical joints, most likely the result of unloading and expansion as the overlying material is removed by erosion. Wilmington Complex rocks will joint and weather by peeling off a curved shell leaving round rocks. This jointing and weathering style is typical of massive, unlayered rocks. Thus, to a first approximation, it is possible to distinguish the rocks of the Wilmington Complex from those of the Wissahickon by the shape of the rocks at the surface. The Wissahickon rocks are angular and sharp whereas the Wilmington Complex rocks are round. The brittle fractures in the Piedmont rocks are important because they provide storage reservoirs for ground water. To produce water, the wells in northern Delaware must tap a fracture zone.

Piedmont Rock Units

Piedmont Rock Units johncallahan Tue, 06/30/2009 - 16:34
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The Piedmont occurs in the hilly northernmost part of the state and is composed of crystalline metamorphic and igneous rocks. These include a variety of rock types that were formed deep in the earth by metamorphic processes, mostly in the early part of the Paleozoic Era (app. 400-500 million years ago), and later uplifted. The rock units of the Wilmington Complex in the Piedmont are subdivided into geologic units called lithodemic units. These bodies of rock are identified by distinctive geological characteristics and are sufficiently thick and areally extensive to be mapped at the earth's surface and/or in the subsurface. Other rock units are mapped as formations. The age of the geologic units that are recognized in the Delaware Piedmont by the Delaware Geological Survey are summarized in the chart below. 

Abbreviations are those used on Delaware Geological Survey maps and cross sections. Geologic time scale not to scale.

For more details (breakdowns) of geologic time, please refer to:

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Piedmont Rock Unit Descriptions

Piedmont Rock Unit Descriptions johncallahan Thu, 06/24/2010 - 22:56

Ardentown Granitic Suite

Ardentown Granitic Suite johncallahan Mon, 07/27/2009 - 14:47

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Medium- to coarse-grained granitic rocks containing primary orthopyroxene and clinopyroxene; includes quartz norites, quartz monzonorites, opdalites, and charnockites. Feldspar phenocrysts common. Mafic enclaves locally abundant in proximity to gabbronorites.

Subtitle

Piedmont Unit

Formation Type
ardentown-granitic-suite
Geologic Unit Symbol
Sags
Geologic Time Period
Silurian

Baltimore Gneiss

Baltimore Gneiss johncallahan Tue, 07/28/2009 - 11:34

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Granitic gneiss with swirling leucosomes and irregular biotite-rich restite layers is the dominant lithology and constitutes approximately 75 to 80 percent of the exposed rocks. The remaining 20 to 25 percent comprises hornblende-biotite gneiss, amphibolite with or without pyroxene, and pegmatite. Granitic gneiss is composed of quartz, plagioclase, biotite, and microcline. Minor and accessory minerals are garnet, muscovite, magnetite, ilmenite, sphene, apatite, and zircon. The hornblende gneiss contains plagioclase, quartz, hornblende, and biotite with/without orthopyroxene. Accessory minerals are garnet, muscovite, clinozoisite, perthitic orthoclase, iron-titanium oxides, sphene, and apatite. Amphibolites are composed of subequal amounts of hornblende and plagioclase with minor quartz, biotite, clinopyroxene, and orthopyroxene.

Subtitle

Piedmont Unit

Geologic Unit Symbol
Pbgn
Geologic Time Period
Precambrian

Barley Mill Gneiss

Barley Mill Gneiss johncallahan Tue, 07/28/2009 - 10:01

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse-grained, foliated tonalite gneiss. Major minerals are biotite, hornblende, plagioclase, and quartz. Includes mafic enclaves or layers composed of subequal amounts of hornblende and plagioclase. Also includes a coarse-grained granitic lithology composed of biotite, microcline, plagioclase, and quartz.

Subtitle

Piedmont Unit

Formation Type
barley-mill-gneiss
Geologic Unit Symbol
Obmg
Geologic Time Period
Ordovician

Biotite Tonalite

Biotite Tonalite rockman Wed, 06/02/2010 - 13:05

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Fine- to medium-grained, equigranular biotite tonalite usually occurring as rounded boulders. Tonalites are leucocratic (15 to 25% modal mafic minerals), light gray to buff on fresh surfaces, and locally contain mafic enclaves with reddish rims, the result of iron hydroxide staining. Possibly intrusive into the Perkins Run Gabbronorite Suite.

Subtitle

Piedmont Unit

Formation Type
biotite-tonalite
Geologic Unit Symbol
Sbt
Geologic Time Period
Silurian

Brandywine Blue Gneiss

Brandywine Blue Gneiss johncallahan Mon, 07/27/2009 - 16:37

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Medium to coarse grained granulites and gneisses composed of plagioclase, quartz, orthopyroxene, clinopyroxene, brown-green hornblende, magnetite, and ilmenite. Mafic minerals vary from

Subtitle

Piedmont Unit

Formation Type
brandywine-blue-gneiss
Geologic Unit Symbol
Obbg
Geologic Time Period
Ordovician

Bringhurst Gabbro

Bringhurst Gabbro johncallahan Mon, 07/27/2009 - 14:44

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse- to very coarse-grained gabbronoite with subophitic textures. Primary minerals are plagioclase, olivine, clinopyroxene and orthopyroxene. Olivine, where present, is surrounded by an inner corona of orthopyroxene and an outer corona of pargasitic hornblende, both with spinel symplectites. The gabbronorites locally contain abundant xenoliths of mafic Brandywine Blue Gneiss. (GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005)

Subtitle

Piedmont Unit

Formation Type
bringhurst-gabbro
Geologic Unit Symbol
Sbg
Geologic Time Period
Silurian

Christianstead Gneiss

Christianstead Gneiss johncallahan Tue, 07/28/2009 - 10:08

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse-grained, foliated granodioritic gneiss. Major minerals are biotite, microcline, plagioclase, and quartz. Includes thin layers of fine-grained foliated amphibolite plus large pegmatites.

Subtitle

Piedmont Unit

Formation Type
christianstead-gneiss
Geologic Unit Symbol
Ochg
Geologic Time Period
Ordovician

Cockeysville Marble

Cockeysville Marble johncallahan Tue, 07/28/2009 - 11:18

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

In Delaware, predominantly a pure, coarsely crystalline, blue-white dolomite marble interlayered with calc-schist. Major minerals in the marble include calcite and dolomite with phlogopite, diopside, olivine, and graphite. Major minerals in the calc-schist are calcite with phlogopite, microcline, diopside, tremolite, quartz, plagioclase, scapolite, and clinozoisite. Pegmatites and pure kaolin deposits and quartz occur locally.

Subtitle

Piedmont Unit

Formation Type
cockeysville-marble
Geologic Unit Symbol
Ocm
Geologic Time Period
Cambrian to Ordovician

Faulkland Gneiss

Faulkland Gneiss johncallahan Tue, 07/28/2009 - 10:10

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Predominantly fine- to coarse-grained amphibolites and quartz amphibolites with minor felsic rocks, probably metavolcanic. Major minerals are amphibole and plagioclase with or without pyroxene and/or quartz. Amphibole may be hornblende, cummingtonite, gedrite, and/or anthophyllite. Halos of plagioclase and quartz around porphyroblasts of magnetite, orthopyroxene, and garnet are common features.

Subtitle

Piedmont Unit

Formation Type
faulkland-gneiss
Geologic Unit Symbol
Ofg
Geologic Time Period
Ordovician

Iron Hill Gabbro

Iron Hill Gabbro johncallahan Mon, 07/27/2009 - 14:41

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Black to very dark green, coarse- to very coarse-grained, uralitized olivine-hypersthene gabbronorite and pyroxenite with subophitic textures. Primary minerals are calcic plagioclase, orthopyroxene, clinopyroxene, and olivine. Amphibole is secondary, a pale blue-green actinolite. Olivine, when present, is surrounded by coronas similar to those in the Bringhurst Gabbro. The gabbronorite is deeply weathered leaving a layer of iron oxides, limonite, goethite, and hematite, mixed with ferruginous jasper. The jasper contains thin seams lined with drusy quartz. Contacts with the Christianstead Gneiss are covered with sediments of the Coastal Plain.

Subtitle

Piedmont Unit

Formation Type
iron-hill-gabbro
Geologic Unit Symbol
Sihg
Geologic Time Period
Silurian

Metapyroxenite and metagabbro (undifferentiated)

Metapyroxenite and metagabbro (undifferentiated) johncallahan Tue, 07/28/2009 - 10:57

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Light-colored coarse-grained rocks composed of interlocking grains of light colored, fibrous amphiboles, most likely magnesium-rich cummingtonite and/or anthophyllite with possible clinochlor. These rocks become finer grained and darker as hornblende replaces some of the Mg-rich amphiboles. Associated with the metapyroxenites are coarse-grained metamorphosed gabbros composed of hornblende and plagioclase. The metapyroxenites and metagabbros are probably cumulates.

Subtitle

Piedmont Unit

Formation Type
metapyroxenite-metagabbro
Geologic Unit Symbol
mpg
Geologic Time Period
Cambrian to Ordovician

Mill Creek Metagabbro

Mill Creek Metagabbro johncallahan Tue, 07/28/2009 - 09:56

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse-grained gabbroic and metagabbroic rocks, variably metamorphosed and deformed. Primary minerals are hornblende and plagioclase.

Subtitle

Piedmont Unit

Formation Type
mill-creek-metagabbro
Geologic Unit Symbol
Omcm
Geologic Time Period
Ordovician

Montchanin Metagabbro

Montchanin Metagabbro johncallahan Tue, 07/28/2009 - 09:58

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse-grained gabbroic and metagabbroic rocks, variably metamorphosed and deformed. Primary igneous minerals include olivine, clinopyroxene, orthopyroxene, and plagioclase.

Subtitle

Piedmont Unit

Formation Type
montchanin-metagabbro
Geologic Unit Symbol
Omm
Geologic Time Period
Ordovician

Pegmatite

Pegmatite johncallahan Tue, 07/28/2009 - 10:29

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Coarse- to very coarse-grained granitic pegmatite with tourmaline crystals locally. Where outcrop is present, pegmatite is tabular and concordant with the regional trend of the underlying Wissahickon Formation. Lenticular xenoliths of Wissahickon gneisses occur locally in the pegmatite.

Subtitle

Piedmont Unit

Formation Type
pegmatite
Geologic Unit Symbol
p
Geologic Time Period
lower Paleozoic

Perkins Run Gabbronorite Suite

Perkins Run Gabbronorite Suite johncallahan Mon, 07/27/2009 - 16:34

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Fine- to coarse-grained gabbronorite and minor diorite with subophitic to ophitic textures, variably foliated or lineated. Plagioclase, orthopyroxene, clinopyroxene, and hornblende are major minerals; biotite and olivine locally present. Olivine typically surrounded by corona structures as described for the Bringhurst Gabbro. Contemporaneous with the Ardentown Granitic Suite.

Subtitle

Piedmont Unit

Formation Type
perkins-run-gabbronorite-suite
Geologic Unit Symbol
Spgs
Geologic Time Period
Silurian

Rockford Park Gneiss

Rockford Park Gneiss johncallahan Tue, 07/28/2009 - 09:53

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Fine-grained mafic and fine- to medium-grained felsic gneisses interlayered on the decimeter scale. Layers are laterally continuous, but mafic layers commonly show boudinage. Felsic layers are composed of quartz and plagioclase with

Subtitle

Piedmont Unit

Formation Type
rockford-park-gneiss
Geologic Unit Symbol
Orpg
Geologic Time Period
Ordovician

Serpentinite

Serpentinite johncallahan Tue, 07/28/2009 - 11:03

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Massive fine-grained dark to light yellow-green serpentinite. Contacts with the Wissahickon Formation are not exposed.

Subtitle

Piedmont Unit

Formation Type
serpentinite
Geologic Unit Symbol
s
Geologic Time Period
Cambrian to Ordovician

Setters Formation

Setters Formation johncallahan Tue, 07/28/2009 - 11:28

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

In Delaware, predominantly an impure quartzite and garnet-sillimanite-biotite-microcline schist. Major minerals include microcline, quartz, and biotite with minor plagioclase, and garnet. Muscovite and sillimanite vary with metamorphic grade. Accessory minerals are iron-titanium oxides, zircon, sphene, and apatite. Microcline is an essential constituent of the quartzites and schists and serves to distinguish the Setters rocks from the plagioclase-rich schists and gneisses of the Wissahickon Formation.

Subtitle

Piedmont Unit

Formation Type
setters
Geologic Unit Symbol
Osq
Geologic Time Period
Cambrian to Ordovician

Windy Hills Gneiss

Windy Hills Gneiss johncallahan Tue, 07/28/2009 - 10:12

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Thinly interlayered, fine- to medium-grained hornblende-plagioclase amphibolite, biotite gneiss, and felsic gneiss, possibly metavolcanic. Felsic gneisses contain quartz and plagioclase with or without microcline with minor pyroxene and/or hornblende and/or biotite. Metamorphic grade in this unit decreases from granulite facies in the northeast to amphibolite facies toward the southwest. Correlated with the Big Elk Member of the James Run Formation in Cecil County, Maryland.

Subtitle

Piedmont Unit

Formation Type
windy-hill-gneiss
Geologic Unit Symbol
Owhg
Geologic Time Period
Ordovician

Wissahickon Formation

Wissahickon Formation johncallahan Tue, 07/28/2009 - 10:36

The following description is published in GM10 Bedrock Geologic Map of The Piedmont of Delaware and the Adjacent Pennsylvania, Schenck, W.S., Plank, M.O., and Srogi, L., 2000.

Interlayered psammitic and pelitic gneiss with amphibolite. Psammitic gneiss is a medium- to fine-grained biotite-plagioclase-quartz gneiss with or without small garnets. Contacts with pelitic gneiss are gradational. Pelitic gneiss is medium- to coarse-grained garnet-sillimanite-biotite-plagioclase-quartz gneiss. Unit has a streaked or flasered appearance owing to the segregation of garnet-sillimanite-biotite stringers that surround lenses of quartz and feldspar. Throughout, layers of fine to medium-grained amphibolite composed of plagioclase and hornblende, several inches to

Subtitle

Piedmont Unit

Formation Type
wissahickon
Geologic Unit Symbol
Owf
Geologic Time Period
Cambrian to Ordovician

Selected Outcrops of the Delaware Piedmont

Selected Outcrops of the Delaware Piedmont johncallahan Thu, 06/24/2010 - 23:06

Map of Selected Piedmont Outcrops

Map of Selected Piedmont Outcrops johncallahan Wed, 09/09/2009 - 17:22
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The Delaware Geological Survey maintains detailed records on outcrops located throughout the state. These records are completed by geologists when visiting the outcrop locations during field work. Many outcrops are on private property; however, we have selected several in the Piedmont area that are easily accessible and allow you to see some of the fascinating geology underlying northern Delaware. Each of the outcrops shown on this map has a small write up describing the mineralogical and structural details that can been seen in the rock outcrop. Please make sure to be respectful of property while observing these geologic treasures.

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Outcrop Ba14-a: The Setters Formation at Avondale Quarry

Outcrop Ba14-a: The Setters Formation at Avondale Quarry rockman Tue, 09/15/2009 - 13:52
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The Setters Formation is located in southeast Avondale, PA. Huge slabs of rock have been exposed by a gravel company that has been removing the hillside: quarrying for quartzite to sell as building stone and grinding pelitic rock into gravel and stone. These slabs have a foliation with a strike of 45 degrees East of North and a southeastern dip off of the Avondale Anticline. They also display quartzite, schist, and pods of pegmatite, containing large garnets (1-2" in diameter) and schorl tourmaline, that appear to be “sweated out of schist.” A dramatic contrast in rich type-shelf facies reflects beach sand and bogs or inlets. 

Latitude
39.82
Longitude
-75.78
Longitude2
-75.78
geolocation

39.82434, -75.776158

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Outcrop Bb25-c: The Yorklyn Railroad Cut

Outcrop Bb25-c: The Yorklyn Railroad Cut johncallahan Fri, 09/11/2009 - 10:43
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Wissahickon gneisses and amphibolites are exposed in the railroad cut near Yorklyn. Here the rocks are unusual because the layering is accentuated by the presence of fault gouge between the layers. Fault gouge forms as movement along a fault in hard, brittle rocks crushes and grinds the rocks into a powder. Gouge was a term used by miners because they could easily "gouge" it out of the rock. Here the gouge "weathered out" leaving deep indentations that emphasize the layering and the tilt, which is to the southeast at an angle of about 45 degrees. 

Elevation
180 ft.
Latitude
39.81
Longitude
-75.67
geolocation

39.807982, -75.67

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Outcrop Bc32-a: The Mt. Cuba Picnic Grove

Outcrop Bc32-a: The Mt. Cuba Picnic Grove johncallahan Fri, 09/11/2009 - 09:57
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The Mt. Cuba Picnic Grove provides an opportunity to look at the gneisses and amphibolites of the Wissahickon Formation. The large boulders of gneiss lying beside the steps are peppered with dark-red garnets and elongated nodules of dull-white sillimanite. These sillimanite nodules (1/4" to 3/4" long) are abundant in the gneisses at Mt. Cuba and are an interesting feature of these highly metamorphosed sedimentary rocks. Alternating layers of gneisses and amphibolites crop out on the east side of the track. The gneisses show some typical upright folds and fractures. Contacts between the layers trend northeast, parallel to the regional trend of the Appalachians.

Elevation
130 ft
Latitude
39.79
Longitude
-75.64
geolocation

39.789718, -75.64

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Outcrop Bc32-b: The Mt. Cuba Railroad Cut

Outcrop Bc32-b: The Mt. Cuba Railroad Cut johncallahan Fri, 09/11/2009 - 09:52
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The Mt. Cuba railroad cut is narrow and deep, and much of the rock is covered with dirt and soot from the train. The rocks are interlayered gneisses and amphibolites, with gneisses predominating in the south end of the cut and amphibolites in the north end. Folding is well developed, but the angle of the sunlight as it shines on the walls of the cut will determine which of the folds will be the easiest to see. A 4" amphibolite layer outlines the fold in this part of the outcrop. Wonderful examples of the effects of rock type on folding styles can be seen in the cut and in many of the rocks piled north of the cut.

Elevation
150 ft
Latitude
39.79
Longitude
-75.64
geolocation

39.792497, -75.64

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Outcrop Bc44-f: The Tatnall Preschool Grounds

Outcrop Bc44-f: The Tatnall Preschool Grounds rockman Thu, 12/10/2009 - 12:11
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The Tatnall Preschool Grounds contain many light-colored, coarse-grained, igneous-looking rocks (Barley Mill Gneiss) with mafic enclosures. These mafic enclosures make up only a small part of the rock. They may either be random in slope or they are elongated. When the Upper School and Preschool were built in the 1970s and 1980s, a lot of rock was removed from the foundations. The rock is either scattered around as large boulders in the landscaping, or in the back of the athletic fields in a large dump. The rocks in the dump show examples of mafic rock (greenish in color), part mafic and part pegmatite, and granitic rock. 

Latitude
39.77
Longitude
-75.61
geolocation

39.771024, -75.61

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Outcrop Bd21-a: Boulder Field at Brandywine Creek State Park

Outcrop Bd21-a: Boulder Field at Brandywine Creek State Park rockman Thu, 10/01/2009 - 12:18
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In the patch of woods north of the upper parking lot in Brandywine Creek State Park are large outcrops of amphibolite. The outcrops are rounded from exfoliation, and are black with few structural features. The mafic hornblende grains are elongated parallel to a few thin felsic bands. This lineation strikes east-west and dips to the north. These boulders are located on the northwest facing slope of the valley and are probably a paraglacial feature left over from a colder period in Delaware's geologic past. 

Latitude
39.81
Longitude
-75.58
geolocation

39.806667, -75.58

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Outcrop Bd41-b: Rockford Park Gneiss Boulders at Rockford Park

Outcrop Bd41-b: Rockford Park Gneiss Boulders at Rockford Park rockman Tue, 09/22/2009 - 15:20
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The Rockford Park boulders can be found just beyond the Rockford Tower on the slope facing the Brandywine Creek. Some areas of the Rockford Park Gneiss actually display some banding of felsic gneiss and mafic gneiss which are interlayered on a scale of 4" to 2'. This banding strikes 30 degrees east of north and dips 60 degrees to the northwest. The mafic layers are boudinaged and broken, some of which are weathered away into a prominent relief. Between some layers, the rock is intruded by a coarse-grained and apparently undeformed gabbro. 

Latitude
39.77
Longitude
-75.57
geolocation

39.768053, -75.57

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Outcrop Bd42-e: The Cliffs of Alapocas Woods

Outcrop Bd42-e: The Cliffs of Alapocas Woods rockman Tue, 09/22/2009 - 13:32
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Located in Wilmington, DE, the Cliffs of Alapocas Woods are opposite the old Bancroft Mills across the Brandywine Creek. Along the creek you will find large exposures of Brandywine Blue Gneiss. Compared to other outcrops in the Piedmont of Delaware, the rock examples here are massive. When observed closely, the felsic gneiss displays a medium grain size. Most of early Wilmington was built from the stone from these quarries. These impressive rock features are enjoyed by local rock climbers as well as many who use the Northern Delaware Greenway. 

Latitude
39.77
Longitude
-75.56
geolocation

39.769445, -75.56

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Outcrop Bd44-b: Bringhurst Gabbro boulders in Shellpot Creek

Outcrop Bd44-b: Bringhurst Gabbro boulders in Shellpot Creek rockman Tue, 09/22/2009 - 15:55
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Found in the creek bed and flood plain, the large boulders in Shellpot Creek are excellent examples of Bringhurst Gabbro. The gabbro is very coarse-grained with crystals up to 2" long; however, variations in the grain size exist over a scale of a few inches. While observing this rock closely, one can occasionally find grains of orthopyroxene (possibly bronzite) up to 4" long. Some of the boulders have grains of olivine surrounded by double coronas of orthopyroxene, spinel, and hornblende. 

Latitude
39.77
Longitude
-75.52
geolocation

39.772776, -75.52

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Outcrop Be22-e: Ardentown Railside Boulders

Outcrop Be22-e: Ardentown Railside Boulders rockman Wed, 10/07/2009 - 14:48
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Located in Ardentown are a few silicic boulders just on the northwestern side of the railroad bridge that crosses the South Branch of Naaman Creek. These boulders are part of the Ardentown Granitic Suite. Some have very large (several cm) feldspar phenocrysts. Some display contacts between granitic rock and quartz-rich rock, which is probably metasedimentary rock due to the granular nature of quartz. 

Latitude
39.81
Longitude
-75.48
geolocation

39.808468, -75.48

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Outcrop Be21-e: Hanby Park Quarry

Outcrop Be21-e: Hanby Park Quarry rockman Thu, 10/01/2009 - 15:09
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On the south side of Chestnut Hill is an outcrop of very large boulders in the woods of Hanby Park near Arden, DE. This area of the park seems to be the site of an old quarry. The rocks here are very similar to the rocks found down the South Branch of Naaman Creek (Ardentown and Ardencroft) as they both share the same fine-grained, mafic properties with traces of coarse-grained charnockite. 

Latitude
39.81
Longitude
-75.49
geolocation

39.814997, -75.49

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Outcrop Be22-k: Charnockite Boulders at Ardentown

Outcrop Be22-k: Charnockite Boulders at Ardentown rockman Thu, 10/01/2009 - 11:59
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In the valley of the South Branch of Naaman Creek, through Ardentown, is a group of charnockite boulders and fine-grained mafic rock (probably amphibolitized gabbroid). The mafic rock is mostly non-megacrystic with some coarse-grained and equigranular charnockite. On the ground around the boulders are small pieces that contain a clear example of a contact between coarse-grained and fine-grained rock types. 

Latitude
39.81
Longitude
-75.48
geolocation

39.812492, -75.48

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Outcrop Be23-g: Charnockite Boulders in the South Branch of Naaman Creek

Outcrop Be23-g: Charnockite Boulders in the South Branch of Naaman Creek rockman Thu, 10/01/2009 - 13:16
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Running through Knollwood Park in Claymont, DE is the South Branch of Naaman Creek. This stream is laden with fairly mafic, medium to coarse-grained charnockite. Some of the charnockite samples here may be mylonitic. A few boulders contain xenoliths as well. Other gabbro boulders display charnockite veins in a gradational zone over about 1-2 meters. 

Latitude
39.81
Longitude
-75.45
geolocation

39.809815, -75.45

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Outcrop Be32-g: Lesher Park Streambed

Outcrop Be32-g: Lesher Park Streambed rockman Wed, 10/07/2009 - 15:08
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In Claymont, DE, the intersection of Marvel Avenue and Parkside Boulevard occurs at Lesher Park, which contains Perkins Run, a creek West of Harvey Road. In the streambed of this creek is an outcrop of Perkins Run Gabbro, which is part of the Arden Plutonic Supersuite. The gabbro displays joints that are oriented 10 degrees west of north. Along these joints, veins of charnockite (orthopyroxene-bearing granite of the Ardentown Granitic Suite) can be found. 

Latitude
39.80
Longitude
-75.48
geolocation

39.79527, -75.48

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Outcrop Ca44-d2: The Christianstead Subdivision

Outcrop Ca44-d2: The Christianstead Subdivision rockman Thu, 10/15/2009 - 14:33
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Outcrops between Hidden Valley Drive and Farmhouse Road. The Christianstead subdivision is underlain by interlayered mafic and felsic gneiss with large pegmatites. The felsic gneiss, in the northwestern half of this subdivision, is deformed granodiorite, seen as massive igneous layers with only rare crinkle folding. There are a few bright eyes textures on the west end of this subdivision, which is all underlain by granodiorite.

Latitude
39.70
Longitude
-75.78
geolocation

39.695001, -75.78

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Outcrop Cb15-c: The Confluence Quarry at North Pointe

Outcrop Cb15-c: The Confluence Quarry at North Pointe rockman Thu, 10/22/2009 - 13:54
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Just northwest of the confluence of Mill Creek and an unnamed tributary is an abandoned quarry. This quarry sits off the greenway trail, across from a ruined foundation wall, and displays samples of black, coarse-grained, foliated amphibolite. The unnamed tributary and Mill Creek are choked with amphibolite rocks and boulders. The amphibolite here weathers with a rusty rind and has a foliation strike of 10 degrees east of north and an obviously steep to vertical dip. 

Latitude
39.75
Longitude
-75.68
geolocation

39.746389, -75.68

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Outcrop Cb42-c: Windy Hills Bridge Outcrop

Outcrop Cb42-c: Windy Hills Bridge Outcrop rockman Thu, 10/22/2009 - 14:16
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Considered one of Delaware's most famous Piedmont outcrops, the Windy Hills Bridge outcrop is composed of mafic and felsic gneiss of the Windy Hills Gneiss. Much of the layering in the outcrop is regular and is 8 to 10" thick. At the contact between these layers there is evidence of partial melting. In terms of mineralogy, this rock contains mainly hornblende, plagioclase, quartz, biotite and epidote. This outcrop shows tight folds that plunge steeply 70-90 degrees to the northeast and southwest. The gneiss is cut by a long lens of pegmatite, which intruded after the folding and metamorphosing that yielded the gneiss. There is also an interesting layer of cobble just above the bedrock in this area presumed to be the contact with the Coastal Plain sediments. These newer outcrops to the southwest display a 4-10" pelitic layer which becomes more extremely magmatic, with 1" leucosomes and ½" mafic selvages. Overall, strikes of foliations of the mafic and felsic layering in these outcrops are 70-75 degrees east of north and the dips are a steep 80-85 degrees to the southeast, or almost vertical. 

Latitude
39.69
Longitude
-75.72
geolocation

39.69222, -75.72

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Outcrop Cc12-a: The Cave at Brandywine Springs

Outcrop Cc12-a: The Cave at Brandywine Springs johncallahan Wed, 09/09/2009 - 16:17
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Approximately 100 yards east of the tracks is one of the largest outcrops in the park. Here along the hillside, a thick layer of crinkle-folded, yellow-weathering gneiss overlies a layer of garnet-bearing quartzite and amphibolite. At the contact between the quartzite and the schist, a large piece of the quartzite has fallen out creating a small cave. Maybe Indians used this cave, but it is not very inviting. If you hit the black rocks with a hammer they will ring. Look for the tiny lavender garnets in the quartzite. 

Latitude
39.75
Longitude
-75.64
Longitude2
-75.64
geolocation

39.745832, -75.638328

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Outcrop Cc12-c: The Red Clay Creek Edge

Outcrop Cc12-c: The Red Clay Creek Edge rockman Tue, 11/17/2009 - 15:16
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Along the edge of the Red Clay Creek exists a large outcrop that extends out into the stream. This rock is part of the Wissahickon Formation, with pelitic facies, ½" elongated sillimanite nodules, and disharmonic folds. The compositional layering of this rock is 1/8“ ½" of biotite rich layers alternated with fine-grained psammitic layers (not quartz-feldspar layers). Some of these layers are sheared (shear zones). The sillimanite nodules, pegmatite pods, and shear zones in this rock are all parallel to fold axes. The axial plane of these folds is 20 degrees east of north, plunges 42 degrees northeast, and dips 90 degrees. Within this large outcrop are several 2-3' layers of “rock that rings” (when hit) and are folded with petitic gneiss. This pelitic gneiss shows more intense folding while the rest of the rock is gently folded. The “rock that rings” is also peppered with small lavender garnets.

Latitude
39.75
Longitude
-75.64
geolocation

39.745276, -75.64

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Outcrop Da15-h: The Paraglacial Boulder Feature of Chestnut Hill

Outcrop Da15-h: The Paraglacial Boulder Feature of Chestnut Hill rockman Tue, 09/22/2009 - 11:55
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Prime examples of Iron Hill Gabbro can be found in the area surrounding Chestnut Hill at Rittenhouse Park. The gabbro here is considered coarse to very coarse grained. Boulders of Iron Hill Gabbro are located on the northeast facing slope southwest of the Christina Creek. This gabbro boulder field is probably a paraglacial feature left over from ice age times deep in Delaware's geologic past. 

Latitude
39.65
Longitude
-75.76
geolocation

39.654168, -75.76

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Piedmont Field Trips - GeoAdventures

Piedmont Field Trips - GeoAdventures johncallahan Thu, 06/24/2010 - 23:11

What are GeoAdventures?

What are GeoAdventures? johncallahan Sat, 06/27/2009 - 00:15
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GeoAdventures are designed to allow the reader to learn about a particular geologic point of interest in Delaware’s Piedmont province and then take a short field trip to that area. Want to know more about the Wilmington blue rock or Brandywine blue granite? Take the Wilmington Blue Rock GeoAdventure and go see just what the blue rock looks like.

GeoAdventures are great for a family education outing, Boy or Girl Scout training, mineral or rock-collecting club, or Earth science school trips. See the whole Piedmont by reading Special Publication 20 and riding the Wilmington and Western Railroad steam train all along the Red Clay valley following the field trip guide in the back of the book.

Check these pages as new GeoAdventures will be continually added.

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Exploring the Wilmington Blue Rocks: A GeoAdventure in the Delaware Piedmont

Exploring the Wilmington Blue Rocks: A GeoAdventure in the Delaware Piedmont johncallahan Tue, 07/14/2009 - 12:03
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The Wilmington blue rock, Delaware's most famous rock, underlies both the city of Wilmington and the rolling upland north and east of the city. It is best exposed along the banks of the Brandywine Creek from south of Rockland to the Market Street Bridge. Along this section the Brandywine has carved a deep gorge in the blue rock. The water fall along this four mile gorge is approximately 120', and in the 17th and 18th centuries provided water power for one of the greatest industrial developments in the American colonies. The field trip stops described below are chosen as good examples of blue rock along the Brandywine Creek, and to illustrate how the geology has influenced the development of this area. It is not necessary to visit every stop to become familiar with the blue rocks, you may choose to visit only a few.

The specific objectives of this adventure are to:

  • Examine the igneous and metamorphic rocks of the Delaware Piedmont that have been called the Wilmington blue rock by quarrymen and the Brandywine Blue Gneiss of the Wilmington Complex by geologists.
  • Investigate the role played by the blue rocks in the ancient geologic history of northern Delaware which involves subduction of tectonic plates, formation of volcanoes, and the progressive collision of the North American, European, and African plates to form a huge mountain range. All of this tectonic activity occurred sometime between 570,000,000 and 250,000,000 years ago. Since that time northern Delaware has remained tectonically quiet as the mountains have slowly eroded their debris of clay, sand, and gravel, onto the continental shelf of the Atlantic Ocean.
  • Recognize how the bedrock and accompanying land forms have influenced land use and industrial development. At its peak in the 18th century, the Brandywine Creek flowing across the blue rocks provided energy for some 130 flour mills, paper mills, and textile mills. Later in the 19th century, in the gorge above Wilmington, the duPonts began the manufacture of gun powder, and from their beginning along the Brandywine, they have grown to be one of the giants of American industry.

GEOLOGIC SETTING

The rocks you will see on this trip are locally called the Wilmington blue rocks or Brandywine Blue Granite. When found in stream beds, yards, or old quarries, the rocks are black or dark gray, however when freshly broken during quarrying the rocks are a bright royal blue. Although weathering changes the color, construction workers have always called this rock the "blue rock". Recognizing the importance of these rocks to the city, Wilmington's original baseball team called themselves the blue rocks, a name that has since been adopted by the city's new baseball team.

Geologists map the blue rock by its geologic name "the Brandywine Blue Gneiss" and assign the rocks to a geologic unit called the Wilmington Complex. The Wilmington Complex forms the bedrock under the much of the city of Wilmington and Brandywine Hundred (Figure 1). The rocks are mostly a mixture of metamorphic gneisses and plutonic igneous rocks. The gneisses, which are the most abundant rock type, are the true "blue rocks". However when you see them today along the Brandywine, they are massive, solid, blue-gray rocks with few visible features to indicate their long history. Since their formation approximately 570,000,000 years ago, these rocks have experienced a long history of burial, high-grade metamorphism, deformation, uplift, and erosion. The metamorphism has totally recrystallized the rock to produce a monotonous body of rock that is wonderfully suited for building houses and fences. It is useless as road ballast as it breaks rock crushers so today the large boulders dug up during construction are usually buried off site.

The mineralogy of the blue rocks is simple, the rocks usually contain only four minerals; quartz, feldspar, pyroxene, and magnetite. Geologists have described this rock as a banded gneiss, even though the light-dark banding is weak and not always present. There are large areas that consist of only light gneiss or dark gneiss. The gneisses weather to form a white rind. It is only then that streaks of minerals up to one inch long can be seen on the white weathered surface. The dark streaks are usually pyroxene or magnetite and the lighter streaks are quartz and feldspar. The banding and the mineral streaks are the only features that are commonly seen in the blue rocks.

The tectonic setting proposed for the origin of the Wilmington Complex is thought to be the deep part of a volcano that developed over an east dipping subduction zone. The subduction and volcanism were early in a series of tectonic events that produced the Appalachian Mountain System. Later, probably between 480,000,000 and 440,000,000 million years ago, the volcanoes collided with the ancient North American continent. Because of this collision, the rocks of the ancient continent, the rocks in the volcanic range, and the rocks lying in the ocean between the continent and the range, were all folded, sheared and buried to depths of 10 to 12 miles where they were metamorphosed by extreme heat and pressure. For many years these buried rocks remained at very high temperatures, somewhere between the temperatures required for high-grade metamorphism and melting (around 1,300°F). Today, after uplift and erosion, the highly metamorphosed rocks are exposed in Delaware in what is recognized by geologists as the metamorphic core of the Appalachian Mountain System.

Coarse-grained igneous rocks are exposed in Bringhurst Woods Park and in the communities of Arden and the Timbers. These rocks probably intruded into the blue rocks and may be younger. They are undeformed and only slightly metamorphosed, thus it is good site to study intrusive igneous rocks (Bringhurst Gabbro GeoAdventure).

Use Figure 1 as a guide to where the 5 stops on this adventure are located.

Stop 1. Brandywine Creek State Park

Park in the lot on the east side of the Brandywine Creek just south of Thompson's Bridge Road. At this stop we will see the contact between the blue rocks of the Wilmington Complex and the metamorphic sedimentary rocks of the Wissahickon Formation. The contact runs northeast at 45 degrees parallel to the regional trend of the Appalachian Mountains, and is exposed along Rocky Run.

There are two options for this stop. Walk (1) follows the southeast side of Rocky Run and will take approximately one and one half hours. Some of the walk includes bushwacking off existing trails so this trip is not suitable for young children. The exposures on Walk (1) are abundant and are good examples of both the Wissahickon and Wilmington Complex rocks. Walk (2) follows the dirt road from the parking lot to the south and will take about one half hour. This is an easy walk and you will be able to see both the metasediments of the Wissahickon and the black boulders of the Wilmington Complex.

Walk (1)

  • Walk south along the Brandywine creek. The hillsides on the east of both the parking lot and the road expose large outcrops of the metamorphosed sediments of the Wissahickon Formation. Many of the outcrops are covered with fungus, making it necessary to look carefully to see the features of these rocks (Area marked A in Figure 2). Cross the bridge over Rocky Run. Take one of the paths that lead northeast parallel to Rocky Run (Figure 2B). A few Wilmington Complex boulders are strewn along the hillside, however approximately one quarter of a mile to the northeast you will encounter a large swale that is literally choked with hundreds of rounded boulders of Wilmington Complex blue rocks (Figure 2C). The boulders are dark, rounded, and show light-dark layering. If you look carefully you may see a few "bright eyes". The bright eyes are grains of black magnetite surrounded by white grains of feldspar and quartz. If you use your imagination, you can see the rocks are looking at you!. Geologists believe this field of boulders is to be a paraglacial feature, formed by freeze and thaw action. The boulders slowly worked their way downslope during the last glacial period, about 10-40 thousand years ago.
  • Cross the boulder field, turn left, and walk toward Rocky Run. Look for a wall of rock bordering the northwest side of Rocky Run (Figure 2D). Wissahickon rocks form the wall and the streambed while the rounded boulders of Wilmington Complex gneisses clog the stream, litter the southeast banks and lie scattered in the flood plain. The layering in the Wissahickon wall rock is irregular and defined by stringers of garnet, biotite and sillimanite in a mass of quartz and feldspar. The garnets are dark red, either oval or round, and may be as large as three quarters of an inch in diameter. The stringers, and any folds that are present, are best seen by standing in the stream and looking upstream. The contact between the Wissahickon and Wilmington rocks is hidden beneath the flood plain.
  • To see the contact, you need to follow the stream to the confluence of Hurricane Run and Rocky Run and stay on the northeast side of Rocky Run. (Figure 2E). The exposed contact is difficult to recognize and probably interesting only to geology students at the high school or college level. It is exposed in a ten foot area along the northeast side of Rocky Run where dark, fine grained Wilmington Complex gneisses are interlayered with light colored Wissahickon gneisses. The Wissahickon rocks appear to have been melted and recrystallized to form granites with thin layers of garnets. The biotite and sillimanite that occur in the Wissahickon gneisses are replaced by tiny garnets. This reaction in which garnet replaces biotite and sillimanite occurs only at very high temperatures. The Wilmington Complex layers vary in thickness between 3 inches and 2 feet, and are dark solid, massive rocks.
  • The nature of this contact is controversial. Geologists are unable to find any substantial evidence in the rocks that will allow them to determine how these two units were placed next to one another. The possibilities are: (1) the original volcanic pile that became the Wilmington Complex rocks was thrust up and over the Wissahickon sediments during subduction of the tectonic plates, (2) the Wilmington Complex slid down from the northeast, maybe from as far northeast as New York City, on a large regional strike slip fault such as the San Andres in California, or (3) that the contact is intrusive and the Wilmington Complex igneous rocks intruded the Wissahickon sediments before the metamorphism.
  • Return to the parking lot.

Walk (2)

  • Walk south along the Brandywine creek. The hillsides on the east of both the parking lot and the road expose large outcrops of Wissahickon rocks. Many of the outcrops are covered with fungus, making it necessary to look carefully to see the individual minerals and the layering (Area marked A in Figure 3). Look for large garnets and curving stringers of biotite and sillimanite.
  • Walk down the road and cross the bridge over Rocky Run. The contact between the Wissahickon and the Wilmington Complex occurs approximately 450 feet south of the bridge. At the contact the rocks in the roadbed change from the light colored, mica-rich rocks of the Wissahickon to dark, rounded boulders of the Wilmington Complex. These Wilmington Complex boulders dot the hillside east of the road. Most boulders are banded and some will contain "bright eyes" The "bright eyes" are grains of magnetite surrounded by light colored quartz and feldspar. If you use your imagination, you will see the rocks winking at you!
  • Return to parking lot.

Stop 2. Rockford Park

This is the most easily accessible stop and will take between fifteen minutes and a half an hour to observe the blue rocks at this location. Follow the main road in Rockford Park to the parking lot at the tower. Park and walk toward the Brandywine Creek. Along the ridge are large outcrops of sharply banded Wilmington Complex gneisses (location of "star" in Figure 4). The banding runs 40 degrees east of north, parallel to the regional strike of the Appalachian Mountain System. The layers are vertical, orientated perpendicular to the land surface.

The bands are 9 to 12 inches thick. During intense metamorphism, around 440,000,000 years ago, these rocks were totally recrystallized and stretched. During stretching, the dark bands were more rigid than the light bands and separated. The light bands were plastic and flowed between the separations. French geologists named this texture boudinage. It is caused by intense squeezing or stretching of the rock while it is warm and plastic.

The light bands are composed of quartz and plagioclase feldspar, with minor amounts (Stop 3. Quarries on Brandywine Creek, Alapocas

This quarry has recently been given to the county as part of its park system and can be accessed on the Delaware Greenway (location of "star" in Figure 5). Good exposures of Wilmington Complex gneiss or blue rock are found on the exposed back wall of the quarry. The rock is a monotonous, light-colored gneiss with a few thin dark bands. The dark bands appear to have been deformed by stretching or pulling apart and often occur as pieces about a foot long . Thicker dark bands may persist for the extent of the exposure. The dark bands probably represent original lava flows. This rock looks as if it has been squeezed and stretched. The stretching occurred many years ago when the rocks were hot and plastic. Today these rocks in the quarry are hard and brittle. They will no longer bend or fold, but they will fracture and break during earth movements such as earthquakes or erosional unloading.

Stop 4. Brandywine Park

Large boulders line the banks of the Brandywine as it flows through Brandywine Park. The boulders along the creek are blue rocks, but the banding is replaced by irregular layering and, in some rocks, the mafic bands are replaced by clots or pods of mafic rock (location A, B, C in Figure 6).

This stretch of the Brandywine was the location of many of the mills, thus the bedrock is much disturbed. A large mill race still exists on the southwest side of the creek, however in the 18th century mill races bordered both sides of the stream. The races carried water to turn water wheels and provide energy for the many mills built below the great falls near the Market Street Bridge. Below the Market Street Bridge the Brandywine is navigable, allowing ships to sail up the Christina and lower Brandywine to pick up the flour, cotton, and snuff from the mills that lined the stream.

The rock removed from the mill races was used to build homes for the mill owners and workers. Many of the houses and churches in Brandywine Village that have been built from blue rocks are now beautifully restored.

Stop 5. Swedes Landing

Old Swedes Landing, Fort Christina Park

This stop will take about one half an hour and is an easy interesting walk through the park at Old Swedes Landing to "The Rocks" in the Christina River (Figure 7).

In 1638 the Kalmar Nyckel and the Fogel Grip sailed up the Christina River past the entrance to the Brandywine to "The Rocks" where a large flat slab of blue rock protrudes into the main channel of the river. This rock slab was a convenient place to unload the weary passengers that were aboard the ships. The passengers, mostly Swedes and Finns, stayed and settled on the Christina near this site.

The large flat slab of rock on which the early settlers landed, although reduced to make room for river travel on the Christina, is still a present in Swedes Landing Park. "The Rock" is a slab of Wilmington Complex gneiss or blue rock, and marks the eastern edge of exposure of the Appalachian mountain system where the hard rocks of the Piedmont Province plunge beneath the soft sediments of the Coastal Plain. The boundary between the Piedmont and the Coastal Plain is defined in most places by a well-marked change in topography, usually an abrupt transition from rolling hills to a flat smooth lowland. Geologically it defines the transition from the hard crystalline rocks of the Piedmont to the gently dipping beds of younger clays, sands, and gravels of the Coastal Plain. This boundary is called the Fall Line, and extends along I-95 from Newark, through south Wilmington, toward the Delaware River. It is but a portion of the line or zone that extends unbroken from New York to Georgia. Many of the great cities of the east such as new York, Trenton, Philadelphia, Wilmington, Baltimore, Washington, Richmond Raleigh, and Macon are built on the Fall Line.

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Woodlawn Quarry: A GeoAdventure in the Delaware Piedmont

Woodlawn Quarry: A GeoAdventure in the Delaware Piedmont johncallahan Tue, 07/14/2009 - 11:04
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INTRODUCTION

A visit to Woodlawn Quarry is suitable for ages 10 to adults and provides an interesting opportunity to observe common mineral specimens, identify the quarry as an early mining site, appreciate the physical work necessary to quarry rock with hand tools, and discuss the economic importance of the minerals found in the quarry. The minerals that can be readily found and identified in the quarry are feldspar, quartz and mica.

This area was bought in 1910 by William Bancroft as a wild flower preserve. It is now part of the First State National Monument, a Federal National Monument within the National Parks System.

Feldspar was actively quarried at this site from 1850 to 1910. There were many feldspar quarries or spar pits as they were commonly called scattered throughout the Delaware Piedmont in the early eighteen hundreds. The feldspar recovered from this spar pit was transported by horse and wagon to a factory in Philadelphia where it was used for making porcelain products such as dishes, figurines, false teeth, or sinks. The quarry eventually closed because machinery made other sites more accessible.

GEOLOGIC SETTING

The rock quarried is an intrusive igneous rock called a granite. Intrusive rocks do not flow or explode from a volcano onto the earth's surface, but solidify deep within the earth. Molten rock called magma flows slowly through cracks or other zones of weakness in the local rock and cooled slowly to solidify into a rock made up of large mineral grains. The intrusive rock quarried here at Woodlawn names a graphic granite because the feldspar grains contain inclusions of quartz in geometric shapes that look like the cuneiform writing of the ancient Arabs. The graphic granite also contains white mica (Muscovite) and the accessory minerals garnet and beryl.

The graphic granite cooled and crystallized slowly within preexisting rock, called the country rock. The so-called country rock surrounding the graphic granite is part of the Wissahickon Formation, a formation made up of highly metamorphosed and intensely deformed rocks that formed in the core of the ancient Appalachian Mountains. The magma from which the granite crystallized probably formed during the metamorphism. This is a common occurrence in metamorphic terrains where the coarse grained granites are called pegmatites.

MINERAL IDENTIFICATION

The minerals found in this quarry can be distinguished by their physical properties, color, cleavage or fracture, and luster. Cleavage is the tendency of some minerals to break along definite surfaces that are parallel to possible crystal faces, and provides a means of identifying these minerals. Minerals without cleavage will break by fracturing or breaking in all directions. Not all minerals show good cleavage, most show fracture.

FELDSPAR occurs as two varieties, one is pink and one is white. All the feldspar grains a re opaque, that is light does not shine through the mineral. The feldspars break with good cleavage in two directions. The pink feldspar has better cleavage than the white and often breaks into small perfect rhombohedrons. The fresh cleavage surfaces have a pearly luster. The pink feldspar is a variety called microcline, and the white feldspar is plagioclase. Both feldspars form similar crystals, but have different elements in their crystal lattices. Plagioclase grains display surface striations due to exsolution during cooling.

QUARTZ grains are transparent to translucent, that means that light will pass through the grains. They occur here as crystalline masses that fracture like glass. The masses show a transition from clear white quartz to smoky quartz.

Quartz is the most common mineral in surface rocks. It is the principal constituent in many igneous sedimentary and metamorphic rocks and forms the sand on most of our beaches. It has many uses such as a gemstone, as an electronic component, as the principal component of glass.

MICA is easily recognized because it has perfect one directional cleavage and separates into thin elastic sheets. A cluster of sheets if referred to as a book and appears block and opaque. The sheets are clean and transparent, but may contain hexagonal-shaped inclusions (reticulated inclusions) of a black iron mineral. Separating the books into thin sheets illustrated the prominent basal cleavage. This colorless variety of mica is called Muscovite.

The sheets obtained from large books were use to make heat proof windows for old stoves and ranges. Because of their electrical resistance, the iron-free micas are widely used in many kinds of electrical equipment. The isinglass, popular years ago as shatterproof windows in automobiles was made using a sheet of mica and clear glass.

GARNET occurs here as tiny dark red crystals with 12 sides, called a dodecahedron. The crystals are rare and small and it is necessary to look carefully to find crystals. The garnets are hard, have a glassy luster and no distinct cleavage. When broken they look like dark red glass.

BERYL or aquamarine as it is commonly called, is pale blue-green. It has no cleavage and occurs here as irregular masses in the graphic granite. Beryllium is a rare element, and most granitic pegmatites do not contain beryl, however this occurrence is part of a group of beryl-bearing granitic rocks that have been identified in southern Chester and Delaware counties in Pennsylvania and northern New Castle county in Delaware. Both garnet and aquamarine are semiprecious stones.



This map shows the location of Woodlawn Quarry. As previously stated, it is now part of the First State National Monument, a Federal National Monument within the National Parks System and no mineral collecting is allowed.

The Bringhurst Gabbro: A GeoAdventure in the Delaware Piedmont

The Bringhurst Gabbro: A GeoAdventure in the Delaware Piedmont johncallahan Tue, 07/14/2009 - 11:51
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A field trip to Bringhurst Woods Park is appropriate for students in grades 5 and up (10 years and older), and provides an opportunity to observe intrusive plutonic igneous rocks that have intruded into country rock, which in this case is the blue rock or what geologists call the Brandywine Blue Gneiss. In addition, the minerals in the pluton are large, easily identified, and interesting. Mineral collecting is not allowed within the park, however permission may be obtained to collect along Shellpot Creek southeast of the park. Please do not use rock hammers on the rocks in the park.



The specific objectives of this adventure are:

  • To observe an intrusive igneous rock and the country rock (Wilmington blue rock) it has intruded
  • To identify the individual minerals in an igneous rock

Geologic Setting

The rocks along Shellpot Creek in Bringhurst Woods Park are intrusive igneous or plutonic rocks. Because of the good exposure in this park, geologists have named these rocks the Bringhurst Gabbro and mapped the pluton as a geologic unit within the Wilmington Complex (Figure 1). The Bringhurst Gabbro represents a magma flow that flowed into the Wilmington Complex and cooled deep underground. The rocks of the Wilmington Complex underlie the most City of Wilmington and Brandywine Hundred. During the 18th and 19th centuries all rock units within the Wilmington Complex were extensively quarried for building houses, fences, retaining walls, schools, churches, and factories. They were used wherever a building material was needed. The most common rock unit in the Wilmington Complex is a high-grade metamorphic rock called the Brandywine Blue Gneiss (commonly called the Wilmington blue rock). This "blue rock" was named for the bright blue color of the rock when it is freshly exposed. It is the Wilmington blue rock that the Bringhurst Gabbro intruded.

The Bringhurst Gabbro exposed along Shellpot Creek has not been deformed or recrystallized by metamorphism, thus the rocks of the Bringhurst pluton lack the layering found in most of the other metamorphic rocks of the Delaware Piedmont. Because there are no fine-grained "chilled margins" at the contact between the pluton and the Wilmington blue rock, the pluton probably intruded the gneisses while they were still hot, sometime in the early Paleozoic between 500,000,000 and 400,000,000 million years ago.

THE ROCKS

Shellpot Creek in Bringhurst Woods Park is choked with large rounded boulders of Bringhurst Gabbro that have eroded out of the surrounding hills. A close look shows the minerals in the gabbro are between 1/4 and 2 inches in length and 1/4 to 1 inch in diameter (Figure 2). Blobs of fine-grained dark rock are common in the Bringhurst pluton. These dark blobs are chunks of Wilmington blue rock that were picked up and incorporated into the magma as it intruded into the gneiss. These inclusions are called xenoliths, a word derived from the root xeno- meaning foreign and lithos- meaning rock. Thus, a xenolith is a foreign rock enclosed within another rock. In this case the xenoliths are derived from the country rock, the Wilmington blue rock. Although the Wilmington blue rock is composed of both dark layers and light layers, all the xenoliths are derived from the dark layers. This is possibly because the light-colored inclusions melted at a lower temperature than the dark inclusions, and the light inclusions melted in the hot gabbroic magma of the pluton becoming commingled and no-longer recognizable.

A contact between the coarse grained rocks of the pluton and the Brandywine Gneiss occurs approximately 700 to 800 ft east of the park entrance (Figure 1). The gneiss at the contact is contorted and contains clots of quartz.

Before a field trip to Bringhurst Wood Park, it is recommended the group visit one of the Wilmington Complex stops described in the Wilmington Blue Rocks Geologic Adventure, so the participants can recognize the Wilmington blue rock.

MINERAL IDENTIFICATION

Minerals of the Bringhurst pluton (Figure 2) are plagioclase feldspar, pyroxene and olivine. The plagioclase is dark gray and glassy. Feldspar has two distinct cleavages, thus when a feldspar crystal is broken along a cleavage plane it will present a smooth shiny surface. The pyroxene crystals are elongated, black or bronze colored, and may have a distinctive schiller or iridescent luster on a fresh surface. The olivine grains are less common than the pyroxene, and in this pluton, the olivine grains are usually rusty and have a black rim. Individual minerals in the rims cannot be recognized in hand specimens, but microscopic study has identified an inner rim that is an intergrowth of orthopyroxene with spinel and an outer rim that is an intergrowth of hornblende with spinel. The olivine-bearing rocks are more abundant southwest of the park entrance.

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Coastal Plain Geology

Coastal Plain Geology johncallahan Thu, 06/24/2010 - 23:36

Geologic History of the Delaware Coastal Plain

Geologic History of the Delaware Coastal Plain johncallahan Sat, 06/27/2009 - 00:21
Body

Delaware lies within two physiographic provinces, the Appalachian Piedmont and the Atlantic Coastal Plain. The Fall Zone divides these two provinces. The major events in the evolution of the Piedmont rocks occurred between 500 and 200 million years ago.

A great period of time, of which there is no record in Delaware, passed before the deposition of the oldest sediments of the Coastal Plain, the Potomac Formation, during the latter part of Early Cretaceous time, about 120 million years ago. Streams transported clays with interbedded sands from the Appalachian mountains which lay to the northwest and deposited them in rivers and swamps. This process continued into the Late Cretaceous resulting in a wedge of sediments with a thickness of about 4,000 feet in southern Delaware. During the Late Cretaceous, between 100 million and 65 million years ago, sea level rose, and marine sediments were deposited across Delaware. The sands of the Potomac Formation form the Potomac aquifer which provides water to residents of New Castle County.

A small unconformity, or period of nondeposition, separates the Potomac Formation from the overlying Magothy Formation. The white sands and lignitic black silts of the Magothy form a distinctive marker indicating the transition from the older sediments to the later marine deposits.

During the Cenozoic, between 65 million years ago and the present, sea level rose and fell multiple times depositing coastal and marine sediments across a large area of the Delaware Coastal Plain. In Delaware, these deposits are called the Rancocas and Chesapeake Groups. These large stratigraphic groups are subdivided into many formations. The sands in these formations form aquifers which provide water for southern Delaware.

The most recent phase of deposition occurred about 2.4 million years ago when glaciers advanced and retreated across the northern part of North America during the early Pleistocene period. The Beaverdam Formation, which is found over much of southern Delaware, is the result of climate change which transported much of the weathered soils and rocks of the Appalachian Piedmont toward the ocean. The Columbia Formation, which is found in the northern part of the Delaware Coastal Plain, consists primarily of sand with gravel generated by the first glaciers that advanced into the Delaware and Susquehanna River basins. The Beaverdam and Columbia Formations comprise the surficial Columbia aquifer, which provides much of the water for irrigation and domestic wells throughout Kent and Sussex counties.

During the middle to late Pleistocene, sea level rose during warm periods and receded during glacial periods. When sea level was high, (higher than present sea level), sediments were deposited along the margins of the Atlantic Ocean and the Delaware River in environments much like those found along the coast today. During the times when the glaciers were at their maximum in central Pennsylvania,northern New Jersey, and Delaware experienced very cold and windy climates which resulted in the formation of permafrost features and sand dunes across much of its area. Sea level has been rising over the last 12,000 years, advancing the shoreline landward.

Total thickness of all coastal plain units is about 8,000 feet (at Fenwick Island).

Coastal Plain Rock Units (Stratigraphic Chart)

Coastal Plain Rock Units (Stratigraphic Chart) johncallahan Wed, 07/01/2009 - 00:59
Body

The geology of Delaware includes parts of two geologic provinces: the Appalachian Piedmont Province and the Atlantic Coastal Plain Province. The Piedmont occurs in the hilly northernmost part of the state and is composed of crystalline metamorphic and igneous rocks. These include a variety of rock types that were formed deep in the earth by metamorphic processes, mostly in the early part of the Paleozoic Era (app. 400-500 million years ago), and later uplifted. The Coastal Plain, a flatter area that comprises most of the state, is underlain by a series of younger layers of sediments, ranging in age from the Cretaceous Period (app. 120 million years ago) to relatively recent. These have been slightly tilted through geologic time, with very minor faulting or folding in places.

The rocks and sediment layers of both of Delaware's geologic provinces can be subdivided into geologic units called lithodemic units (for the crystalline rocks) or lithostratigraphic units (for the sedimentary units). These bodies of rock are identified by distinctive geological characteristics and are sufficiently thick and areally extensive to be mapped at the earth's surface and/or in the subsurface. The chart below summarizes the age and distribution of the geologic units that are recognized in the state by the Delaware Geological Survey.

Rock Unit Stratigraphic Chart of the Coastal Plain

Abbreviations are those used on Delaware Geological Survey maps and cross sections. Geologic time scale not to scale.

For more details (breakdowns) of geologic time, please refer to:

Coastal Plain Rock Unit Descriptions

Coastal Plain Rock Unit Descriptions johncallahan Thu, 06/24/2010 - 23:44

Assawoman Bay Group

Assawoman Bay Group siteadmin Fri, 08/20/2010 - 11:45

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Assawoman Bay Group consists of the well-sorted sands, silts, and clays of the Omar, Ironshire, and Sinepuxent Formations found adjacent to and inland of the Atlantic Coast of Delaware and Maryland. These deposits in Delaware and Maryland were named from oldest to youngest: the Omar Formation (Jordan, 1962, 1964), the Ironshire Formation (Owens and Denny, 1979), and the Sinepuxent Formation (Owens and Denny, 1979).

The Assawoman Bay Group consists of transgressive deposits that were deposited along the margins of an ancestral Atlantic Ocean during middle to late Pleistocene highstands of sea level. It is named for the Little Assawoman Bay in Delaware and the Assawoman Bay in Maryland in the vicinity of where the Omar, Ironshire, and Sinepuxent Formations are best developed. In Delaware, the Assawoman Bay Group extends south of Indian River Bay to east of Gumboro. In Maryland, it is mapped south and west of Salisbury (Owens and Denny, 1979). It extends east of Salisbury into the Virginia portion of the Delmarva Peninsula (Mixon, 1985).

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qabg
Geologic Time Period
middle to late Pleistocene
Reference(s)

Jordan, R.R., 1962, Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological Survey Bulletin No. 9, 51 p.

_____, 1964, Columbia (Pleistocene) sediments of Delaware: Delaware Geological Survey Bulletin No. 12, 69 p.

Mixon, R.B., Berquist, C.R., Jr., Newell, W.L., Johnson, G.H., et al., 1989, Geologic map and generalized cross sections of the Coastal Plain and adjacent parts of the Piedmont, Virginia: U.S. Geological Survey Miscellaneous Investigations Series Map I-2033, scale 1:250,000.

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Beaverdam Formation

Beaverdam Formation johncallahan Mon, 07/27/2009 - 13:45

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Heterogeneous unit ranging from very coarse sand with pebbles to silty clay. Predominant lithologies at land surface are white to mottled light-gray and reddish-brown, silty to clayey, fine to coarse sand. Laminae and beds of very coarse sand with pebbles to gravel are common. Laminae and beds of bluish-gray to light-gray silty clay are also common. In a few places near land surface, but more commonly in the subsurface, beds ranging from 2- to 20-ft thick of finely laminated, very fine sand and silty clay are present. The sands of the Beaverdam Formation commonly have a white silt matrix that gives drill cuttings a milky appearance (Ramsey, 2001, 2007). This white silt matrix is the most distinguishing characteristic of the unit and readily differentiates the Beaverdam Formation from the adjacent clean sands of the Turtle Branch Formation. Interpreted to be a fluvial to estuarine deposit of late Pliocene age on the basis of pollen assemblages and regional stratigraphic relationships (Andres and Ramsey, 1995a, 1996; Groot and Jordan, 1999; Groot et al., 1990). Ranges from 50 to 120 ft thick in the Georgetown Quadrangle.



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light gray to white coarse to very coarse sand with beds of fine to medium sand. Sands are quartzose, moderately feldspathic (

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Beaverdam
Geologic Unit Symbol
Tbd
Geologic Time Period
upper Pliocene
Reference(s)

Andres, A.S., and Ramsey, K.W., 1995a, <a href="/publications/gm9-geology-seaford-area-delaware">Geology of the Seaford area, Delaware: Delaware Geological Survey Geologic Map No. 9</a>, scale 1:24,000.

_____, 1995b, <a href="/publications/ofr39-basic-data-geologic-map-seaford-area-delaware">Basic data for the geologic map of the Seaford area, Delaware: Delaware Geological Survey Open File Report 39</a>, 39 p.

_____, 1996, <a href="/publications/ri53-geology-seaford-area-delaware">Geology of the Seaford area, Delaware: Delaware Geological Survey Report of Investigations No. 53</a>, 22 p.

Groot, J.J., Ramsey, K.W., and Wehmiller, J.F., 1990, <a href="/publications/ri47-ages-bethany-beaverdam-and-omar-formations-southern-delaware">Ages of the Bethany, Beaverdam, and Omar formations of southern Delaware: Delaware Geological Survey Report of Investigations No. 47</a>, 41 p.

Groot, J.J., and Jordan, R.R., 1999, <a href="/publications/ri58-pliocene-and-quaternary-deposits-delaware-palynology-ages-and-paleoenvironments">The Pliocene and Quaternary deposits of Delaware: palynology, ages, and paleoenvironments: Delaware Geological Survey Report of Investigations No. 58</a>, 19 p.

Ramsey, K. W., 2001, <a href="/publications/gm11-geology-ellendale-and-milton-quadrangles-delaware">Geologic map of the Ellendale and Milton quadrangles, Delaware: Delaware Geological Survey Geologic Map Series No. 11</a>, scale 1:24,000.

_____, 2007, <a href="/publications/gm14-geologic-map-kent-county-delaware">Geologic Map of Kent County, Delaware: Delaware Geological Survey Geologic Map Series No. 14</a>, scale 1:100,000.

Bethany Formation

Bethany Formation siteadmin Mon, 08/16/2010 - 11:03

The following description was published in RI67 The Cat Hill Formation and Bethany Formation of Delaware, Andres, A.S., 2004:

The composition, thickness, and geophysical log signature of the Bethany Formation vary with location and depth. In general, the Bethany Formation is a sequence of clayey and silty beds with discontinuous lenses of sand (Andres, 1986; Ramsey, 2003). The most common lithologies are silty, clayey fine sand; sandy, silty clay; clayey, sandy silt; fine to medium sand; sandy, clayey silt, and medium to coarse sand with granule and pebble layers. Thin gravel layers occur most frequently in updip areas and are rarer in downdip areas. Sands are typically quartzose. Lignite, plant remains, and mica are common, grains of glauconite are rare. In the Lewes area, Ramsey (2003) describes the Bethany Formation as consisting of gray, olive gray, bluish-gray clay to clayey silt interbedded with fine to very coarse sand. Lignitic and gravelly beds are common.

Variations in thickness reflect spatial changes in depositional environments during filling of the sedimentary basin and post-depositional erosional truncation (Andres, 1986). The age of the Bethany Formation is reported to range from late middle Miocene (Owens and Denny, 1979; Hansen, 1981; Benson, 1990) to perhaps Pliocene (Miller et al., 2003), although the age estimates are poorly constrained because of a general lack of diagnostic fossils or other materials that can be age-dated.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
bethany
Geologic Unit Symbol
Tbt
Geologic Time Period
late Miocene to Pliocene
Reference(s)

Andres, A.S., 1986, <a href="/publications/ri42-stratigraphy-and-depositional-history-post-choptank-chesapeake-group">Stratigraphy and depositional history of the post-Choptank Chesapeake Group: Delaware Geological Survey Report of Investigations No. 42</a>, 39 p.

Benson, R. N., ed., 1990, with contributions by A. S. Andres, R. N. Benson, K. W. Ramsey, and J. H. Talley, <a href="/publications/ri48-geologic-and-hydrologic-studies-oligocene-pleistocene-section-near-lewes-delaware">Geologic and hydrologic studies of Oligocene-Pleistocene section near Lewes, Delaware: Delaware Geological Survey Report of Investigations No. 48</a>, 34 p.

Hansen, H. J., 1981, Stratigraphic discussion in support of a major unconformity separating the Columbia Group from the underlying upper Miocene aquifer complex in eastern Maryland: Southeastern Geology, v. 22, p. 123-138.

Miller, K. G., McLaughlin, P. P., Jr., Browning, J. V., Benson, R. N., Sugarman, P. J., Ramsey, K. W., Hernandez, J., Baxter, S. J., Feigenson, M. D., Monteverde, D. H., Cramer, B. S., Uptegrove, J., Katz, M. E., McKenna, T. E., Strohmeier, S. A., Pekar, S. F., Cobbs, G., Cobbs, G., III, Aubry, M.-P., and Curtin, S., 2003, Bethany Beach site report, in Miller, K.G., Sugarman, P. J., Browning, J.V., et al., Proc. ODP, Init. Repts., 174AX (Suppl.), 1-84 [Online]. Available at: http://www.odp.tamu.edu/publications/174AXSIR/VOLUME/CHAPTERS/174AXS_3….

Owens, J. P. and Denny, C. S., 1979, Upper Cenozoic deposits of the central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Ramsey, K. W., 2003, <a href="/publications/gm12-geology-lewes-and-cape-henlopen-quadrangles-delaware">Geologic Map of the Lewes and Cape Henlopen quadrangles, Delaware: Delaware Geological Survey Geologic Map Series No. 12</a>, scale 1:24,000.

Bridgeton Formation

Bridgeton Formation johncallahan Tue, 07/28/2009 - 12:07

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to brown, medium to very coarse, poorly sorted sand to silty quartz sand containing scattered gravel beds. Less than 15 ft thick and underlies a relict terrace flat that has elevations between 170 ft and 180 ft and parallels the present Delaware River. More extensive to the north in Pennsylvania (Owens, 1999; Berg et al., 1980).

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Bridgetown
Geologic Unit Symbol
Tbr
Geologic Time Period
Miocene
Reference(s)

Berg, T.M., Edmunds, W.E., Geyer, A.R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, scale 1:250,000, 3 sheets.

Owens, J.P., 1999, Cretaceous and Tertialy, <em>in</em> Shultz, C.H., editor, The Geology of Pennsylvania: Pennsylvania Geological Survey Special Publication No. 1, p. 219-223.

Bryn Mawr Formation

Bryn Mawr Formation johncallahan Tue, 07/28/2009 - 12:10

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to yellowish-brown silty quartz sand to sandy silt that interfingers with medium to coarse clayey sand with gravel. Sand fraction, where a sandy silt, is fine- to very fine-grained and angular to subangular. Iron-cemented zones are common. Gravel fraction is primarily quartz. Sands are quartzose with minor amounts of weathered feldspar. Opaque heavy minerals form up to 3 percent of the sand fraction. Unit ranges up to 70 ft thick but generally less than 30 ft thick and commonly less than 10 ft thick. Surface forms a distinctive terrace that has elevations between 350 ft and 425 ft, and it overlies saprolite of the Piedmont rocks. No macrofossils have been recovered. Fossil pollen from the York Pit in Cecil County, Maryland (Pazzaglia, 1993; unpublished DGS data) indicate a Miocene age. Owens (1999) considered the unit late Oligocene in Pennsylvania.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Bryn-mawr
Geologic Unit Symbol
Tbm
Geologic Time Period
Miocene
Reference(s)

Owens, J.P., 1999, Cretaceous and Tertiary, <em>in</em> Shultz, C.H., editor, The Geology of Pennsylvania: Pennsylvania Geological Survey Special Publication No. 1, p. 219-223.

Pazzaglia, F.J., 1993, Stratigraphy, petrography, and correlation of late Cenozoic middle Atlantic Coastal Plain deposits: implications for late-state passive-margin geologic evolution: Geological Society of America Bulletin, v. 105, p. 1617-1634.

Calvert Formation

Calvert Formation johncallahan Mon, 07/27/2009 - 13:58

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Gray to grayish-brown, clayey silt to silty clay interbedded with gray to light-gray silty to fine to coarse quartz sands. Discontinuous beds of shell are common in the sands and in the clayey silts. Found in the subsurface throughout Kent County. Interpreted to be a marine deposit. Rarely the surficial unit on the uplands in northwestern Kent County where the Columbia or Beaverdam Formations are absent. Outcrops are patchy and are too small to be shown on this map. Three major aquifers are found within the Calvert Formation in Kent County: the Frederica, Federalsburg, and Cheswold, from top to bottom, respectively (McLaughlin and Velez, 2006). Ranges up to 425 feet thick.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Gray to grayish-brown clayey silt to silty clay interbedded with gray to light-gray silty to fine to coarse quartz sands. Discontinuous beds of shell are common in the sands and in the clayey silts. The unit ranges up to 100 ft in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
calvert
Geologic Unit Symbol
Tc
Geologic Time Period
lower to middle Miocene
Reference(s)

McLaughlin, P.P., and Velez, C.C., 2006, <a href="/publications/ri72-geology-and-extent-confined-aquifers-kent-county-delaware">Geology and extent of the confined aquifers of Kent County, Delaware: Delaware Geological Survey Report of Investigations No. 72</a>, 40 p.

Cat Hill Formation

Cat Hill Formation johncallahan Thu, 05/06/2010 - 18:05

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Yellowish-brown to light-gray, medium to fine sand with thin beds and laminae of medium to coarse sand and scattered pebbles (B) that grades downward into bioturbated, gray, very fine sand to silt (A). Rare beds of light-gray to red silty clay are found near the contact with the overlying Beaverdam Formation. Laminae of opaque heavy minerals are present in the upper sands. Laminae of very fine organic particles are found in the lower sand as well as laminae to thin beds of coarse sand to gravel. The burrows in the lower sand are clay lined, and in some intervals, the sediment is completely bioturbated to the extent that no sedimentary structures are preserved. Sand is primarily quartz with less than 5% feldspar and a trace to less than 1% mica (in the very fine sand to silt). Glauconite is present only in trace amounts. Fragments of lignite are common to rare in the organic laminae. Interpreted to be a late Miocene, very shallow marine to marginal marine (shoreface) deposit (McLaughlin et al., 2008). About 100 to 120 ft thick in the Georgetown Quadrangle.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Cat-hill
Geologic Unit Symbol
Tcat
Geologic Time Period
Late Miocene

Choptank Formation

Choptank Formation johncallahan Mon, 07/27/2009 - 13:54

Description published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light gray to blue gray, fine to medium, shelly, silty, quartz sand and clayey silt. Discontinuous beds of fine sand and medium to coarse quartz sand are common. Base of the unit is marked by a coarse to granule sand that fines upwards to a medium to fine silty sand. This sand is the Milford aquifer (Ramsey, 1997; McLaughlin and Velez, 2006). In southern Kent County, can be subdivided into upper and lower unit. Lower unit consists of the fining-upward sequence from the basal sand to a hard clayey silt to silty clay that ranges in color from grayish brown to bluish gray. Upper unit consists of clean to silty, fine to medium, moderately shelly sands with thin silty clay beds. Rarely found in outcrop in the upper reaches of some of the more deeply incised streams. Outcrops are too small to be shown on this map. Found in the southern half of Kent County. Up to 140 feet thick in the southernmost part of the county.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
choptank
Geologic Unit Symbol
Tch
Geologic Time Period
middle to upper Miocene
Reference(s)

McLaughlin, P.P., and Velez, C.C., 2006, <a href="/publications/ri72-geology-and-extent-confined-aquifers-kent-county-delaware">Geology and extent of the confined aquifers of Kent County, Delaware: Delaware Geological Survey Report of Investigations No. 72</a>, 40 p.

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion Quadrangles, Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Columbia Formation

Columbia Formation johncallahan Mon, 07/27/2009 - 13:43

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three feet in thickness. Scattered beds of tan to reddish-gray clayey silt are common. In places, the upper 5 to 25 feet consists of grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near the base, clasts of cobble to small boulder size have been found in a gravel bed ranging from a few inches to three feet thick. Gravel fraction primarily quartz with lesser amounts of chert. Clasts of sandstone, siltstone and shale from the Valley and Ridge, and pegmatite, micaceous schist, and amphibolite from the Piedmont are also present. Fills a topographically irregular surface, is less than 50 feet thick, and is interpreted to be primarily a body of fluvial glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during the middle Pleistocene (Groot and Jordan, 1999). Ramsey (2010) considered the Columbia to be lower Pleistocene.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Yellowish- to reddish-brown, fine to coarse, feldspathic quartz sand with varying amounts of gravel. Typically cross-bedded with cross-sets ranging from a few inches to over three ft in thickness. Scattered beds of tan to reddish-gray clayey silt common. In places, the upper 5 to 25 ft a grayish- to reddish-brown silt to very fine sand overlying medium to coarse sand. Near base of unit, clasts of cobble to small boulder size found in gravel bed ranging from a few inches to three ft thick. Gravel fraction consists primarily of quartz with lesser amounts of chert. Clasts of sandstone, siltstone, and shale from the Valley and Ridge Province, and pegmatite, micaceous schist, and amphibolite from the Piedmont are present. The Columbia fills an eroded surface and ranges from less than 10 ft thick to over 100 ft. Primarily a body of glacial outwash sediment (Jordan, 1964; Ramsey, 1997). Pollen indicate deposition in a cold climate during middle Pleistocene (Groot and Jordan, 1999).

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Columbia
Geologic Unit Symbol
Qcl
Geologic Time Period
lower Pleistocene
Reference(s)

Groot, J.J., and Jordan, R.R., 1999, <a href="/publications/ri58-pliocene-and-quaternary-deposits-delaware-palynology-ages-and-paleoenvironments">The Pliocene and Quaternary deposits of Delaware: palynology, ages, and paleoenvironments: Delaware Geological Survey Report of Investigations No. 58</a>, 19 p.

Jordan, R.R., 1964, <a href="/publications/b12-columbia-pleistocene-sediments-delaware">The Columbia sediments of Delaware: Delaware Geological Survey Bulletin No. 12</a>, 69 p.

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Ramsey, K.W., 2010, Stratigraphy, correlation, and depositional environments of the middle to late Pleistocene interglacial deposits of southern Delaware: Delaware Geological Survey Report of Investigations No. 76, 43 p.

Cypress Swamp Formation

Cypress Swamp Formation siteadmin Mon, 08/16/2010 - 10:31

The following description was published in RI62 The Cypress Swamp Formation, Delaware, Andres, A.S. and Howard, C.S., 2000:

The upper part of the Cypress Swamp Formation is a multi-colored, thinly bedded to laminated, quartzose fine sand to silty fine sand, with areally discontinuous laminae to thin beds of fine to coarse sand, sandy silt, clayey silt, organic silt, and peat. The lowermost 3 to 6 ft of the unit are commonly composed of thin beds of dark-colored, organic-rich, clayey silt with laminae to thin beds of fine sand and peat. Fine sand to fine sandy silt are present at the base of the unit in boreholes where the lower organic-rich beds are absent. Dark-colored, peaty, organic-rich silt and clayey silt with laminae of fine to medium sand as much as 4.5 ft thick are common within 5 ft of land surface, but may be absent in some locations. Colors are shades of brown, gray, and green where the unit contains visible organic matter, and orange, yellow, and red at shallow depths where the organic-rich beds are absent. Clay-sized minerals are a mixed suite that includes kaolinite, chlorite, illite, and vermiculite.

Subtitle

Coastal Plain - Primarily Surface Unit

Formation Type
Cypress-swamp
Geologic Unit Symbol
Qcs
Geologic Time Period
late Pleistocene to Holocene

Deal Formation

Deal Formation siteadmin Mon, 08/16/2010 - 11:52

The following description was published in Bulletin 20 Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware, Benson, R.N., and Spoljaric, N., 1996:

It is a clayey, calcareous, shelly, glauconitic (10-20 percent) silt. Its colors range from greenish-gray and gray-green to brownish-gray and light gray. It is rich in calcareous and siliceous microfossils. The matrix mineralogy shows a high calcite component, except in the lower part of the formation which is within a calcite dissolution interval. In the lower half of the formation quartz is predominant.

Aragonite is rare or several levels except for the uppermost part of the formation where it shows a significant peak as the Deal grades upward into the Piney Point Formation. Marcasite and, to a lesser extent, pyrite also show major peaks at the same level. Feldspar, dolomite, pyrite, siderite, hematite, analcine, jarosite, alunite, goethite, vivianitc, and phillipsite are present in trace amounts at various levels.

A significant feature of the opaque heavy mineral assemblage is the increase in the amount of andalusite, which replaces tourmaline as the dominant heavy mineral in much of the Upper (middle Eocene) part of the Deal. Kyanite, zircon, rutile and garnet are subordinate constituents, and silliminite increases in the uppermost Deal. Clay minerals are glauconite/smectite, kaolinite, chlorite/smectite, and illite/smectite.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
deal
Geologic Unit Symbol
Td
Geologic Time Period
Paleocene to middle Eocene

Delaware Bay Group

Delaware Bay Group johncallahan Tue, 07/28/2009 - 11:55

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Delaware Bay Group consists of transgressive deposits that were laid down along the margins of ancestral Delaware Bay estuaries during middle to late Pleistocene rises and highstands of sea level. The Delaware Bay Group was described in detail by Ramsey (1997).

The Delaware Bay Group deposits consist of light reddish-brown to gray, medium to medium-to-coarse sands with common beds of fine to medium sand and very fine to fine sand and very fine to fine sandy silt. Also present are beds of gray clayey silt and brown, organic-rich clayey silt that are commonly found in lensoid channel-fill bodies. Beds of gray, fine to very fine clayey sand to clayey silt with shell are found in its eastern extent near Rehoboth Beach. The sands are quartzose with varying amounts of feldspar, slightly less than quantities of feldspar found in the Columbia Formation. The deposits are heterogeneous both vertically and laterally. The general trend within the formations is a fining upwards of sediment textures. Geomorphology: The Delaware Bay Group deposits are found beneath terraces that have scarps roughly parallel to the Delaware River and Bay tributaries, and relatively flat treads that slope gently toward the modern Delaware Bay.

The Delaware Bay Group includes transgressive deposits consisting of stream, swamp, marsh, estuarine barrier and beach, tidal flat, lagoon, and shallow offshore estuary environments (Ramsey, 1997).

The Delaware Bay Group is comprised of the Lynch Heights Formation, the Scotts Corners Formation, and the Cape May Formation (undivided) in New Jersey. Ramsey (1997) suggested that the Pleistocene interglacial deposits on the New Jersey side of Delaware Bay be included in the Delaware Bay Group. The Cape May Formation has similar geomorphic characteristics, ages, and depositional environments (O’Neal and McGeary, 2002; Newell et al., 2001) to the Delaware Bay Group.

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qdb
Geologic Time Period
upper Pleistocene
Reference(s)

Newell, W.L., Powars, D.S., Owens, J.P., and Schindler, J.S. 2001, Surficial geologic map of central and southern New Jersey: U.S. Geological Survey Miscellaneous Investigation Series Map I-2540-D, scale 1:100,000.

O’Neal, M.L., and McGeary, S., 2002, Late Quaternary stratigraphy and sea-level history of the northern Delaware Bay margin, southern New Jersey, USA: a ground penetrating radar analysis of composite Quaternary coastal terraces: Quaternary Science Reviews, v. 21, p. 929-946.

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Englishtown Formation

Englishtown Formation johncallahan Tue, 07/28/2009 - 13:26

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Light-gray to white, micaceous, slightly silty to silty, fine-grained, slightly glauconitic quartz sand. In outcrop, it is extensively burrowed with Ophiomorpha burrows. Ranges from 20 to 50 ft in thickness. On the cross-section, the Englishtown is shown only where the sands are well developed. Interpreted to be nearshore marine to tidal flat in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
englishtown
Geologic Unit Symbol
Ket
Geologic Time Period
Upper Cretaceous

Hornerstown Formation

Hornerstown Formation johncallahan Tue, 07/28/2009 - 12:15

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconite sand that is silty and slightly to moderately clayey and contains scattered shell beds. Glauconite approximately 90 percent to 95 percent of the sand fraction and quartz 5 percent to 10 percent. Near the top of unit, silt-filled burrows are present. Lower, the unit is commonly laminated with silty sand and moderately clayey sand. Silt and clay matrix is calcareous. Uniformly a dark-greenish-gray. Interpreted to be marine in origin. The Cretaceous-Tertiary boundary is considered to lie within the formation. Rarely occurs in outcrop and where shown on the map is covered by colluvium along the stream valley bluffs. Ranges between 10 and 50 feet in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Hornerstown
Geologic Unit Symbol
KTht
Geologic Time Period
Upper Cretaceous and Paleocene

Ironshire Formation

Ironshire Formation siteadmin Mon, 08/16/2010 - 11:17

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Ironshire Formation was described by Owens and Denny (1979) as consisting of a lower loose, pale-yellow to white, well-sorted, medium sand characterized by long, low-angle inclined beds with laminae of black minerals. The upper portion of the units was described as consisting of light-colored, trough cross-stratified, well-sorted sand with pebbles and a few Callianassa borings. They described the Ironshire Formation near Rehoboth in a stratigraphic section which is now considered to be a part of the Lynch Heights Formation.

Detailed mapping is needed to clearly describe the unit in Delaware. Based on limited investigation in Delaware by the author, the Ironshire Formation is a fine to medium, sugary sand overlying a gray, silty clay that is flaser- to wavybedded with fine to medium sand overlying gray, silty clay with scattered organic-rich laminae in its reference area. To the north toward Indian River Bay, the Ironshire Formation is a fine to medium sand with coarse laminae and scattered pebbles and rare, scattered shelly zones and silty clay beds. The sands are quartzose with less than 10 percent feldspar. The Ironshire Formation is rarely over 20 feet thick.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Ironshire
Geologic Unit Symbol
Qi
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Kent Island Formation

Kent Island Formation siteadmin Mon, 08/16/2010 - 11:41

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

Owens and Denny (1979) named the Kent Island Formation for deposits bordering the Chesapeake Bay found underneath lowlands that ranged in elevation from 0 to 25 feet in elevation but most of the land surface area is less than 10 feet in elevation. These lowlands are bordered by a scarp with at toe at approximately 25 feet. In its type area, the Kent Island Formation was described as consisting of thick beds of loose, light colored, cross-stratified sand overlying dark-colored massive to thinly laminated clay-silt. Pebbles as much as 10 cm (4 in.) in diameter occur in thin beds with the sand or as scattered clasts in both the sand and clay-silt. Locally, large tree stumps in growth position are encased in the clay-silt. Maximum thickness of the Kent Island was about 12 m (40 feet).

The Kent Island Formation in Delaware consists of a lower, light-gray to reddish-brown, coarse sand to pebble gravel with scattered organic silty clay lenses; a middle, gray, clayey silt to silty clay; and an upper fine to medium, brownish-yellow sand with scattered clay laminae. Rare lenses of shell, most commonly the oyster Crassostrea, are found where the middle clay is at its thickest. The thickness of the Kent Island Formation in Delaware ranges from 0 to 25 feet.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Kent-island
Geologic Unit Symbol
Qki
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

Lynch Heights Formation

Lynch Heights Formation johncallahan Mon, 07/27/2009 - 13:36

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Heterogeneous unit of light-gray to brown to light-yellowish brown, medium to fine sand with discontinuous beds of coarse sand, gravel, silt, fine to very fine sand, and organic-rich clayey silt to silty sand. Upper part of the unit commonly consists of fine, well-sorted sand. Small-scale cross-bedding within the sands is common. Some of the interbedded clayey silts and silty sands are burrowed. Beds of shell are rarely encountered. Sands are quartzose and slightly feldspathic, and typically micaceous where very fine to fine grained. Unit underlies a terrace parallel to the present Delaware Bay that has elevations between 50 and 30 feet. Interpreted to be a fluvial to estuarine unit of fluvial channel, tidal flat, tidal channel, beach, and bay deposits (Ramsey, 1997). Overall thickness ranges up to 50 feet.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Heterogeneous unit of light-gray to brown to light yellowish brown, medium to fine sand with discontinuous beds of coarse sand, gravel, silt, fine to very fine sand, and organic-rich clayey silt to silty sand. Upper part of unit commonly consists of fine, well-sorted sand. Small-scale cross- bedding within sands is common. Some interbedded clayey silts and silty sands are burrowed. Beds of shell rarely encountered. Sands are quartzose, slightly feldspathic, and typically micaceous where very fine to fine grained. Unit underlies a terrace parallel to present Delaware River that has elevations between 50 and 30 ft. Interpreted to be a fluvial to estuarine unit of fluvial channel, tidal flat, tidal channel, beach, and bay deposits (Ramsey, 1997). Overall thickness rarely exceeds 20 ft.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Lynch-heights
Geologic Unit Symbol
Qlh
Geologic Time Period
middle Pleistocene
Reference(s)

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Magothy Formation

Magothy Formation johncallahan Tue, 07/28/2009 - 13:30

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Dark-gray to gray silty clay to clayey silt that contains abundant fragments of lignite; grades downward into a very fine to fine sand with scattered and discontinuous thin beds of clayey silt with lignite fragments. Thickness ranges from 20 to 50 ft. Updip in the vicinity of the Chesapeake and Delaware Canal, the Magothy fills channels incised into the Potomac Formation and is discontinuous in its extent. Interpreted to have been deposited in coastal to nearshore environments.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
magothy
Geologic Unit Symbol
Km
Geologic Time Period
Upper Cretaceous

Marshalltown Formation

Marshalltown Formation johncallahan Tue, 07/28/2009 - 13:24

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Greenish-gray, slightly silty, fine-grained glauconitic quartz sand. Glauconite comprises 30 to 40 percent of the sand fraction. Ranges from 10 to 50 ft in thickness. Extensively burrowed. Interpreted to be marine in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
marshallton
Geologic Unit Symbol
Kmt
Geologic Time Period
Upper Cretaceous

Manasquan Formation

Manasquan Formation johncallahan Tue, 07/28/2009 - 13:20

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Consists of 30 ft of silty, shelly, fine sands that are commonly glauconitic (Benson and Spoljaric, 1996). Deposited during the latest Paleocene to early Eocene (Benson and Spoljaric, 1996). Based on microfossils (unpublished DGS file data), it can be characterized as an open shelf deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
manasquan
Geologic Unit Symbol
Tmq
Geologic Time Period
Paleocene to Eocene
Reference(s)

Benson, R.N., and Spoljaric, N., 1996, <a href="/publications/b20-stratigraphy-post-potomac-cretaceous-tertiary-rocks-central-delaware">Stratigraphy of the post-Potomac Cretaceous-Tertiary rocks of central Delaware: Delaware Geological Survey Bulletin 20</a>, 28 p.

Merchantville Formation

Merchantville Formation johncallahan Tue, 07/28/2009 - 13:28

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Light- to dark-gray, very micaceous, glauconitic, very silty fine- to very fine-grained sand to fine sandy silt. Ranges from 20 to 120 ft in thickness. Marine in origin.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
merchantville
Geologic Unit Symbol
Kmv
Geologic Time Period
Upper Cretaceous

Mt. Laurel Formation

Mt. Laurel Formation johncallahan Tue, 07/28/2009 - 12:18

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Slightly calcareous, glauconitic, quartz sand that is medium to fine grained. Contains about 3 to 5 percent glauconite. Sand is subrounded to subangular and slightly silty with a few moderately silty zones. Scattered belemnites are present as well as a few scattered shell fragments or thin shell beds. Uniform dark olive gray or yellowish-brown where weathered. In outcrop, reported to be extensively burrowed (Owens, et al., 1970). Where it is the surficial deposit south of the Chesapeake and Delaware Canal, the Mt. Laurel can be confused with the Columbia Formation, especially where the color is similar. Can be differentiated by ubiquitous presence of glauconite and generally better sorted sands of the Mt. Laurel. Marine in origin. Ranges from 30 to 100 ft in thickness.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Mount-laurel
Geologic Unit Symbol
Kml
Geologic Time Period
Upper Cretaceous
Reference(s)

Owens, J.P., Minard, J.P., Sohl, N.F., and Mello, J.F., 1970, Stratigraphy of the outcropping post-Magothy Upper Cretaceous Formations in Southern New Jersey and Northern Delmarva Peninsula, Delaware and Maryland: U.S. Geological Survey Professional Paper 674, 60 p.

Nanticoke River Group

Nanticoke River Group siteadmin Fri, 08/20/2010 - 12:34

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Nanticoke River Group consists of the Turtle Branch and Kent Island Formations. In Delaware, the Nanticoke River Group extends along the margins of the Nanticoke River and its tributaries. It continues along the Nanticoke River into adjacent Maryland.

The Nanticoke River Group consists of heterogeneous units of interbedded fine to coarse sand, clayey silt, sandy silt, and silty clay. Where the units are muddy, downstream of Seaford, the sequence consists of a lower fluvial to estuarine swamp to tidal stream deposits (coarse sand to gravelly sand with scattered organic-rich muddy beds) overlain by estuarine clayey silts and silty clays that contain rare to common Crassostrea (oyster) bioherms. The silts and clays are overlain by sands with clay laminae, to fine to coarse well-sorted, clean sand that are estuarne beach and eolian in origin. Upstream, the mud beds are rarer and restricted to the west side of streams and consist of organic rich clayey silt. Most of the stratigraphic section is dominated by clean, well-sorted sands.

The Nanticoke River Group consists of fluvial to estuarine, fine to coarse sand and estuarine clayey silts to silty clays that were deposited during highstands of sea level during the late Pleistocene. In Delaware, these deposits underlie terraces that flank the margins of the present Nanticoke River and its tributaries. Upstream the terraces become less distinct, and in places the surface of the Nanticoke River Group does not have a distinctive boundary scarp with the adjacent Beaverdam Formation. The Nanticoke River Group sands, however, are distinct and readily discernable from those of the Beaverdam Formation; the Nanticoke River Group sands are more well sorted, less feldspathic, and lack the distinctive white silty matrix of the Beaverdam Formation.

The informal term “Nanticoke deposits” was used by Andres and Ramsey (1995, 1996) for Quaternary sediments along the Nanticoke River in the vicinity of Seaford in western Sussex County. These deposits included estuarine sediments as well as eolian dunes along the margins of the Nanticoke River. More recent mapping in the Georgetown area in 2006 and 2007 (Ramsey, 2010), as well as along the Nanticoke River to the southwest of Seaford in 2005 (unpublished DGS data), has allowed for more detailed analysis of the deposits and for recognition of two stratigraphic units within what was mapped as the Nanticoke deposits.

Subtitle

Coastal Plain - Primarily Surficial Unit

Geologic Unit Symbol
Qnrg
Geologic Time Period
middle to upper Pleistocene
Reference(s)

Andres, A.S., and Ramsey, K.W., 1995, Geologic Map of the Seaford area, Delaware: Delaware Geological Survey Geologic Map Series No. 9, scale 1:24,000.

_____, 1996, Geology of the Seaford area, Delaware: Delaware Geological Survey Report of Investigations No. 53, 22 p.

Navesink Formation

Navesink Formation johncallahan Tue, 07/28/2009 - 13:22

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Generally a calcareous silt that is slightly to moderately sandy and slightly to moderately clayey. Sand is fine to very fine grained composed of about 50 percent glauconite, 40 percent peloids, and 10 percent quartz. Sediment is laminated, marked by varying amounts of clay and sand. Peloids are yellow to yellowish-brown flat to ovoid pellets that are calcareous and may contain flakes of chitin and grains of glauconite or quartz. Scattered shell fragments are present but form a minor constituent of the sediment. Uniformly dark-greenish-gray, slightly lighter in color than the overlying Hornerstown Formation. 10 to 20 ft thick.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
navesink
Geologic Unit Symbol
Knv
Geologic Time Period
Upper Cretaceous

Old College Formation

Old College Formation johncallahan Tue, 07/28/2009 - 12:05

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Reddish-brown to brown clayey silt, silty sand to sandy silt, and medium to coarse quartz sand with pebbles (Ramsey, 2005). Rock fragments of mica or sillimanite quartzose schist are common sand fraction. At land surface, a gray to grayish-brown clayey silt is present. Sands are cross-bedded with laminae of muscovite or heavy minerals defining the cross-sets. Silty beds tend to be structureless, or in the gray clayey silt beds, heavily bioturbated by roots. No fossils other than pollen have been recovered. Pollen indicate a cold climate during deposition of the upper clayey silt unit (unpublished DGS data). Stratigraphic relationships indicate either slightly younger than or contemporaneous with the Columbia Formation. Ranges from 5 to 40 ft in thickness.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Old-college
Geologic Unit Symbol
Qoc
Geologic Time Period
middle Pleistocene
Reference(s)

Ramsey, K.W., 2005, <a href="/publications/ri69-geology-old-college-formation-along-fall-zone-delaware">Geology of the Old College Formation along the Fall Zone of Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Omar Formation

Omar Formation siteadmin Mon, 08/16/2010 - 11:28

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

The Omar Formation was originally described (Jordan, 1962) as consisting of interbedded, gray to dark gray, quartz sands and silts with bedding ranging from a few inches to more than 10 feet thick. Thin laminae of clay are found within the fine, well-sorted sands. Silt mixed with sand generally contains some plant matter and where dark in color could be considered organic. Sands contain wood fragments, some of which are lignitic.

On the basis of regional mapping by Ramsey (2010), the description of the Omar Formation is modified from that of Jordan (1962). The Omar Formation consists of quartzose, greenish-gray to light-yellow, homogeneous, fine to very fine sand with scattered medium to coarse laminae commonly overlain by dark-greenish-gray, silty clay to clayey silt with scattered shell beds and bioherms of the oyster Crassostrea. The silty clay is overlain by a light-gray, fine to coarse sand. Coarse sand and gravel interspersed with organic-rich horizons that include stumps and logs of cypress trees is found both at the base of the Omar Formation and at the top of the silty clay.

The Omar Formation ranges from 10 to 80 feet thick. In the western portions of its extent in the vicinity of Cypress Swamp and to the north where it grades into the Lynch Heights Formation, the unit is typically a sheet of moderately well sorted to well sorted, fine to coarse sand.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
omar
Geologic Unit Symbol
Qo
Geologic Time Period
middle Pleistocene
Reference(s)

Jordan, R.R., 1962, <a href="/publications/b9-stratigraphy-sedimentary-rocks-delaware">Stratigraphy of the sedimentary rocks of Delaware: Delaware Geological Survey Bulletin No. 9</a>, 51 p.

Piney Point Formation

Piney Point Formation johncallahan Mon, 07/27/2009 - 14:03

Description published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Bright green, fine to coarse, shelly, glauconitic (20 to 40% glauconite), quartz sand. Silty and clayey toward the bottom and coarsens upwards. Considered to be a marine deposit (Benson, Jordan, and Spoljaric, 1985). The Piney Point aquifer coincides with the sandier portion of the unit. Ranges up to 250 feet thick in the southern portion of Kent County.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
piney-point
Geologic Unit Symbol
Tpp
Geologic Time Period
upper Eocene
Reference(s)

Benson, R.N., Jordan, R.R., and Spoljaric, N., 1985, <a href="/publications/b17-geological-studies-cretaceous-and-tertiary-section-test-well-je32-04-central-delawa">Geological study of the Cretaceous and Tertiary Section, Test Well Je32-04, Central Delaware: Delaware Geological Survey Bulletin No. 17</a>, 69 p.

Potomac Formation

Potomac Formation johncallahan Tue, 07/28/2009 - 12:21

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Dark-red, gray, pink, and white silty clay to clayey silt and very fine to medium sand beds. Beds of gray clayey silt to very fine sand that contain pieces of charcoal and lignite are common. Deposited in a fluvial setting in a tropical to subtropical environment as indicated by abundant paleosol horizons. Ranges from 20 ft updip to over 1600 ft thick in southern New Castle County.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
Potomac
Geologic Unit Symbol
Kpt
Geologic Time Period
Cretaceous

Scotts Corners Formation

Scotts Corners Formation johncallahan Fri, 07/24/2009 - 15:25

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Heterogeneous unit of light-gray to brown to light-yellowish-brown, coarse to fine sand, gravelly sand and pebble gravel with rare discontinuous beds of organic-rich clayey silt, clayey silt, and pebble gravel. Sands are quartzose with some feldspar and muscovite. Commonly capped by one to two feet of silt to fine sandy silt. Laminae of opaque heavy minerals are common. Unit underlies a terrace parallel to the present Delaware River that has elevations less than 25 feet. Interpreted to be a transgressive unit consisting of swamp, marsh, estuarine channel, beach, and bay deposits. Climate during the time of deposition was temperate to warm temperate as interpreted from fossil pollen assemblages (Ramsey, 1997). Overall thickness of the unit rarely exceeds 20 feet.



The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Heterogeneous unit of light-gray to brown to light-yellowish-brown, coarse to fine sand, gravelly sand and pebble gravel with rare discontinuous beds of organic-rich clayey silt, clayey silt, and pebble gravel. Sands are quartzose with some feldspar and muscovite. Commonly capped by one to two ft of silt to fine sandy silt. Laminae of opaque heavy minerals common. Unit underlies a terrace parallel to the present Delaware River that has elevations less than 25 ft. Interpreted to be a transgressive unit consisting of swamp, marsh, estuarine channel, beach, and bay deposits. Climate during deposition was temperate to warm temperate as interpreted from fossil pollen (Ramsey, 1997). Overall thickness rarely exceeds 15 ft.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Scotts-corners
Geologic Unit Symbol
Qsc
Geologic Time Period
upper Pleistocene
Reference(s)

Ramsey, K.W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion Quadrangles, Delaware: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Shark River Formation

Shark River Formation johncallahan Tue, 07/28/2009 - 13:18

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconitic clayey silt and clay, with some glauconite sand and fine glauconitic quartz sand. Deposited in the middle Eocene (Benson and Spoljaric, 1996), and is generally 60 to 70 ft thick. Based on the microfossils (unpublished DGS file data), it can be characterized as an open shelf deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
shark-river
Geologic Unit Symbol
Tsr
Geologic Time Period
Eocene
Reference(s)

Benson, R.N., and Spoljaric, N., 1996, <a href="/publications/b20-stratigraphy-post-potomac-cretaceous-tertiary-rocks-central-delaware">Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware: Delaware Geological Survey Bulletin 20</a>, 28 p.

Sinepuxent Formation

Sinepuxent Formation siteadmin Mon, 08/16/2010 - 11:10

The following description was published in RI76 Stratigraphy, Correlation, and Depositional Environments of the Middle to Late Pleistocene Interglacial Deposits of Southern Delaware, Ramsey, K.W., 2010:

Owens and Denny (1979) described the Sinepuxent Formation in Maryland as dark, poorly sorted, silty fine to medium sand with the lower part of the unit being fine grained with thin beds of black clay. The Sinepuxent Formation is described as being lithically distinct from the Omar and Ironshire Formations due to the presence gray, laminated, silty very fine to fine, quartzose, micaceous, sand to sandy silt. The base of the unit is typically a bluishgray to dark-gray clayey silt to silty clay. There are a few shelly zones within the Sinepuxent Formation in the vicinity of Bethany Beach (McDonald, 1981; McLaughlin et al., 2008). The Sinepuxent Formation is up to 40 feet thick.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Sinepuxent
Geologic Unit Symbol
Qsi
Geologic Time Period
late Pleistocene
Reference(s)

Owens, J.P., and Denny, C.S., 1979, Upper Cenozoic deposits of the Central Delmarva Peninsula, Maryland and Delaware: U.S. Geological Survey Professional Paper 1067-A, 28 p.

McDonald, K.A., 1981, Three-dimensional analysis of Pleistocene and Holocene coastal sedimentary units at Bethany Beach, Delaware: unpublished M.S. Thesis, University of Delaware, Newark, 205 p.

McLaughlin, P.P., Miller, K.M., Browning, J.V., Ramsey, K.W., et al., 2008, <a href="/publications/ri75-stratigraphy-and-correlation-oligocene-pleistocene-section-bethany-beach-delaware">Stratigraphy and Correlation of the Oligocene to Pleistocene Section at Bethany Beach, Delaware: Delaware Geological Survey Report of Investigations No. 75</a>, 41 p.

St. Marys Formation

St. Marys Formation johncallahan Mon, 07/27/2009 - 13:52

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Bioturbated, dark-greenish-gray silty clay, banded light-gray, white, and red silty clay, and glauconitic, shelly, very fine sandy silt. In the Georgetown Quadrangle, the St. Marys Formation is capped by about 5 to 15 ft of bioturbated, dark-greenish-gray silty clay. A distinct burrowed horizon separates the clay from the underlying banded clay that consists of a 10- to 15-ft thick, compact, color-banded silty clay with scattered white clayey concretions. The banded clay has a sharp contact at its base with underlying glauconitic, very fine, sandy silt. The sandy silt contains shells of the gastropod Turritella. The entire thickness of the St. Marys Formation is less than 100 ft in the Georgetown Quadrangle, thinning from its thickest in the southeast corner to about 50 ft thick in the northwest corner of the map area. Interpreted to be a marine deposit of late Miocene age (McLaughlin et al., 2008).



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light reddish-brown to gray, fine to very fine, silty sand and clayey silt. Discontinuous beds of fine to medium quartz sand are common. Base of unit in the Milford area (Ramsey, 1997) is a medium sand bed ranging from 10 to 15 feet thick. Found in the southeastern portion of Kent County. Patchy in distribution where it occurs beneath Quaternary deposits. Thickness ranges up to 30 feet. Interpreted to be a shallow marine deposit.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
st-marys
Geologic Unit Symbol
Tsm
Geologic Time Period
upper Miocene
Reference(s)

McLaughlin, P.P., Miller, K.G., Browning, J.V., Ramsey, K. W., and others, 2008,<a href="/publications/ri75-stratigraphy-and-correlation-oligocene-pleistocene-section-bethany-beach-delaware"> Stratigraphy and Correlation of the Oligocene to Pleistocene section at Bethany Beach, Delaware: Delaware Geological Survey Report of Investigations No. 75</a>, 41 p.

Ramsey, K. W., 1997, <a href="/publications/ri55-geology-milford-and-mispillion-river-quadrangles">Geology of the Milford and Mispillion River quadrangles: Delaware Geological Survey Report of Investigations No. 55</a>, 40 p.

Turtle Branch Formation

Turtle Branch Formation johncallahan Mon, 07/27/2009 - 13:39

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Fining-upward sequence of a thin (less than 1 ft thick), gravelly sand, to an interlaminated, medium to coarse sand with heavy mineral laminae, to a well-sorted fine to medium, fluffy sand that makes up the bulk of the unit. Near the present stream valleys, 1 to 5-ft thick beds of light-grayish-brown to brown, organic-rich, clayey silt are common. Along the margins of the unit where it is adjacent to the Beaverdam Formation, the unit commonly consists of pale-yellow to yellowish-brown, fine to very fine silty sand. The unit is less than 5 ft thick over much of its mapped area but can range up to 20 ft thick near the present stream valleys. The well-sorted sands of the Turtle Branch Formation are differentiated from those of the dune deposits by their slightly coarser texture, better developed soil profile, and common presence of heavy mineral laminae. Interpreted to be a sand-dominated fluvial to tidal and shoreline deposit associated with a high stand of sea level during the middle Pleistocene.



The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

One to five feet of gray coarse sand and pebbles overlain by one to ten feet of tan to gray clayey silt to silty clay that is in turn overlain by three to five feet of fine to medium sand. Laterally, finer beds are less common away from Marshyhope Creek and the deposit is dominated by fine to medium sand with scattered beds of coarse to very coarse sand with pebbles. Sands are quartzose with some feldspar and laminae of opaque heavy minerals. Underlies a terrace with elevations ranging from 35 to 50 feet and is interpreted to be fluvial to estuarine in origin. Found in the Marshyhope Creek drainage basin in Kent County and more extensively along the Nanticoke drainage basin in Sussex County. Thickness ranges up to 20 feet closer to the valley of the Marshyhope and thins away from the river.

Subtitle

Coastal Plain - Primarily Surficial Unit

Formation Type
Turtle-branch
Geologic Unit Symbol
Qtb
Geologic Time Period
middle Pleistocene

Vincentown Formation

Vincentown Formation johncallahan Tue, 07/28/2009 - 12:12

The following description was published in GM13 Geologic Map of New Castle County, Delaware, Ramsey, K.W., 2005:

Glauconitic sand that ranges from slightly silty to moderately silty and slightly to moderately clayey. Dominant constituent is subrounded to subangular clear quartz sand that ranges from medium to fine grained. Fine-grained glauconite is a secondary constituent, which ranges from 5 percent in the clayey zones to 15 percent where cleaner. Towards bottom of unit, glauconite percentages increase to about 50 percent of the sand fraction. Silty and clayey zones are thin to thick laminae ranging from 0.01 to 0.5 ft thick. Olive gray to dark-yellowish-brown in zones where iron cement is present. Interpreted to be marine in origin. Rarely occurs in outcrop and is covered by colluvium along the stream valley bluffs where shown on the map. Ranges from 50 to 100 ft in thickness in the subsurface and less than 50 ft thick where it is cut by younger deposits updip.

Subtitle

Coastal Plain - Primarily Subsurface Unit

Formation Type
vincentown
Geologic Unit Symbol
Tvt
Geologic Time Period
Paleocene

Hydrogeology

Hydrogeology johncallahan Thu, 06/24/2010 - 23:53

Introduction to the Hydrogeology of Delaware

Introduction to the Hydrogeology of Delaware johncallahan Sat, 06/27/2009 - 00:19
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Delaware’s water, both ground and surface, is one of its most important natural resources. It is essential for meeting the needs of all segments of our society and for maintaining economic growth and agriculture. At this time, all water used for public and domestic supply and more than 98% of water used for irrigation south of the Chesapeake and Delaware Canal is groundwater. North of the canal, approximately 70% of public water supplies are obtained from four surface-water sources (creeks) and 30% from groundwater resources.

Because of the importance of groundwater to the State, hydrogeologic programs and studies are a major focus of DGS staff. Recent and ongoing efforts include such subjects as ambient and targeted groundwater level and quality monitoring, mapping of aquifer extents and hydraulic properties, assessing the impacts of artificial drainage and wastewater disposal practices, developing methods for remote sensing of groundwater discharge areas, and development of techniques for storage, analysis, and distribution of groundwater information by geographic information systems.

The DGS is the lead agency for collection and analysis of data on groundwater levels and stream discharges in Delaware. The importance of water conditions monitoring has been highlighted in the last several years by a series of droughts and floods. We operate and monitor a variety of systems that provide water-conditions data and capture these data in an Oracle-based hydrological data management system. Groundwater conditions are monitored by a statewide water-level monitoring network of 69 wells. In addition, in 1985 the DGS implemented a water level and chloride monitoring program for 25 wells along the Atlantic Coast to evaluate the potential for salt-water intrusion in aquifers used for public and domestic water supplies. Surface-water conditions are tracked for 15 stream-gage and 10 tide-gage stations around the state. The stream-gaging network was begun by the USGS in 1931 and is now operated cooperatively between the DGS and the USGS.

DGS staff participate in programs and projects related to surface water resources of Delaware and the Delaware River Basin. For example, the DGS coordinates these efforts for the state and facilitates acquisition of streamflow and tide-gage data for Delaware stakeholders. Staff members have also been principal investigators in multi-disciplinary, multi-agency studies to evaluate the fluxes of water, plant nutrients, and other dissolved and suspended sediments in the Inland Bays and Nanticoke River watersheds. As Delaware’s lead earth science agency, the Delaware Geological Survey provides information to inform and educate resource managers and the public to better understand and manage our water resources. The Delaware Geological Survey, by statute, manages and provides liaison for all state-federal projects related to the DGS-USGS Joint-Funded and Partnering Programs.

Data and Graphs about Water in Delaware

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Delaware's Water Budget

Delaware's Water Budget johncallahan Thu, 07/23/2009 - 12:34
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Because of its "renewability" water is unique among earth resources that sustain and enhance life. No other mineral resource that we extract on a long-term and continuous basis can be counted on for at least some degree of replenishment within a human lifetime. This attribute allows a great deal of flexibility in management of the resource. In Delaware local rainfall, approximately 44" to 46" per year, renews part or all of our water supply on a regular basis. However, not all of the rain that falls is available for use. From this total rainfall must be subtracted the water that evaporates (about 20"/year), the amount that is used by plants (about 3 to 6"/year), and the amount that runs overland to surface streams during storms (about 4 to 5"/year). The remainder, approximately 13" to 15" is Delaware's bank of water for the year. This water is stored in a system of groundwater reservoirs, or aquifers, that underlie most of the state. Not only do these groundwater reservoirs provide water to wells, but thyey also maintain the flow in surface streams during times of no rainfall. Streamflow between rainfall events is nothing more than the discharge of excess groundwater.

How much water is there?
Water Equivalents
Inches/Year Billion Gallons/Day
44 4.2
26 2.5
18 1.7
14 1.3
4 0.4

Precipitation: Condensed water vapor that falls to the Earth's surface. Most precipitation occurs as rain, but also includes snow, hail, and sleet.

Runoff: The variety of ways by which water moves across the land. This includes both surface runoff and direct runoff. As it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

Infiltration: The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

Groundwater Flow: The flow of water underground, in the vadose zone and aquifers. Subsurface water may return to the surface (e.g. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

Evaporation: The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration.

Transpiration: The release of water vapor from plants and soil into the air.

Coastal Plain Hydrostratigraphic Chart

Coastal Plain Hydrostratigraphic Chart johncallahan Thu, 01/28/2010 - 16:32
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The following table displays the correlation of hydrologic units to geologic units recognized by the Delaware Geological Survey in the Atlantic Coastal Plain.

Delaware Hydrologic Stratigraphic Chart

Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08

Effect of tropical storms Irene and Lee on groundwater levels in well Qb35-08 andres Tue, 01/10/2012 - 11:51
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Groundwater levels recorded in Qb35-08, a 14-foot deep monitoring well located approximately 5 miles west of Laurel, DE show a remarkable response to tropical storms Irene and Lee, which occurred in August and September, 2011, respectively. Groundwater levels and temperatures in Qb35-08 were collected with an automated pressure-temperature datalogger system. At the same time, rainfall and soil moisture data were recorded by the DEOS Laurel Airport station located approximately 5 miles from the well. In the following illustrations daily mean groundwater levels and groundwater temperatures, total daily rainfall, and daily maximum volumetric soil water content are plotted to show how groundwater,
rainfall, and soil moisture are related.

Note the two big storms were 6.6 (Irene, August 27-28) and 3.7 (Lee, September 8) inches. In response, groundwater level (gwl) rose more than 9-1/2 feet, with the largest rise occurring after the second storm. Though a 9-1/2- foot rise in groundwater level within a few weeks’ time is remarkable, long term the gwl are within the range of previously observed gwl. The shallowest groundwater levels observed in this well, about 3 feet below land surface, are very common in this part of Delaware and a primary reason why there are very few homes with basements in the area. Daily mean groundwater temperatures do not show a noticeable affect from the storm events.

The timing and magnitude of groundwater level rise is related to the rainfall amount and the antecedent maximum daily volumetric water content (VWC) or soil moisture conditions. Prior to the first storm VWC was less than 0.1 indicating a significant soil moisture deficit. Increase of VWC to values above 20 percent (0.2) and onset of gwl rise appear to be strongly correlated with a delay of one day or less. Rates of increase in gwl slow within two days and reverse within 3-4 days after the VWC drops below 20 percent. The rapid rates of rise in VWC and gwl reflect rapid infiltration and groundwater recharge and are consistent with the sandy soil at the DEOS station and sandy aquifer material at the well site. Rapid recharge is one reason why the shallow aquifer is especially vulnerable to pollution from contaminants released at or just beneath land surface.

These data provide an example of why it is important to monitor groundwater conditions. Well Qb35-08 is operated by the Delaware Department of Agriculture as part of their Pesticide Compliance Monitoring Network (PCMN, http://dda.delaware.gov/pesticides/gwater.shtml). Construction, maintenance, and instrumentation are done in cooperation with the Delaware Geological Survey. Additional groundwater and well data can be obtained from this web site or from the PCMN web site.

Latitude
38.55
Longitude
-75.71

The Delaware Water Conditions Summary

The Delaware Water Conditions Summary johncallahan Thu, 09/02/2010 - 12:26
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The Water Conditions Summary is an online monthly summary of water conditions in Delaware. Principal factors in determining water conditions are precipitation, streamflow, and groundwater levels in aquifers. Data from rain gages, stream gages, and observation wells located throughout Delaware have been collected and compiled since the 1960s by the Delaware Geological Survey. These data are displayed as hydrographs and are also available for download. In general, water is abundant in Delaware, but supply is restricted by natural geologic conditions in some areas, by contamination in others, and is dependent on precipitation.

Delaware Geological Survey - US Geological Survey Stream and Tide Gaging Program

Delaware Geological Survey - US Geological Survey Stream and Tide Gaging Program johncallahan Tue, 06/06/2017 - 11:33
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The US Geological Survey in cooperation with the Delaware Geological Survey through a State-Federal partnership program operates and maintains stream and tide gages throughout Delaware. The streamgage network is a component of the National Streamflow Information Program (NSIP), a program that provides real-time and long-term current and historical streamflow information that is not only accurate and unbiased, but also meets the needs of many users.

Although not part of the NSIP, the tide gages also provide real-time and historical information. In 2010, we operate and maintain (24 hours a day, 365 days per year) 13 long-term, continuous-record, real-time streamgages and 2 streamgages that support specific short-term projects. The tide gage network consists of 9 long-term, real-time tide gages and 1 tide gage that supports a specific short-term project. Three streamgages and three tide gages also provide water quality information. Stream and tide gage information are available at http://waterdata.usgs.gov/de/nwis/current/?type=flow.

Stateside funding support for operation and maintenance of this partnership program is provided by the Delaware Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Emergency Management Agency, City of Wilmington, City of Newark, and United Water Delaware. The USGS provides match funding for the streamgage portion of the program.

The Delaware Stream and Tide Gage network provides the hydrologic and water quality information necessary to aid in defining, using, and managing Delaware’s invaluable surface and groundwater resources. The data are used for a multitude of purposes, including, but not limited to, long-range water resources planning and management, short-term resource management, evaluation of drought-no drought conditions, allocation of water resources for public, industrial, commercial, and irrigation water supplies, flood forecasting and warning, bridge and culvert design, hazard spill response and mitigation, analysis of sea level rise, recreation, and floodplain mapping. The stream and tide data are also utilized in existing real-time early warning systems related to potential flooding, and storm/coastal erosion throughout Delaware. The warning systems are used by the DGS, Delaware Emergency Management Agency, all three county emergency management offices, most municipalities, the National Weather Service, the Office of the State Climatologist, and others.

The network is directly tied into the Delaware Environmental Observing System (DEOS) Environmental Monitoring and Observing Network, a network of approximately thirty new meteorological observation sites coupled with existing weather and other environmental observation sites in and around Delaware (http://www.deos.udel.edu).

Mineral Resources

Mineral Resources johncallahan Thu, 06/24/2010 - 23:44

Minerals in Delaware

Minerals in Delaware johncallahan Sat, 06/27/2009 - 00:22
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The description and identification of minerals in Delaware dates from the first quarter of the nineteenth century. During this time, both geologists and amateur mineral collectors have published on the minerals of Delaware including George Carpenter, Issac Lea, James Booth, and Henry duPont. The location of most mineral occurrences in the state occurs in the Delaware Piedmont. This area is comprised on mafic and felsic gneisses and amphibolites of the Wilmington Complex and the metasedimentary gneisses in the Wissahickon, Cockeysville, and Setters formations as well as the migmatitic gneisses and amphibolites of the Baltimore gneiss. The coastal plain contains relatively few mineral localities. These occurrences can be generally divided into those of the oxidizing or oxygen-rich environments of deposition yielding iron oxide deposits and those of reducing or oxygen-poor environments of deposition yielding iron sulfides, phosphates, and carbonates in greensand and organic muds.

(Taken from “Minerals of Delaware” by Peter B. Leavens, in 1979, Transactions of the Delaware Academy of Science, 1976, Delaware Academy of Science, Newark, Delaware).

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Catalog of Delaware Minerals

Catalog of Delaware Minerals johncallahan Fri, 01/15/2010 - 14:26
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More Information:

For specific local information about Delaware Minerals, please refer to the Delaware Mineralogical Society, especially to their Mineral of the Month!

Special Note

Invalid Mineral Names and Mineral Symbols (per IMA/CNMMN)

  • bronzite = var. of enstatite
  • canbyite = hisingerite
  • deweylite = mixture of layer silicates
  • fibrolite = sillimanite
  • garnierite = probably nepouite
  • hornblende = amphibole group
  • eucoxene = most likely anatase or rutile
  • limonite = most likely goethite
  • marmolite = most likely chrysotile or lizardite (serpentine group)
  • picotite = chrome spinel
  • psilomelane = probably romanechite
  • serpophite – most likely lizardite (serpentine group)
  • wad = mixture of Mn oxides/hydroxides

 

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Glauconite (Greensand)

Glauconite (Greensand) johncallahan Mon, 07/20/2009 - 14:21
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Greensand is composed primarily of the mineral glauconite -- a potassium, iron, aluminum silicate. In some Delaware greensands, the glauconite content exceeds 90%. The remaining 10% is mainly quartz. In the past, greensand was used in Delaware as an inexpensive fertilizer. The only active greensand mine in the U.S. today is in New Jersey. Once mined, greensand is dried and used as a soil conditioner. Greensand is also used in water softeners primarily to remove iron from the water. Recent research has shown that greensand has the potential for use as a filter of heavy metals from industrial waste water and landfill leachates.

Sand and Gravel

Sand and Gravel johncallahan Mon, 07/20/2009 - 14:16
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Sand and gravel are essential for supporting and maintaining economic development throughout Delaware. These natural resources are used primarily for aggregate in the productions of concrete for residential, commercial, and industrial buildings, bridge and highway construction, fill for road beds and foundations, water and wastewater treatment facilities, and for replenishment of our Atlantic and Delaware Bay beaches.

There are relatively large quantities of sand and gravel in Delaware. Most of these resources occur as surficial or near-surface deposits that form a veneer of sand and gravel with a thickness up to 150-200 ft in the Delaware Coastal Plain. The deposits generally thicken from north to south across Delaware. However, the quantity and quality of the sand and gravel deposits is not evenly distributed throughout Delaware. There are significant quantities of sand deposits in Delaware Bay and off Delaware’s Atlantic Coast that have been and will be used for beach replenishment (DGS Report of Investigations No. 63 An Evaluation of Sand Resources, Atlantic Offshore, Delaware).

The U.S. Geological Survey in cooperation with the Delaware Geological Survey compiles sand and gravel production information on an annual basis and reports it in U. S. Geological Survey publication entitled "The U.S. Geological Survey Minerals Yearbook, The Mineral Industry of Delaware." (http://minerals.usgs.gov/minerals/pubs/state/de.html). At this time, there are at least 11 major sand and gravel production operations in Delaware. General locations are shown on the map. The USGS reported that approximately 3.64 million tons of sand and gravel valued at about $24.7 million dollars were mined in Delaware in 2007. The DGS estimates that the quantities of sand and gravel produced from the State’s natural resources are typically higher than those reported by the USGS. Reasons for this include: (1) not being certain that all major producers report production to the USGS; (2) state and local government agencies or companies that produce from borrow pits for their own use do not report production; (3) some operations that mine relatively small amounts of sand and gravel may not have been contacted, and, therefore, do not report production; and (4) production of sand from offshore areas for beach replenishment is not included in USGS figures. For example, according to the Delaware Department of Natural Resources and Environmental Control, in 2004 and 2005 approximately 4.4 million tons of sand with an estimated value of $20.3 million was dredged from the Delaware Bay and Atlantic Ocean and placed on beaches along the Delaware Bay and Atlantic Coast.

For more general information related to sand and gravel production and use, the reader may refer to American Geological Institute Environmental Series No. 8 entitled "Aggregates and the Environment." This publication provides the general public, educators, and policy makers a better understanding of the aggregates and environmental concerns related to aggregate resources and supplies (http://www.agiweb.org/environment/publications/aggregate.pdf).

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Natural Hazards

Natural Hazards johncallahan Fri, 06/25/2010 - 09:38

Natural Hazards in Delaware

Natural Hazards in Delaware johncallahan Mon, 07/13/2009 - 14:19
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Natural hazards are those events in the physical environment that present risks to human life or property. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising emergency management agencies on natural hazards, and are included in the Delaware Emergency Operations Plan as an agency having a vital role in dealing with floods, northeaster/extratropical storms, droughts, earthquakes, sinkholes, and dam failures.

Because of the risk of coastal flooding in southern Delaware, the DGS conducts a program to document the effect of tides and winds on coastal erosion, especially for events with potentially large human impact. One effort as part of this program was a study of historical accounts of the effects of a Category 1 hurricane that swept northward from the Outer Banks of North Carolina, hitting Delaware on October 23, 1878. A storm surge in Delaware Bay raised water levels 6 feet in one hour in some areas, and the highest water levels in the Delaware River at Wilmington were as much as 12 feet above present sea level. More than 100 fatalities were attributed to the hurricane and property damage may have been as much as $150 million in today’s currency. This storm may well be the hurricane of record for the Delaware region and provides a worst-case scenario for a modern hurricane.

Northeasters are a natural hazard that affects Delaware. Northeasters are storms with galeforce or stronger winds from the northeast generated by low-pressure systems offshore the U.S. eastern seaboard. These generate storm waves that can result in significant beach erosion. The duration of the storm is considered a critical factor in the severity of the erosion. Two severe northeasters between January 26 and February 6, 1998 brought tropical storm-force wind gusts to the Delaware coast. They produced the third and fourth highest tides measured at Breakwater Harbor near Lewes, high tides of record at the Coast Guard Station at Indian River Inlet and along Indian River at Rosedale Beach, and 20-ft-high waves at a buoy offshore the Delaware-Maryland state line, which caused some overwash of coastal dunes and localized coastal flooding. Few structures were damaged. In contrast, the severity of these storms is dwarfed by the devastating northeaster of March, 1962. Overwash was pervasive along the entire length of the coast; few sand dunes were left intact and barrier islands were essentially flattened. Most structures adjacent to the beach were damaged. However, tides were comparable for these storms; the 1962 storm had five successive high tides that were well above normal, yet the February 1998 storm had several high tides at similar levels as well as low tides that were higher than those of the 1962 storm. The difference in destruction at similar tide levels suggests that wave conditions may have been more severe in the 1962 storm. Given the extensive development of the coastline since 1962, a storm of similar magnitude would today likely cause damage in the billions of dollars and potentially result in human casualties.

Assessment of storm event risks and response strategies depends, in part, on a sound understanding of hydrology and geology. The coastal regions of southern Delaware are impacted by coastal erosion and flooding during large storms, and the Piedmont of northern Delaware is susceptible to flash flooding during major rain events. The DGS serves on the Delaware Emergency Management Agency’s (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and usually have staff located at the Delaware Emergency Operations Center during storm emergencies. We have recently been involved in the development of the Delaware Environmental Observation System in cooperation with DEMA and the Office of the State Climatologist. As part of this, a Coastal Flood Risk Analysis System has been proposed that will integrate stream-flow and tide-gage data with meteorological information in a network to be used for real-time flood analysis/prediction and emergency planning, response, and recovery operations. Other natural disaster-related activities include the DEMA Northeaster Task Force, the DEMA Technical Assessment Center for Natural Disasters, the DEMA State Hazard Mitigation Team, and advising on development of a statewide Dam Safety Program.

Earthquakes are a natural hazard that occur in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677, and 69 earthquakes have been documented or suspected in Delaware since 1871. Although Delaware does not face the same degree of earthquake hazard as other, more seismically active parts of the county, FEMA and the USGS in 1997 reclassified Delaware from a low seismic risk to a moderate seismic risk. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). In the memory of many Delawareans is the 1973 earthquake, which was a magnitude 3.8 temblor (Modified Mercalli VVI).

Another hazard studied by the DGS is sinkholes. Geologic mapping in the Hockessin area shows an area underlain by marble and other carbonate bearing rocks that are particularly susceptible to sinkhole formation. At the request of the New Castle County government, DGS staff regularly review consultants’ reports related to proposed construction activities in carbonate areas. We also have visited and educated concerned citizens when sinkholes have appeared on their property. Our input helps guide the development of relevant ordinances related to land-use planning and construction activities in these areas.

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Earthquakes

Earthquakes johncallahan Fri, 06/25/2010 - 09:45

Overview of Earthquakes in Delaware

Overview of Earthquakes in Delaware johncallahan Sat, 06/27/2009 - 00:10
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Every year approximately 3,000,000 earthquakes occur worldwide. Ninety eight percent of them are less than a magnitude 3. Fewer than 20 earthquakes occur each year, on average, that are considered major (magnitude 7.0 – 7.9) or great (magnitude 8 and greater). Between 2000 and 2009, the United States experienced approximately 32,000 earthquakes; six were considered major and occurred in either Alaska or California (http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php#tabl…).

Earthquakes do not occur exclusively in the western United States. Seven events with magnitudes greater than 6.0 have occurred in the central and eastern sections of the United States since 1811 (http://earthquake.usgs.gov/earthquakes/states/historical_mag.php). Of these, four occurred near New Madrid, Missouri between 1811 and 1812, and one occurred in Charleston, South Carolina, in 1886. The largest event in Delaware occurred in 1871 and had an estimated magnitude 4.1. The largest recorded event in Delaware occurred in 1973 and had an estimated magnitude of 3.8.

In 1997, Delaware was reclassified from being a low seismic risk state to being a medium seismic risk state by the U.S. Geological Survey (USGS) and the Federal Emergency Management Agency (FEMA).

The Delaware Geological Survey (DGS) currently operates a network of five seismic stations throughout Delaware. Fifty-eight earthquakes have been documented in Delaware since 1871. Refer to Baxter (2000) and http://www.dgs.udel.edu/datasets/catalog-delaware-earthquakes-spreadshe… for more details about the DGS Seismic Network, Delaware Earthquake Catalog, and for documentation of earthquakes.

An earthquake occurred in Delaware on October 9, 1871, and caused severe property damage. In Wilmington, Delaware's largest city, chimneys toppled, windows broke, and residents were quite bewildered by the unusual event. Lighter damage was sustained in northern Delaware at Newport, New Castle, and in Oxford, Pennsylvania. Earth noises, variously described as "rumbling" and "explosive," accompanied the shock in several areas.

A tremor in March 1879 beneath the Delaware River, not far from Dover, was felt "strongly" in that area according to old seismic records. The records, however, do not describe the "strong" effects.

On May 8, 1906, a shock occurred in Delaware just three weeks after the noted San Francisco earthquake in California. Records state this shock was strong at Seaford, in southwest Delaware, but list no details concerning the event.

Two tremors, both below intensity V, occurred in Delaware, one on the Lower Delaware in December 1937, and one near Wilmington in January 1944.

Parts modified from Earthquake Information Bulletin, May - June 1971, Volume 3, Number 3.

More Information

More information about the frequency, locations, and science of earthquakes can be found in the adjacent pages on this site and in the DGS report: Special Publication 23: Earthquake Basics.

Latitude
39.57
Longitude
-75.65
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Catalog of Delaware Earthquakes Spreadsheet

Catalog of Delaware Earthquakes Spreadsheet rockman Fri, 07/31/2009 - 15:11

The occurrences of earthquakes in northern Delaware and adjacent areas of Pennsylvania, Maryland, and New Jersey are well documented by both historical and instrumental records. Over 550 earthquakes have been documented within 150 miles of Delaware since 1677. One of the earliest known events occurred in 1737 and was felt in Philadelphia and surrounding areas. The largest known event in Delaware occurred in the Wilmington area in 1871 with an intensity of VII (Modified Mercalli Scale). The second largest event occurred in the Delaware area in 1973 (magnitude 3.8 and maximum Modified Mercalli Intensity of V-VI). The epicenter for this event was placed in or near the Delaware River. Sixty-nine earthquakes have been documented or suspected in Delaware since 1871.

Publication Date
Spatial Reference System(s)
NAD83
Web Map Service (WMS) Information
Update Status
As Needed
Primary Data Category
Geology
Preview
Latitude MAX
39.85
Latitude Min
38.40
Longitude Max
-75.80
Longitude Min
-75.00

Earthquake Felt Report

Earthquake Felt Report johncallahan Thu, 07/30/2009 - 10:39
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Did you feel an earthquake? If so, please complete our Earthquake Felt Report below.

Please answer every question to the best of your ability. Either fill in the blanks where called for or check the response that best describes the event. If a particular question does not apply or if you don't know how to respond, simply skip it and go on to the next. You can review and modify answers to all the questions at any time. Feel free to include any additional information in the Additional Comments box at the end of this form.

The Earthquake of August 23, 2011

The Earthquake of August 23, 2011 johncallahan Tue, 08/23/2011 - 22:58
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Delaware and surrounding areas experienced an earthquake event on the afternoon of Tuesday, August 23, 2011. According to the US Geological Survey, a magnitude 5.8 earthquake struck at 1:51 p.m. in central Virginia, in an area referred to as "the Central Virginia Seismic Zone" because of its relatively active earthquake activity for the region. The epicenter was located five miles south-southwest of Mineral, Virginia, with the quake was focused at a depth of 6 km (3.7 miles) below the surface. The Virginia Geological Survey reports that this is the largest Virginia earthquake known in historic times. A few small aftershocks have occurred in the hours afterward. (http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/se082311a.html)

How was this earthquake felt in Delaware?

In Delaware, the earthquake was felt in many locations from northernmost New Castle County to coastal and inland Sussex County. The Delaware Geological Survey website had "felt reports" completed by more than 300 respondents as of 5:00 pm on Aug 23 and over 500 respondents by the evening of Aug 24 (thank you to all of you who replied!). Preliminarily, these responses indicate a Mercalli Intensity of III to IV. The average intensity of building shaking reported by respondents was "moderate." The majority of respondents noted movement or shaking of furniture such as, bookcases, chairs, and computer equipment, some window shaking, and a few overturned items such as picture frames, bottles, and sculptures.

As of 4:00 pm, the US Geological Survey website had received reports from 108 individuals in Delaware with an average intensity reply of 3.3, so between Mercalli III and IV. In the area of central Virginia near the earthquake epicenter, intensities of VII or "Very Strong" were reported, a level strong enough to make standing difficult and to damage poorly built structures. The USGS also received numerous responses from throughout the eastern United States.

How is the strength of an earthquake measured?

The intensity can be gauged using the Mercalli intensity scale, which is characterized by how a quake feels to the observer. A Mercalli intensity of III is considered "Slight." It is felt by people indoors, especially on the upper floors of buildings. A Mercalli intensity of IV is termed "Moderate". It is felt indoors and, by some people, outdoors. Dishes and windows are commonly disturbed and rattle; it may give the sensation of a heavy truck striking a building. These two categories fit most of our reports from Delaware.

The Richter scale measures the energy released by an earthquake. Geophysical sensors called seismometers measure the amount of shaking of the ground at numerous locations; in Delaware, we have five seismic stations that cover all three counties. The August 23 temblor fell in the upper end of the Moderate strength range, between Richter magnitudes 5.0 and 5.9. An interesting fact to remember about the Richter scale – an increase of one number, such as from 5 to 6, means a 10-time increase in the amplitude of shaking and 33-time increase in energy released. This 5.9 event had considerably more energy than the magnitude 3.8 quake that occurred in Delaware in 1973.

Why did this earthquake occur?

The Virginia Geological Survey notes that the earthquake activity in the area is associated with old faults related to movements of the earth’s tectonic plates related to ancient mountain building episodes that were followed by the opening of the Atlantic Ocean about 150 million years ago. The opening of the Atlantic Ocean was accompanied by cracking of the earth's crust, or faulting, along eastern North America. Since the period of this rifting ended, the east coast has been fairly quiet tectonically, in contrast with the tectonically active western coast of the United States. Nevertheless, there are areas that still experience a gradual accumulation of tectonic stress that is occasionally released in the form of an earthquake.

Why did we feel this earthquake in Delaware so far from its central Virginia source?

The geology of the Middle Atlantic region of the east coast favors the travel of earthquake energy for great distances. The earthquake epicenter was located in the Virginia Piedmont, an area underlain by hard basement rocks that predate the opening of the present-day Atlantic Ocean. To the west lie ancient hard rocks of the Appalachian Mountains. To the east, the hard basement rocks are overlain by a blanket of softer sediments that thickens toward the Atlantic Ocean. The hard basement rocks of our region have been in generally the same configuration, with gradual sinking, for the last 150 million years. Earthquake energy can travel well through these hard, cold ancient rocks, in contrast with areas such as California where there is abundant faulting and softer rocks, which absorb the energy more quickly.

The DGS will update this page with additional information, as it becomes available, on the earthquake of August 23, 2011.

Links

Reference(s)

Earthquake intensity map from the US Geological Survey at http://earthquake.usgs.gov/earthquakes/dyfi/events/se/082311a/us/index…

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USGS Real-time Earthquakes Map

USGS Real-time Earthquakes Map johncallahan Mon, 02/15/2010 - 11:02
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The above map shows M1+ earthquakes that occurred in the past 7 days. This data stream is served by the United States Geological Survey. However, the seismic observations are collected from numerous organizations withing the US and around the world. The Delaware Geological Survey is a contributing agency and maintains its own seismic network.

More resources on current earthquake monitoring

DGS Seismic Network

DGS Seismic Network johncallahan Fri, 06/25/2010 - 09:52

Seismic Network Map

Seismic Network Map johncallahan Thu, 07/30/2009 - 11:10
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The DGS maintains its own network of seismometers to detect local earthquake activity. Following an earthquake swarm in 1972, the DGS established its first seismometer station in Newark. The network now consists of five seismic stations spread across the state: three stations in the Newark-Wilmington area, one at the DEMA office in southern New Castle County, and one at the Sussex County Emergency Operations Center. Signals are recorded on paper and captured digitally using Earthworm, a seismic processing system developed by the USGS. These records are shared nationally through participation in the Advanced National Seismic System Network, the Lamont-Doherty Cooperative Seismographic Network, the Northeast U.S. Seismic Network, and the Southeast U.S. Seismic Network. Small local earthquakes and larger earthquakes from other parts of the country and the world are clearly resolved by the network.

Bellevue State Park (BVD) Seismic Station

Bellevue State Park (BVD) Seismic Station johncallahan Tue, 07/28/2009 - 00:49
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The seismometer located at Bellevue State Park is placed on the Brandywine Blue Gneiss. The Brandywine Blue Gneiss is the new name given to the granulite-facies felsic gneisses in the Wilmington Complex. Informally called the “blue rocks,” this unit is a medium- to coarse-grained, lineated (pinstriped), two-pyroxene gneiss with variable quartz content and thin, discontinuous mafic layers, pods, and schlieren. The pinstriping and the massive nature of the rock suggest the rock is intrusive; however, deformation and recrystallization have obscured original igneous features.

The unit appears on the Wilmington North, Wilmington South, and Marcus Hook quadrangles where it underlies the city of Wilmington and its northeastern suburbs.



Seismometer:Mark Products L-4C Short period Vertical
Amplifier: Sprengnether AS-110 Gain 68dB
VCO: TC-10 1700 Hz

Latitude: 39.77472
Longitude: -75.49944
Elevation: 58 meters above sea level

Elevation
58 meters above sea level
Latitude
39.77
Longitude
-75.50
Longitude2
-75.50
geolocation

39.77472, -75.49944

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Brandywine Creek State Park (BWD) Seismic Station

Brandywine Creek State Park (BWD) Seismic Station johncallahan Tue, 07/28/2009 - 00:59
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The seismometer located at Brandywine Creek State Park is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.

The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East quadrangles.


Seismometer: HS101-A Short period Vertical
Amplifier: Emtel 6243 Gain 36dB
VCO: 2720 Hz

Latitude: 39.79944
Longitude: -75.57667
Elevation: 63 meters above sea level

Elevation
63 meters above sea level
Latitude
39.80
Longitude
-75.58
Longitude2
-75.58
geolocation

39.79944, -75.57667

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Delaware Emergency Management Agency (DEMA) Seismic Station

Delaware Emergency Management Agency (DEMA) Seismic Station johncallahan Tue, 07/28/2009 - 14:23
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The seismometer, located at the Delaware Emergency Management Agency, is located on the Columbia Formation. The Columbia Formation is a fine to coarse, feldspathic quartz sand with varying amounts of gravel. It is primarily a body of glacial outwash sediment deposited in a cold climate during the middle Pleistocene.

Seismometer:Geospace Corp. HS-10 Short period
Amplifier: Emtel 6242 Gain -18dB
VCO: 2380 Hz




Latitude: 39.31871
Longitude: -75.60979
Elevation: 14 meters above sea level

Elevation
14 meters above sea level
Latitude
39.32
Longitude
-75.61
Longitude2
-75.61
geolocation

39.31871, -75.60979

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Sussex County Emergency Operation Center (SCOM) Seismic Station

Sussex County Emergency Operation Center (SCOM) Seismic Station johncallahan Tue, 07/28/2009 - 14:30
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The seismometer, located on the property of the Sussex County Emergency Operation Center, is positioned on the Beaverdam Formation. The Beaverdam Formation is a very coarse sand with beds of fine to medium sand. It is interpreted to be a Pliocene fluvial to estuarine deposit.

Seismometer: Geospace Corp HS-10-1/B Short period Vertical
Amplifier: Emtel 6242 Gain -18dB
VCO: 1020 Hz




Latitude: 38.69567
Longitude: -75.36271
Elevation: 15 meters above sea level

Elevation
15 meters above sea level
Latitude
38.70
Longitude
-75.36
Longitude2
-75.36
geolocation

38.69567, -75.36271

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White Clay Creek State Park (NED) Seismic Station

White Clay Creek State Park (NED) Seismic Station johncallahan Tue, 07/28/2009 - 13:58
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The seismometer, located in White Clay Creek State Park, is positioned on the Wissahickon Formation. The Wissahickon Formation is an extensive sequence of pelitic and psammitic gneisses interlayered with amphibolites. With few exceptions, most of the amphibolite layers are less than 30 feet thick. The rocks have been metamorphosed to upper amphibolite facies and isoclinally folded.

The formation is located within the Wilmington North, Kennett Square, West Grove, Newark West, and Newark East U. S. Geological Survey 7.5-minute quadrangles.

Seismometer:Teledyne Geotech S-13 Short period Vertical
Amplifier: Emtel 6243 Gain 24dB
VCO: 2380 Hz

Latitude: 39.72639
Longitude: -75.73611
Elevation: 90 meters above sea level

Elevation
90 meters above sea level
Latitude
39.73
Longitude
-75.74
Longitude2
-75.74
geolocation

39.72639, -75.73611

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Greenville (GEDE) Seismic Station

Greenville (GEDE) Seismic Station johncallahan Wed, 10/01/2014 - 11:46
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The seismic instruments located at the Greenville, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.

The equipment at this station was installed on 2013-04-28.

For more info, visit the station page at the Array Network Facility.

Instruments:

  • Quanterra Q330 Datalogger
  • Streckeisen STS-2 Broadband Seismometer
  • Setra 278 Microbarometer
  • NCPA Infrasound Microphone
  • MEMS Barometric Pressure Gauge

Latitude: 39.8113
Longitude: -75.6358
Elevation: 110 meters (NAVD88)

Elevation
110 meters (NAVD88)
Latitude
39.81
Longitude
-75.64
Longitude2
-75.64
geolocation

39.8113, -75.6358

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Milford (MIDE) Seismic Station

Milford (MIDE) Seismic Station johncallahan Wed, 10/01/2014 - 12:07
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The seismic instruments located at the Milford, DE location were adopted by DGS from the Earthscope Transportable Array, which consists of a network of 400 high-quality, portable broadband seismometers that are being placed in temporary sites across the United States. DGS adopted two of these Earthscope stations, P60A in Greenville, DE and Q61A in Milford, DE. This program provided an outstanding opportunity for Delaware to enhance its seismic monitoring capabilities in the future, and upgrade current antiquated equipment.

The equipment at this station was installed on 2013-05-28.

For more info, visit the station page at he Array Network Facility.

Instruments:

  • Quanterra Q330 Datalogger
  • Nanometrics Trillium 240 v2 Broadband Seismometer
  • Setra 278 Microbarometer
  • NCPA Infrasound Microphone
  • MEMS Barometric Pressure Gauge

Latitude: 38.8799
Longitude: -75.3256
Elevation: 10 meters (NAVD88)

Elevation
10 meters (NAVD88)
Latitude
38.88
Longitude
-75.33
Longitude2
-75.33
geolocation

38.8799, -75.3256

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Historical DGS Seismographs

Historical DGS Seismographs siteadmin Wed, 03/01/2017 - 11:22

Stream and Tide Gage Data for Hurricane Sandy

Stream and Tide Gage Data for Hurricane Sandy johncallahan Wed, 10/31/2012 - 15:41
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Introduction

Hurricane Sandy was a major storm event for the tidal areas of Delaware. As a part of the mission of the Delaware Geological Survey, we have compiled preliminary Delaware tide and stream-level data for Hurricane Sandy and compared them with previous flooding records. The following tables are the result of the compilation. Please note that these data are preliminary and are subject to change as the data are verified. We have also included some rainfall data to show the rainfall distribution throughout the state related to the storm. These data were provided by the Delaware State Climatologists Office (http://climate.udel.edu/) and were collected as part of the Delaware Environmental Operating System (DEOS, http://www.deos.udel.edu/). The following map shows the location of the stream and tide gages and the DEOS stations used in this report.

DEOS Station Storm Precipitation Total
Claymont, DE 5.21"
Newark (White Clay Creek) 6.05"
New Castle 5.73"
Glasgow 6.80"
Blackbird 8.39"
Dover 9.38"
Georgetown 7.92"
Laurel 8.22"
Rehoboth Beach 10.60"
Indian River Inlet 10.98"
Bethany Beach 7.83"
Rainfall data provided by DEOS.
 

Tidal Flooding

The following table is a summary of the preliminary tidal high water levels produced by Hurricane Sandy. The record high levels prior to Hurricane Sandy, the date of these levels, and the event (storm or hurricane) are shown for comparison. Nine record levels were reached for the tide gages on the Nanticoke River, in the Inland Bays and along the tidal portion of the Delaware River and its tributaries north of the Chesapeake and Delaware Canal. We have also included two NOAA tide gage graphs (at the bottom of this page) from Breakwater Harbor and Reedy Point that show the rise and fall of the tides during the storm. The difference between the predicted tides and the actual tides is the tidal surge that was the result of the storm.

  Hurricane Sandy Prior Record High    
Station Gage Height (ft) Date Timez Gage Height (ft) Date Event Tidal
Datum
Data
Source
Delaware River at Marcus Hook 9.94 10/30/12 3:30 9.76 4/17/11 low pressure system MLLW NOAA
Christina River at Newport ***8.06 10/30/12 2:18 8.07 9/17/99 Floyd NGVD 1929 USGS
Christina River at Wilmington 8.26 10/30/12 2:36 7.71 4/16/11 low pressure system NGVD 1929 USGS
Delaware River at New Castle failed during storm *7.68 5/12/08 Mothers Day Storm NAVD 1988 USGS
Delaware River- Delaware City 9.74 10/30/12 1:54 9.38 4/16/11 low pressure system MLLW NOAA
Reedy Pt.- Mouth of C&D Canal 9.10 10/30/12 1:42 9.23 4/16/11 low pressure system MLLW NOAA
Murderkill River at Frederica 4.84 10/29/12 13:18 5.15 5/12/08 Mothers Day Storm NGVD 1929 USGS
Murderkill River at Bowers 4.79 10/29/12 10:36 8.23y 3/3/94 Northeaster NAVD 1988 USGS
Ship John Shoal 9.42 10/30/12 0:12 9.29 4/16/11 low pressure system MLLW NOAA
Brandywine Shoal Light failed during storm 8.66 8/27/11 Irene MLLW NOAA
Breakwater Harbor at Lewes 8.70 10/29/12 9:36 9.22 3/6/62 March '62 Storm MLLW NOAA
Indian River Inlet **6.51 10/29/12 9:54 **5.86 2/5/98 Northeaster NGVD 1929 USGS
Indian River at Rosedale 6.23 10/29/12 10:48 6.99 2/5/98 Northeaster NGVD 1929 USGS
Rehoboth Bay at Dewey Beach 5.34 10/29/12 22:30 4.45 10/31/99 Halloween Northeaster NGVD 1929 USGS
Jefferson Creek at South Bethany 5.44 10/30/12 0:42 3.52 9/19/03 Isabel NGVD 1929 USGS
Little Assawoman Bay 4.82 10/30/12 0:00 3.13 10/25/05 Wilma NGVD 1929 USGS
Nanticoke River at Sharptown 5.59 10/30/12 4:36 4.11 3/3/94 Northeaster NGVD 1929 USGS
* gage malfunction, reading may be spurious
** data erratic, high winds and waves
*** no data collected between 2:18 and 4:18 EDT during peak tide
y previous tide gage, record for the present gage is 7.8 ft for the Mothers Day storm 5/12/08
9.94 red and bold indicates new record high
z Eastern Daylight Time

Stream Flooding

Although significant rainfall occurred throughout Delaware and in southeastern Pennsylvania, no new record stream levels were recorded. Flood stage was reached on five of the streams in northern Delaware. The levels shown in the following table are typical for a heavy rainfall event. We have also included three USGS hydrographs (at the bottom of this page) from the Brandywine at Wilmington, Red Clay Creek near Stanton, and White Clay Creek near Newark streamgages that show the rising water levels in the streams during the storm. It is possible or even likely that in areas in the Coastal Plain of Delaware where rainfall was the heaviest that small streams and ditches may have had significant flooding but no stream gages are located in these areas to record the event.

USGS Station Hurricane Sandy
Gage Height (ft)
Flood Stage (ft) Record
Gage Height (ft)
Event
Brandywine Crk at Wilm 16.66 16.50 *18.71 Hurricane Irene 2011
Shellpot Creek 5.78 8.00 13.76 Thunderstorm 1989
Red Clay Creek at Woodale >7.45** 7.50 17.62 TS Henri 2003
Red Clay Creek near Stanton 17.00 16.00 25.52 TS Henri 2003
White Clay Creek at Newark 9.84 11.50 17.13 Hurricane Floyd 1999
White Clay Creek near Newark 15.12 13.50 *17.57 Hurricane Floyd 1999
Christina River at Cooch's Bridge 12.35 10.50 13.73 Hurricane Floyd 1999
St. Jones River at Dover 7.70 - 11.72 Hurricane Irene 2011
Nanticoke River at Bridgeville 8.25 - 10.31 1979
* Record gage height at curent gage location
** Highest recorded value before going out of service during the storm

About the gages, stream and tide data

The Delaware Geological Survey (DGS) is actively involved in the monitoring of natural hazards such as stream and tidal flooding that are the result of large storms. The DGS identifies and investigates natural hazards to help understand the earth systems that present the hazards and determine strategies to prepare for or mitigate the risks. We are active in advising both county and state emergency management agencies on natural hazards. The DGS serves on the Delaware Emergency Management Agency’s (DEMA) Emergency Response Task Force for flooding, northeasters, and hurricanes and had staff located at the Delaware Emergency Operations Center during Hurricane Sandy.

An important component of monitoring storm events is having a real-time stream and tide gage network. These gages allow for monitoring of flooding during a storm as it happens to provide information to emergency managers and responders regarding areas of flooding and areas that may be flooded given the trends of rising stream or tide levels. The US Geological Survey, in cooperation with the Delaware Geological Survey, through a Federal-State partnership program operates and maintains stream and tide gages throughout Delaware.

Funding for operation and maintenance of this partnership program is provided by the Delaware Geological Survey, US Geological Survey, Delaware Department of Natural Resources and Environmental Control, Delaware Emergency Management Agency, City of Wilmington, City of Newark, and United Water Delaware.

The National Oceanic and Atmospheric Administration (NOAA) maintains tide gages in the Delaware Bay and River for purposes of navigation safety, environmental stewardship, and environmental assessment and prediction. These gages are an invaluable resource for real-time tidal conditions in the Delaware Bay and River.

Additional Information

Contact Us

For more information on Delaware flooding due to Hurricane Sandy, please contact Kelvin Ramsey at the Delaware Geological Survey (delgeosurvey@udel.edu, 302-831-2833.) For rainfall totals, please contact the Delaware State Climatologist Office.

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Fossils

Fossils johncallahan Fri, 06/25/2010 - 10:07

What is a fossil?

What is a fossil? johncallahan Mon, 07/13/2009 - 15:42
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The Glossary of Geology (Glossary of Geology, 4th edition, 1997, Edited by Julia A. Jackson: American Geological Institute, Alexandria, VA) defines a fossil as “any remains, trace, or imprint of a plant or animal that has been preserved in the earth’s crust since some past geologic or prehistoric time.” The field of geology involving the study of fossils is called paleontology. Fossils are of great use to geologists in understanding what the earth was like in the distant past and how life has changed through time. They are also a practical tool in the correlation of sedimentary rock layers from one area to another, which is an important part of exploring for petroleum and understanding the underground "plumbing" of groundwater systems.

Fossils can be fun to collect and interesting to study for the amateur, but they also tell geologists about the history of the world and how it was formed. The best time to look for fossils is after a heavy rain, when pieces of shell and fossil may be exposed in the soil. A stick is handy for scratching around in the top layer of soil. Collectors should remember their manners and should enter pits or other privately owned areas only after obtaining the owner's permission.

Delaware Geological Survey Special Publication Nos. 18 & 19 offer helpful hints for fossil identification and collection. These booklets are available by contacting the Survey or through the on-line ordering of DGS publications.

The most common fossils found in Delaware are from the Cretaceous period, and range from 65 to 100 million years in age. Some fossil collecting localities have also been found in central and southern Delaware, with the fossils generally being younger further south in the state. Fossils found in Kent County are commonly 12 to 20 million years old, and those in Sussex County mostly date from less than less than 1 million years.

Dinosaurs in Delaware?

Dinosaurs in Delaware? johncallahan Thu, 01/14/2010 - 21:45
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Only fragmentary remains of dinosaurs have been found in Delaware. All of these have come from the Chesapeake and Delaware Canal, mainly from the spoil piles created by the dredging of the Canal. Various nature groups in Delaware lead trips to the Canal for collecting. Most of the fossils found are those of marine invertebrates (primarily bivalves and gastropods with some remains of sponges, ammonites, and belemnites).

These fossils date to the late Cretaceous (97 to 65 million years ago) and come from the marine sediments of the Marshalltown and Merchantville Formations. Of the dinosaur remains, none have been complete enough for genus and species identification. At least two hadrosaurid (duck-bill dinosaurs such as Maiasaura) teeth have been found. Several toe bones of ornithomimosaur (small and agile theropod predators that look something like plucked ostriches with long tails and arms) dinosaurs and a partial hadrosaurid vertebra have been recovered. In addition to the dinosaur remains, other vertebrate fossils that have been recovered include: teeth of the marine reptiles Mosasaurus, Globidens, and Tylosaurus; part of a jaw and plates (scutes) of the giant crocodile Deinosuchus; a pleisiosaur vertebra; remains of bony fishes; and shell fragments of the turtles Trionyx, Toxochelys, and other forms. One of the most unique remains found in Delaware is that of a neck bone and a wing bone from a pterosaur (a flying reptile).

Sources of Information

There are many excellent books on dinosaurs available at your local library. A very good book on collecting dinosaur fossils in this region is one entitled "Dinosaurs of the East Coast" and was written by David B. Weishampel and Luther Young. It was published in 1996 by The Johns Hopkins University Press. The book is very thorough in describing dinosaur fossil collecting localities from all along the East Coast of North America, the kinds of dinosaurs to be found, and the habitats and lifestyles.

Another fine book on local dinosaurs is written by William B. Gallagher and is entitled "When Dinosaurs Roamed New Jersey." It was published by Rutgers University Press in 1997. It describes the dinosaur fossils that have been found in New Jersey as well as some information about those from Delaware. The information of dinosaurs from Delaware given above comes from these books. For information regarding the Cretaceous fossils from Delaware, the following are available from the Delaware Geological Survey:

Latitude
39.68
Longitude
-75.75
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Fossil Sites In Delaware

Fossil Sites In Delaware johncallahan Mon, 07/13/2009 - 15:47
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Delaware offers a few sites for fossil collectors, and the Chesapeake and Delaware Canal and the Pollack Farm are first two locations to check out. Much information is known about these two sites. More information is below, including references to DGS publications detailing the areas. Some other locations throughout the state also offer good hunting grounds for fossil collectors. If you know of good sites in Delaware not listed on this page, please feel free to contact us!

Chesapeake and Delaware Canal - Cretaceous Fossils

The Chesapeake and Delaware Canal is likely the best site in Delaware for fossil collecting. When the canal was built, several formations having fossils from the Cretaceous Period (144 to 65 million years ago) were exposed. Fossils found there represent life forms that existed for a good portion of that period of time and that lived in a shallow sea or along the seashore. The fossils include large clam and oyster shells and a pen-shaped fossil called a belemnite. The belemnite species Belemnitella americana is one of the more common fossils from this area and so was designated Delaware's state fossil. It comes from the inside of a squid-like animal that lived in the seas of the Cretaceous Period. Similar fossils are found in New Jersey and in England. Geologists can use this information to correlate geologic rock units in different areas, allowing them to link events in different parts of the world.

Most fossils found in the Canal area are called "steinkerns." These are formed when a shell fills with mud that later hardens. In some cases, the shell then dissolves, although at the Canal many original shells also are preserved. Other fossils commonly found at the Canal include fish and reptile bones, including vertebrae and teeth.

Good locations at the Canal to search for fossils are the dredge spoils near St. Georges and at the foundation of the Reedy Point Bridge. The U. S. Army Corps of Engineers has jurisdiction over the Canal lands, and small-scale collecting of fossils for private collections is permitted. It is against federal law to collect fossils from the area to sell.

For more information




Pollack Farm - Miocene Fossils

Located in Kent County, Delaware, the Pollack Farm Site was a surprise to many to contain numerous fossils. The fossils discovered range from a simple Arthropod, small insect, to large vertebrates, such as sharks. In 1991, while Delaware Geological Survey staff collected earth minerals during a highway construction, they came across an upper shell bed full of molluscan fossils. As digging continued numerous fossils of various species and phylum were found.

The Delaware Geological Survey provides a resource of facts and photos of the numerous fossils found in central Delaware. This site includes links to four main phylum, which lead to fossil photographs containing brief descriptions.

For more information




Delaware Mineralogical Society

The Delaware mineralogical Society is a nonprofit organization dedicated to the promotion and education of mineralogy, paleontology and the lapidary arts. They hold regular meetings, an annual rock and mineral show (with numerous fossils for sale, great for kids and collectors alike!), and field trips throughout the state and surrounding area. Refer to their website below for more information.




Other Fossil Sites in Delaware

Other locations throughout the state also offer good hunting grounds for fossil collectors. Just south of Dagsboro, where Route 113 crosses Pepper Creek, the collector can find young (less than 2 million year old) marine fossils from the Pleistocene Epoch. At the state sand and gravel pit just south of Middletown on Route 896, plant impressions from the Pleistocene may be found.

A variety of Miocene fossils are know from central Delaware. Fossils from the Miocene epoch, approximately 15 million years in age, have been found in the banks of the Coursey and Killen Ponds near Felton. This is addition to the fossils found at Pollack Farm.

For more information:

Fossil Identification Sheet

Fossil Identification Sheet johncallahan Thu, 04/15/2010 - 14:45
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Belemnite

In Delaware, the best place to look for Belemnitella americana is in the dredge spoil piles on the north side of the Chesapeake and Delaware Canal, just west of St. Georges and also just east of the north side of the Reedy Point Bridge. On July 2, 1996, belemnite was named as the official fossil of Delaware. More information can be found at Delaware's State Fossil.

Bivalve Steinkerns and Molds

A steinkern is an internal mold, or a type of fossil formed when a shell fills with mud that later hardens. The external molds of shells are also commonly fossilized. These molds were produced by shells of bivalves, the group of molluscs with two hinged shells such as clams, oysters, and scallops in Delaware's ancient seas. These bivalve steinkerns and molds are from the late part of the Cretaceous Period, approximately 65 to 85 million years old. These fossils were found along the Chesapeake and Delaware Canal.

Fossil Scallop

Along the western shore of the Chesapeake Bay in southern Maryland is a famous fossil collecting area known as the Calvert Cliffs. Among the many shells are beautiful fossil scallops, including forms like this called Pecten or Chesapecten. These fossils are from the Miocene epoch, between 5 and 25 million years old.

Gryphaea

Gryphaea is an oyster that lived in Delaware's shallow seas during the age of the dinosaurs. This fossil can be found along the Chesapeake and Delaware Canal, within the Mount Laurel Formation and the Marshalltown Formation, which were deposited between 65 and 85 million years ago during the late part of the Cretaceous Period.

Marine Mammal Bone

Along the western shore of the Chesapeake Bay in southern Maryland is a famous fossil collecting area known as the Calvert Cliffs. Among the shells are common bones and bone fragments which are the remains of ancient marine mammals (probably dolphins, whales and seals). Note the spongy appearance of the bone. These fossils are from the Miocene epoch, between 5 and 25 million years old.

Petrified Wood

Petrified wood may be found in pits and stream banks in northern Kent County and southern New Castle County, Delaware. This petrified wood occurs near where porous, sandy layers lie on layers that contain abundant fossil diatoms. Diatoms are microscopic shells made of silica, the same compound as opals. The silica is dissolved by water passing through the sand. When this water flows to and soaks the buried wood, it can recrystallize and fill the pores in the wood. The central Delaware petrified wood is from either the Miocene epoch (5 to 25 million years ago) or the Pleistocene epoch (10,000 years to 2 million years ago).

Cretaceous Fossils of the C&D Canal

Cretaceous Fossils of the C&D Canal johncallahan Fri, 06/25/2010 - 10:24

Cretaceous Fossils Overview

Cretaceous Fossils Overview johncallahan Mon, 07/13/2009 - 15:49
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The Cretaceous Period is the last period in the Mesozoic Era, a time in earth history commonly called "The Age of the Reptiles." This period lasted from approximately 144 to 65 million years ago.

Delaware was mostly an area of rivers, swamps, and dry land during the early part of the Cretaceous Period. During the late part of the Cretaceous, the sea covered most of Delaware. These ancient seas left deposits that contain the remains of marine life that lived on the sea bottom and swam in the water.

This web site is designed to show some of the fossil remains of this Cretaceous marine life that have been found in Delaware. Many fossils have been collected in the past from Cretaceous deposits exposed along the Chesapeake and Delaware (or C&D) Canal in northern Delaware. Most of the good collecting localities have been covered in recent years as the canal has been widened and improved, but in places fossils still can be found in "spoil piles," which are piles of material dug from the bottom of the canal when it is deepened or cleaned.

This web site describes many of the types of fossils that are known from the Cretaceous deposits of Delaware. It includes pictures and drawings of many of the fossils. It also provides a checklist of Delaware's Cretaceous as well as some maps that show collecting sites and the geology of the area.

Whether you are interested in collecting yourself, or just want to learn about Delaware's fossils, we hope this web page will give you helpful information.

One-celled Organisms: Phylum Protozoa

One-celled Organisms: Phylum Protozoa johncallahan Mon, 07/13/2009 - 15:54
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Protozoans are one-celled organisms that include the amoeba. One group of protozoans, the Foraminifera ("forams"), are among the most common fossils found in the Cretaceous of Delaware -- but are hard to study without a microscope. Forams build a hard outer covering -- some by secreting calcium carbonate or opaline silica, some by cementing sand grains -- in order to provide support and protection. The resulting many-chambered shells, which are commonly called "tests," are the parts preserved as fossils. Some are very simple, and others are very ornate.

Foraminifera live almost exclusively in marine environments. Some foraminifera live on the sea bottom or within sea bottom sediments -- these are referred to as benthic foraminifera. Others float in the water -- these are called planktonic. Certain species of benthic foraminifera are known to prefer to live in certain marine environments, making them useful in interpreting the marine conditions that existed in the past. Planktonic foraminifera are commonly useful for determining the age of ancient sediments because of the rapid evolution through time of many groups.

Forams are usually collected by special filtration and floatation techniques and studied under the microscope because of their tiny size. However, two genera from the Cretaceous of Delaware, Dentalina and Citharina, are large enough to be seen in a magnifying glass and are fairly common in the Mount Laurel dredge spoils.

Reference(s)

Photograph and figures from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Sponges: Phylum Porifera

Sponges: Phylum Porifera johncallahan Tue, 07/14/2009 - 01:07
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Phylum Porifera is a group of simple animals that includes the sponges. Porifera have no internal organs, nervous tissue, circulatory system, or digestive systems, making them the most primitive of the multi-cellular animals. To support and protect their soft bodies, sponges produce skeletons of calcium carbonate, silica, or a soft organic material called spongin. The most common fossil sponge in the Cretaceous sediments of Delaware is the genus Cliona. Cliona sponges lived on rocks and shells of the seafloor and commonly bored holes in these objects, in which it lived. To obtain food, the sponges filtered the water around them as it passed through tiny pores located on their outer walls. The sponge is common in the Mount Laurel Formation along the Canal.

Reference(s)

Photographs and figures from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Clams, Snails, and Squid: Phylum Mollusca, Class Gastropoda

Clams, Snails, and Squid: Phylum Mollusca, Class Gastropoda johncallahan Fri, 07/31/2009 - 10:08
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Gastropods is the group of molluscs that includes the snails. Many types secrete a single coiled or uncoiled shell for protection, and these shells may be found as fossils. Some species spend their lives crawling along the sea floor, eating algae or debris from rocks and bottom sediments. Others are predatory and feed on other molluscs such as clams and oysters by drilling with a "radula" or rasping tongue.

Most of the Cretaceous gastropod fossils from the Canal are internal casts (steinkerns). They are difficult to identify, and most can only be assigned to a family or genus. Gastropods are abundant in the spoils from the Mount Laurel Formation on both sides of the Canal in the vicinity of Reedy Point.

Photo Gallery
Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Clams, Snails, and Squid: Phylum Mollusca, Class Cephalopoda

Clams, Snails, and Squid: Phylum Mollusca, Class Cephalopoda johncallahan Fri, 07/31/2009 - 10:52
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Phylum Mollusca
Class Cephalopoda
Cephalopods are a group of molluscs that include the pearly chambered Nautilus, squids, and the octopus. They can be divided into three categories: the Nautiloidea (chambered Nautilus), the Ammonoidea (the extinct ammonites), and the Dibranchiata (squids, the extinct belemnites, and octopuses).

Ammonite fossils occur in places in the Cretaceous of Delaware. An ammonite can be thought of as an octopus stuffed inside a straight, coiled, or spiral shell. They are uncommon finds at the C & D Canal, usually occuring as broken pieces; a complete one is a rare and exciting find. Most of the larger coiled ones are found in the Merchantville Formation. Sections of the straight-shelled Baculites are more common in the Mount Laurel Formation.

The belemnite species Belemnitella americana is the Delaware State Fossil. They are amber colored, bullet-shaped fossils that served as the internal skeleton in an extinct squid-like animal called a belemnoid. Belemnites are a common find on the Mount Laurel spoils pile because they probably traveled in large schools.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Clams, Snails, and Squid: Phylum Mollusca, Class Pelecypoda

Clams, Snails, and Squid: Phylum Mollusca, Class Pelecypoda johncallahan Fri, 07/31/2009 - 10:36
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Phylum Mollusca
Class Pelecypoda
Pelecypods have two shells, or bivalves, that protect the soft parts of the animal. The valves are generally of equal size (except in groups like the oysters) and shape and are hinged at the back. Some types, such as oysters, live in large groups that create beds or low-relief banks of shells, where the animals feed by filtering plankton and organic debris from the water. Other bivalves burrow through the mud or swim about in search of debris to eat. Many bivalve fossils in Delaware are preserved as steinkerns. Pelecypods are abundant in the spoils from the Mount Laurel Formation on both sides of the Canal in the vicinity of Reedy Point.

Photo Gallery
Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Corals and Jellyfish: Phylum Cnidaria

Corals and Jellyfish: Phylum Cnidaria johncallahan Tue, 07/14/2009 - 12:37
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Cnidarians are soft-bodied animals that include corals, jellyfish, and sea anemones. These soft-bodied animals have saclike digestive cavities and tentacles containing rows or stinging cells used for defense and capture of food. Many secrete calcium carbonate to support and partly enclose the soft parts; the most familiar of these are corals. The only members of the phylum found at the Canal are solitary corals. One of these corals, Micrabacia, may be the most common fossil found. Another common fossil found there, a solitary horn-shaped coral, has been given different names by different authors.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Insects and Crustaceans: Phylum Arthropoda

Insects and Crustaceans: Phylum Arthropoda johncallahan Fri, 07/31/2009 - 11:08
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Phylum Arthropoda
Arthropods are animals with a segmented body, external skeleton, and jointed appendages. The Arthropoda includes insects and crustaceans. Only two groups of arthropods are common as fossils in the Cretaceous of the C&D Canal area, and both are types of crustaceans: the Malacostraca (crabs, lobsters, and shrimp) and the microscopic Ostracoda.

The most common crustacean fossils come from the ghost shrimp Callianassa. Pieces of the claws and pinchers are the most common body parts found; only around the area of the Deep Cut have complete appendages been found. More common than body parts are the burrows of this shrimp, which occur as lumpy tubes called called Ophiomorpha nodosa. These "trace fossils" are very common in the Englishtown and Marshalltown formations.

Occasionally, small crabs (Tetracarcinus subquadratus) or fragments of lobsters (Hoploparia gabbi) are found on some of the spoil areas from the Merchantville and Marshalltown Formations.

Ostracodes can be collected by studying the sand-sized residue from screenings of the Mount Laurel Formation.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Lamp Shells: Phylum Brachiopoda

Lamp Shells: Phylum Brachiopoda johncallahan Mon, 07/20/2009 - 14:43
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Brachiopods are shelled invertebrate that look somewhat like bivalved molluscs. However, the animal living in the shell is a filter feeder that collects food with a special organ called a lophopore (bryzozoa also have lophophores).

Like clams, the brachiopod lives in a shell consisting of two hinged valves, but the orientation of the shells is different. Brachiopods have valves covering the top and bottoms of the animal that are of different sizes and shapes, but the left and right sides are are symmetrical (or mirror images to each other). In contrast, the valves of a clam shell are mirror images of each other, but the individual valves are asymmetrically shaped.

Brachiopods spend their adult life as bottom dwelling filter-feeders. They have generally decreased in abundance and diversity since the Paleozoic Era. Some types are fairly common, easy to identify, and are restricted to certain periods of time. These features make them important index or guide fossils. The brachiopod species Terebratulina cooperi is an index fossil for the Mount Laurel Formation in Delaware.

Reference(s)

Photographs from DGS Special Publication No. 18, 1988, by E. M. Lauginiger; DGS Special Publication No. 19, 1992, compiled by T.E. Picket and D.C. Windish; and DGS Report of Investigation No. 21, 1972, by T. E. Pickett.

Moss Animals: Phylum Bryozoa

Moss Animals: Phylum Bryozoa johncallahan Mon, 07/20/2009 - 14:38
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Bryozoans, sometimes referred to as "moss animals," are a type of simple colonial animal that mostly lives in marine environments (a few inhabit freshwater). Bryozoans feed by means of a lophophore, a small ring of tentacles covered with tiny cilia that are used to filter food from the water. Bryozoan colonies are protected with a covering of organic materials or calcium carbonate. Some calcium carbonate forms may be found as fossils in the Cretaceous strata near the C & D Canal.

Three species of bryozoans have been found in the spoils piles (refuse material from excavation of the canal) in the area of Reedy Point. The origin of these bryozoans is under much debate. Their occurrences are most commonly reported from the Mt. Laurel Formation. However, an alternative view is that many are from sediments of the overlying, Tertiary-age Vincentown Formation, which is exposed to the south - if so, they would have been washed into the eastern end of the Canal by the Delaware River and then dumped on the spoils with the other dredgings.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Segmented Worms: Phylum Annelida

Segmented Worms: Phylum Annelida johncallahan Fri, 07/31/2009 - 11:01
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Phylum Annelida
Annelids are segmented worms. The remains of the soft-bodied segmented worms are not usually preserved as fossils. Some marine (salt-water) types, however, secrete tubes of calcium carbonate to use both as a home and to provide protection from their enemies. These tubes can be found as isolated specimens or attached to larger shells. Two genera, Serpula and Hamulus, are fairly common in formations near the C&D canal.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Starfish and Urchins: Phylum Echinodermata

Starfish and Urchins: Phylum Echinodermata johncallahan Fri, 07/31/2009 - 12:53
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Phylum Echinodermata
Echinoderms are "spiny-skinned" invertebrate animals that live only in marine environments. Two major divisions are recognized by biologists: principally attached, usually stalked forms of the Pelmatozoa; and unattached free-moving forms of the Eleutherozoa.

Fossil Pelmatozoa are represented in Delaware by stem fragments or columnals from crinoids or sea lilies. Columnals belonging to the Cretaceous crinoid Dunnicrinus are common finds on the Reedy Point spoils. The calyx or head of this crinoid has not been found, probably because of its fragile nature.

Eleutherozoan fossils include a group of starfish-like, free-moving forms called brittle stars, and a group of armless spiny forms known as sea urchins. Complete sea urchins are rare and highly prized specimens. The most common finds along the canal are isolated spines and plates of sea urchins and small fragments of brittle stars.

Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Vertebrates: Phylum Chordata

Vertebrates: Phylum Chordata johncallahan Fri, 07/31/2009 - 13:06
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Phylum Chordata includes the vertebrates. Although not as common as the invertebrates, teeth and bones from different classes of vertebrate animals can be found at Canal sites.

Chondrichthyes, or “cartilage fish,” include the sharks, skates, and rays. Teeth and vertebrae from these animals are the most common types of vertebrate fossil found. They may be found on the surface of a rock outcrop or in various spoil piles.

The most commonly found shark teeth belong to the extinct shark Squalicorax. These broad and serrated teeth are easy to identify to the genus level, but it is more difficult to distinguish between the species. Teeth of the goblin shark, Scapanorhynchus, are the largest shark teeth found at the Canal, with some specimens reaching over two inches in length. The teeth of this shark have caused workers much confusion because teeth from different parts of the mouth have different and distinct shapes. At one time there were three different names given to the teeth of this single shark species.

Osteichthyes, or “bony fish,” are represented by the dagger-like teeth of the Cretaceous predator Enchodus. Single, isolated teeth and small sections of the jaw with teeth still attached are relatively common finds. Teeth from other bony fish include Anomoeodus and Stephanodus. Vertebral columns of bony as well as cartilaginous fish are also found on the spoil piles.

Reptile remains are rare and thus the most treasured finds from the Delaware Cretaceous. Teeth of the sea-going reptile Mosasaurus and fragments from the upper and lover shells of turtles are the usual finds. Most collectors have to hunt for years before they find a single mosasaur tooth.

Photo Gallery
Reference(s)

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Miocene Fossils of Pollack Farm

Miocene Fossils of Pollack Farm johncallahan Fri, 06/25/2010 - 10:24

Miocene Fossils Overview

Miocene Fossils Overview johncallahan Tue, 07/14/2009 - 13:03
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The Pollack Farm Site, located in Kent County, Delaware, is named for a borrow pit on the former Pollack property that was excavated during 1991 and 1992 for road material used in the construction of Delaware State Route 1. While Delaware Geological Survey staff collected earth minerals during construction of State Route 1, they came across an upper shell bed full of molluscan fossils. As digging continued, numerous fossils of various species and phylum were found. The fossils discovered range from a simple Arthropod, small insect, to large vertebrates, such as sharks. By 1993, the pit was back-filled, graded, and developed into a wetlands mitigation site.

The Delaware Geological Survey has created this web page to provide a resource of facts and photos of the numerous fossils found in central Delaware. The site includes links to four main phylum, which lead to fossil photographs containing brief descriptions.

In designing this website we hope to provide you with information that will be both educational and enjoyable!

Latitude
39.24
Longitude
-75.58
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Bivalves: Phylum Mollusca, Class Bivalvia

Bivalves: Phylum Mollusca, Class Bivalvia johncallahan Tue, 07/14/2009 - 14:06
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Clams, mussels, oysters, and scallops are members to the class Bivalvia (or Pelecypodia). Bivalves have two shells, connected by a flexible ligament, which encase and shield the soft vulnerable parts of the creature. All 15,000 known species of bivalves are aquatic in nature, with close to 80% being marine (saltwater environments).

Living at the bottom of the marine environment bivalves tend to either swim using their mantle cavity to force water movement, burrow into the sand, or attach themselves to an object with sticky strings called "byssal threads."

Below is a list of notable Bivalve species found at the Pollack Farm site.

  • Dallarca sp.
  • Astarte distans
  • Astarte sp.
  • Cyclocardia castrana
  • Glossus sp.
  • Iphigenia sp.
  • Caryocorbula subcontracta

Click the image or the link below to view the bivalvia collection!

Latitude
39.24
Longitude
-75.58
Reference(s)

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/File:Cockle.jpg

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Snails and Slugs: Phylum Mollusca, Class Gastropoda

Snails and Slugs: Phylum Mollusca, Class Gastropoda johncallahan Tue, 07/14/2009 - 13:51
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The Class Gastropoda (in Phylum Mollusca) includes the groups pertaining to snails and slugs. The majority of gastropods have a single, usually spirally, coiled shell into which the body can be withdrawn. The shell of these creatures is often what is recovered in a fossil dig. Gastropods are by far the largest class of molluscs, comprising over 80% of all molluscs.

The presence of gastropods, at the Pollack site, provides evidence to validate the researchers beliefs that, years ago, the environment was of shallow-water, near-shore locality.

Below are a few notable taxa recovered from the Pollack Farm site.

  • Gastrapoda:
  • Turritella cumberlandia
  • Diastoma insulaemaris
  • Epitonium charlestonensis
  • Urosalpinx cumberlandianus
  • Tritonopsis ecclesiastica
  • Nassarius sopora
  • Oliva simonsoni
  • Inodrillia whitfieldi

Click the image or the link below to view the gastropod collection!

Latitude
39.24
Longitude
-75.58
Reference(s)

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/ File:Orange_slug.jpg

Birds: Phylum Chordata

Birds: Phylum Chordata johncallahan Fri, 07/31/2009 - 13:58
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The lower Miocene Pollack Farm Fossil Site has yielded few avian fossils in comparison to the other classes of vertebrates and invertebrates. Only eleven fossil fragments, assignable to six taxa, were collected at the Pollack site. Of the eleven avian fossils collected, representations from three distinctive orders were recovered: Gaviiformes (divers and loons, seen below), Charadriiformes (gulls and shore birds), Pelecaniformes (cormorants and pelicans).

Fossil fragments such as the proximal end of right scapula(order Charadriiformes), Middle trochlea of left tarsometatarsus (order Pelecaniformes) are some of the few materials paleontologist were able to gather.

Other taxa represented include:

Gavia small sp. (1 specimen and possibly another) Morus cf. M. loxostylus (5 specimens)
large species of pseudodontorn (1 specimen)

Although the number of remains is relatively small to other phylum and classes collected, the groups importance can not be undermined due to the information they provide in explaining the past environment of the lower Miocene bed. Because the majority of the birds represent groups that are largely or entirely marine, it further strengthens the hypothesis that the lower Miocene formation was once a near shore area of an embayment.

Click the image or the link below to view the avian fossil collection.

Latitude
39.68
Longitude
-75.75
Reference(s)

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/File:TringaSemipalmata_3897.JPG

Fish: Phlyum Chordata

Fish: Phlyum Chordata johncallahan Mon, 07/20/2009 - 12:34
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While sampling the lower Miocene Calvert Formation at the Pollack Farm Site, 30 fossil fish taxa were collected, consisting of 24 cartilaginous and 6 osteichthyes fishes. The fossils found in the lower Miocene bed have similar characteristics to an equally aged Formation in southern Delaware suggesting deposition occured in a subtropical, shallow-water, near shore environment.

The early Miocene Fish fossils found in Delaware are of two kinds, Chondrichthyes(consisting mainly of Sharks and rays) and Osteichthyes(commonly known as bony fish).

Paleontologists, at the Pollack Farm, were able to collect a large number of teeth and vertebrae from Chondrichthyes. However, because their bodies do not contain a true bone, full body fossils are very rare to find.

Osteichthyes, differ than Chondrichthyes, in that their skeleton is made of a stiffer bone, compared to their cartilaginous counterparts. Osteichthyes are often associated with dagger-like, isolated teeth

The stingray, dayatis americana, (shown above) is just one of the many Chondrichthyes and fish fauna found at the Pollack Farm Site, in Delaware! Click the image or the link below to view the fish collection.

Latitude
39.24
Longitude
-75.58
Reference(s)

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.pbs.org/oceanrealm/seadwellers

Insects and Crustaceans: Phylum Arthropoda

Insects and Crustaceans: Phylum Arthropoda johncallahan Mon, 07/20/2009 - 12:19
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The majority of Arthropods recovered at the lower Miocene bed are from various species of crustaceans (lobsters, shrimp, barnacles). Fossils from crustaceans often consist of small body parts such as claws. However, crustaceans such as ghost shrimp (callichirus) tend to construct burrows that resemble lumpy tubes called Ophiomorpha. These corn-stalked resembling tunnels, are created from mud and depository waste to form burrows in which the creatures reside. In comparison to claws and pincher fossils, "trace fossils", such as Ophiomorpha tubes, are often commonly found in greater number than that of various body parts.

Arthropods include an exceedingly diverse group of taxa such as insects, crustaceans, spiders, scorpions, and centipedes. There are more species of arthropods than species in all other phyla combined. The name Arthropod means "jointed foot." All arthropods have segmented bodies and are enclosed in a jointed, protective armor called an exoskeleton. Most arthropods have a pair of compound eyes and one to several simple ("median") eyes or ocelli.

In addition to shrimp and other shellfish, barnacles are commonly found in the lower Miocene bed. Barnacles are separated into two groups sessil and stalked. Both have soft bodies that are protected by an outer wall, which resembles either an acorn (sessil) or stalk. Living in a tight grouping with other barnacles these creatures attach themselves to any suitable surface (rocks, boats, even whales and turtles!) in effort to aid in reproduction.

The trace fossils for Arhtropods found at the Pollock Site include Ophiomorpha nodosa (burrow tubes dug by shrimp) and Skolithos linearis (burrow tubes left by ground-dwelling insects).

Click the image or the link below to view the Arthropod collection.

Latitude
39.24
Longitude
-75.58
Reference(s)

Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.pbs.org/kcet/shapeoflife/animals/arthropods4.html

Land Mammals: Phylum Chordata

Land Mammals: Phylum Chordata johncallahan Fri, 07/31/2009 - 14:18
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Land mammal fossils were discovered in 1992 in the lower part of the Calvert formation at the Pollack Farm site. During the short time the pit was open, the collection grew to become the most diverse tertiary land mammal fauna known north of Florida on the eastern half of North America.

The gathering, collected from the lower Miocene formation, includes at least 26 species representing at least 17 families in 7 orders (listed below).

Orders:

  • Soricomorpha (Shrews, moles)
  • Erinaceomorpha (Hedge hogs)
  • Chiroptera (Bats)
  • Rodentia (Rats, mice)
  • Carnivora (Bears, wolves)
  • Perissodactyla (Rhinoceros, horses)
  • Artiodactyla (Deer)

The Collection of Miocene land mammal fossils, especially north of Florida, is relatively minimal. Only four localities distancing between Georgia and New Jersey yielded significant Miocene fossil beds. Although single teeth and parts of postcranial elements represent the majority of land mammals of the Pollack Farm local fauna, the sites diversity of species elevates the importance of the Pollack Farms location.

Click the image or the link below to view the Land Mammal collection!

Latitude
39.68
Longitude
-75.75