Calvert Formation

Birds: Phylum Chordata

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).

Reptiles: Phlyum Chordata

The Pollack Farm Site has provided the first legitimate window of Miocene reptilian life in North America east of the great plains and north of Florida. In years prior to the excavation of the Pollack site, records of particular small lizards and snakes were non-existent in locations of the mid-Atlantic and northeast, thus providing a significant value to the Miocene fossils recovered.

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.

RI55 Geology of the Milford and Mispillion River Quadrangles

Investigation of the Neogene and Quaternary geology of the Milford and Mispillion River quadrangles has identified six formations: the Calvert, Choptank, and St. Marys formations of the Chesapeake Group, the Columbia Formation, and the Lynch Heights and Scotts Comers formations of the Delaware Bay Group. Stream, swamp, marsh, shoreline, and estuarine and bay deposits of Holocene age are also recognized. The Calvert, Choptank, and St. Marys formations were deposited in inner shelf marine environments during the early to late Miocene.

Calvert Formation

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.

RI50 Plant Microfossils of the Calvert Formation of Delaware

The Calvert Formation, deposited in a shallow sea during the late Oligocene and early to middle Miocene (15-27 million years ago), contains a very rich fossil microflora, both in terms of number of specimens and number of species. Most abundant are pollen of oak, pine, and hickory, but exotic taxa (those that no longer occur in Delaware) are present in all samples of this formation. They include pollen of Engelhardia type, Manilkara, Planera (water elm), Alangium(?), and palms.

Fish: Phlyum Chordata

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.

Insects and Crustaceans: Phylum Arthropoda

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.