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| Nanjemoy Formation | |
|---|---|
| Stratigraphic range: Ypresian (Wasatchian) ~ | |
| Type | Formation |
| Unit of | Pamunkey Group |
| Sub-units | Woodstock & Potapaco |
| Underlies | Piney Point & Calvert |
| Overlies | Aquia & Marlboro Clay |
| Thickness | About 20 m (66 ft) |
| Lithology | |
| Primary | Sandstone, claystone |
| Other | Marl, limestone |
| Location | |
| Coordinates | 38°48′N 76°42′W / 38.8°N 76.7°W |
| Approximate paleocoordinates | 39°06′N 60°48′W / 39.1°N 60.8°W |
| Region |  Virginia Maryland District of Columbia |
| Country |  United States |
| Extent | Extent |
| Type section | |
| Named for | Nanjemoy Creek Etymology |
| Named by | Clark & Martin |
| Year defined | 1901 |
  Nanjemoy Formation (the United States)  Nanjemoy Formation (Maryland) | |
The Nanjemoy Formation is a geologic formation pertaining to both the Wilcox Group and the Pamunkey Group of the eastern United States, stretching across the states of Virginia, Maryland, and District of Columbia. The formation crops out east of the Appalachians and dates back to the Paleogene period. Specifically to the Ypresian stage of the Eocene epoch, about 55 to 50 Ma or Wasatchian in the NALMA classification, defined by the contemporaneous Wasatch Formation of the Pacific US coast.
The about 20 metres (66 ft) thin formation crops out in a narrow irregular band and only in certain of the many creeks of the Maryland peninsula and on the southern side of the Potomac River in Virginia. The two members the formation was divided into by Clark and Martin in 1901; Potapaco and Woodstock, represent different phases in the basin history. The lower Potapaco Member is much more clayey, described as marl, than the upper Woodstock Member, probably characteristic of less storm influences in the shallow shelf sediments.
The formation has provided a wealth of fossils of mainly fish, but also mammals, reptiles, birds and flora. The presence of the sharks Otodus obliquus and Carcharocles aksuaticus, as well as various other shark and ray species are notable. Crocodylian, snake, turtle, mammal, and bird remains have all been found in the Nanjemoy Formation.[1]
- ^ Weems & Grimsley, 1999