Abstract: Mesozoic and Cenozoic Biostratigraphy of Oak Grove Core, Northeastern Virginia

G. W. Andrews, L. M. Bybell, R. A. Christopher

Calcareous nannofossils, diatoms, dinoflagellates, foraminifers, mollusks, ostracods, and sporomorphs from a 412-m core hole near Oak Grove, Westmoreland County, Virginia, have been studied.

The uppermost 20.5 m consists of upland gravels of probable Pliocene and Pleistocene age and was not cored.

Underlying the uppermost 20.5 m is 39.5 m of fine-clastic deposits of the Calvert Formation of early and middle Miocene age. Calcareous fossils are absent, but diatoms and dinoflagellates suggest that a nearly complete section of the Calvert is represented. Deposition was in shallow, open-marine waters.

From 60 to 96 m are micaceous glauconitic sands of the Nanjemoy Formation, representing early and middle Eocene age (Sabinian and Claibornian). Deposition was in shallow, open-marine waters. The Marlboro Clay Member, 5.5 m thick, is at the base of the formation. The upper gray part of the member contains a sparse microfauna suggesting an early Eocene age; the lower red clays are devoid of fossils.

Below the Marlboro to a depth of 127.5 m are glauconitic sands of the Aquia Formation. These shallow-marine deposits are of late Paleocene age. From 127.5 to 138.4 m are clayey sands containing dinoflagellates suggestive of an early Paleocene (Danian) age, probably representing a southern extension of the Brightseat Formation.

The section from 138.4 m to the bottom at 412 m is assigned to the Potomac Group and consists of clastic deposits of Early Cretaceous age and nonmarine origin. Two polleniferous intervals were found, from 182 m to 238 m and from 274 m to the bottom of the core. The upper interval is indicative of pollen zone IIB of a possible middle Albian age; the lower interval is assigned to zone I, of Barremian or Aptian age.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC