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.
The following table displays the correlation of hydrologic units to geologic units recognized by the Delaware Geological Survey in the Atlantic Coastal Plain.
The stratigraphy of the Coastal Plain of Delaware is discussed with emphasis placed upon an appraisal of the stratigraphic nomenclature. A revised stratigraphic column for Delaware is proposed. Rock stratigraphic units, based mainly on data from certain key wells, are described and the published names which have been or which might conceivably be applied to those units are reviewed. In each case a name is chosen and the reasons for the choice are stated. The relationships between the column established for Delaware and the recognized columns for adjacent states are considered.
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.
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.
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.
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.
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.
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.
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.