The Geology of Delaware

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Ironshire Formation

Geologic Time Period: 
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 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.


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.