upper Miocene

RI75 Stratigraphy and Correlation of the Oligocene to Pleistocene Section at Bethany Beach, Delaware

The Bethany Beach borehole (Qj32-27) provides a nearly continuous record of the Oligocene to Pleistocene formations of eastern Sussex County, Delaware. This 1470-ft-deep, continuously cored hole penetrated Oligocene, Miocene, and Pleistocene stratigraphic units that contain important water-bearing intervals. The resulting detailed data on lithology, ages, and environments make this site an important reference section for the subsurface geology of the region.

Choptank Formation

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 units. 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.

St. Marys Formation

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).

RI47 Ages of the Bethany, Beaverdam, and Omar Formations of Southern Delaware

The microflora of the Bethany formation and the lower part of the Beaverdam Formation is characterized by a Quercus-Carya assemblage, very few non-arboreal pollen, and Pterocarya and Sciadopitys as exotic constituents. This assemblage has much in common with that of the Brandywine Formation of Maryland and the Eastover Formation of Virginia which are of late Miocene or early Pliocene age. The environment of deposition of the Bethany was probably deltaic, and that of the lower Beaverdam fluviatile.

Fossil Sites In Delaware

Delaware offers a few sites for fossil collectors, and the Chesapeake and Delaware Canal and the Pollack Farm are the best. 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.

What is a fossil?

If you think you may have found a Delaware dinosaur or any unusual fossil, the scientists at the Delaware Geological Survey at the University of Delaware, Newark campus would like to see it. It could provide important information on the geologic history of the First State.

B20 Stratigraphy of the Post-Potomac Cretaceous-Tertiary Rocks of Central Delaware

This Bulletin presents the subsurface stratigraphy of the post-Potomac Cretaceous and Tertiary rocks of the Atlantic Coastal Plain of central Delaware, between the Chesapeake and Delaware (C & D) Canal and Dover. Geophysical log correlations supported by biostratigraphic and lithologic data from boreholes in Delaware and nearby New Jersey provide the basis for the report.

B18 Clay and Clay-Size Mineral Composition of the Cretaceous-Tertiary Section, Test Well Je32-04, Central Delaware

This study complements Delaware Geological Survey Bulletin No. 17 and deals exclusively with clays and clay-size minerals. The cored section at the location of Je32-04 has been subdivided into 25 clay zones on the basis of major changes in trends and degree of crystallinity of clay minerals. The composition of clay minerals varies from zone to zone. These clay minerals have been identified: kaolinite, berthierine, chlorite, illite, smectite, chlorite/smectite, illite/smectite, glauconite/smectite, and glauconite pellets.

B17 Geological Studies of Cretaceous and Tertiary Section, Test Well Je32-04, Central Delaware

A cored well 1,422 feet (433 meters) deep drilled two miles southeast of Dover is the basis for this integrated study of the lithology and paleontology of the Cretaceous-Tertiary section in central Delaware. The section is subdivided into lithostratigraphic, biostratigraphic, chronostratigraphic, and heavy mineral units. Data and results are presented on a common base in three plates.

B13 Geology, Hydrology, and Geophysics of Columbia Sediments in the Middletown-Odessa Area, Delaware

Columbia sediments in the Middletown-Odessa area are composed of boulders, gravels, sands, silts and clays. These sediments are exposed in four gravel pits where their structures and textures were studied. Subsurface geology was interpreted on the basis of the well-log data from 40 holes drilled in the area of study. Columbia sediments were laid upon a surface made up of the greensands of the Rancocas Formation (Paleocene – Eocene age). The contact between the Rancocas and Columbia Formations is an erosional unconformity.