Nanjemoy Formation
| 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 the District of Columbia. The formation crops out east of the Appalachians and dates back to the Ypresian stage of the Eocene epoch, about 55 to 50 Ma or Wasatchian in the NALMA classification. It is roughly contemporaneous with the Wasatch Formation of the Interior West.
The 20 metres (66 ft)-thick formation crops out in a narrow irregular band in some of the creeks in southern Maryland, and on the southern side of the Potomac River in northern Virginia. The formation was divided into two members by Clark and Martin in 1901; the Potapaco and Woodstock, representing different phases in the basin history. The lower Potapaco Member is much more clayey, described as marl, than the upper Woodstock Member, which is 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 Otodus 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.