Assawoman Bay Group

Geologic Time Period
middle to late Pleistocene

Coastal Plain - Primarily Surficial Unit

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).


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.