The Geology of Delaware

Share

First State Geology Newsletter Signup

First State Geology has been the newsletter of DGS for over 25 years.

Click here to signup!

Beaverdam Formation

Tbd
Geologic Time Period: 
upper Pliocene
Coastal Plain - Primarily Surficial Unit

The following description was published in GM15 Geologic Map of the Georgetown Quadrangle, Delaware, Ramsey, K.W., 2010:

Heterogeneous unit ranging from very coarse sand with pebbles to silty clay. Predominant lithologies at land surface are white to mottled light-gray and reddish-brown, silty to clayey, fine to coarse sand. Laminae and beds of very coarse sand with pebbles to gravel are common. Laminae and beds of bluish-gray to light-gray silty clay are also common. In a few places near land surface, but more commonly in the subsurface, beds ranging from 2- to 20-ft thick of finely laminated, very fine sand and silty clay are present. The sands of the Beaverdam Formation commonly have a white silt matrix that gives drill cuttings a milky appearance (Ramsey, 2001, 2007). This white silt matrix is the most distinguishing characteristic of the unit and readily differentiates the Beaverdam Formation from the adjacent clean sands of the Turtle Branch Formation. Interpreted to be a fluvial to estuarine deposit of late Pliocene age on the basis of pollen assemblages and regional stratigraphic relationships (Andres and Ramsey, 1995a, 1996; Groot and Jordan, 1999; Groot et al., 1990). Ranges from 50 to 120 ft thick in the Georgetown Quadrangle.

The following description was published in GM14 Geologic Map of Kent County, Delaware, Ramsey, K.W., 2007:

Light gray to white coarse to very coarse sand with beds of fine to medium sand. Sands are quartzose, moderately feldspathic (< 20% feldspar), and often have a white silt to clayey silt matrix giving drill cuttings a milky appearance. Beds of sandy silt, clayey-sandy silt, and clayey silt are common. Beds of dark gray to brown pollen-bearing organic-rich clayey silt are rare to common (Andres and Ramsey, 1995a, 1995b). Beds of light yellow-orange medium to coarse sand, gravelly sand, sandy gravel, and dark gray or blue- to green-gray clayey silt are also rare to common. Basal beds are gravelly with pebbles of quartz and quartzite with lesser amounts of chert, sandstone, and a variety of lithic clasts. Thickness up to 75 to 100 feet in southernmost portion of the county. Interpreted to be a Pliocene fluvial to estuarine deposit (Andres and Ramsey, 1996; Groot and Jordan, 1999).