Abstract: Preliminary Calcareous Nannofossil Zonation of Brightseat and Aquia Formations (Paleocene) of Maryland and Virginia--Stratigraphic Implications
Laurel M. Bybell, David L. Govoni
Fossiliferous glauconitic quartz sand and silt of the basal Tertiary Brightseat Formation and the overlying Aquia Formation are exposed in the Potomac and Severn River valleys in an irregular northeast-trending belt extending from Stafford County, Virginia, southwest of Washington, D.C., into Anne Arundel County, Maryland, northwest of Annapolis. Lithostratigraphic analysis of these formations at selected outcrops provides a physical stratigraphic framework for a preliminary local biostratigraphic zonation based upon calcareous nannofossils.
The microflora and lithology of the stratigraphic interval examined indicate two significant disconformities. The current study indicates that the first of these disconformities, at the Brightseat-Aquia contact, may encompass as much as the upper half of the Danian, a maximum time interval of about 3.5 m.y. Although our calculation of its magnitude agrees with earlier work, this disconformity previously has been thought to represent a somewhat younger age (late Danian to early Landenian). The second disconformity, within the Aquia Formation in the upper part of the Piscataway Member, may represent an entire nannofossil zone and be equivalent to approximately 0.5 m.y., a time period of significantly greater duration than normally would be suspected on the basis of lithologic evidence a one.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC