Stratigraphy of Yorktown (Lower and Middle Pliocene) and Chowan River (Upper Pliocene) Formations in Southeastern Virginia: ABSTRACT

Abstract

The Yorktown and Chowan River formations exhibit vertical and lateral variations in lithology and fauna. The Yorktown, which rests disconformably on the Eastover Formation (upper Miocene), is comprised of a fossiliferous shallow marine sand with a discontinuous basal pebbly sand (Sunken Meadow Member). The upper Yorktown consists of intertonguing and intergrading shelf, shoal, and restricted marine deposits (Rushmere, Mogarts Beach, Moore House, and a possible unnamed uppermost member). The shelf deposits are principally fossiliferous, marine silty fine sand, and the shoal sediments are planar and cross-bedded biofragmental sands. The restricted marine sediments range from silty fine sand to silty clay and contain a limited fauna. Near the Fall Zone, the Yorktown is compr sed of nonfossiliferous quartz-rich sand. Differential upward movement of the outer Atlantic coastal plain created an offshore shoal, west of which were embayed conditions. The Bacons Castle, Windsor, and higher formations rest with a regional angular unconformity on the Yorktown. The Chowan River formation is restricted to the outermost coastal plain in Virginia and is composed of planar and cross-bedded shelly fine sand. The basal Chowan River contains scattered allochthonous pebbles and boulders, sideritic nodules, and brackish to marine fossil assemblages. The Yorktown and Chowan River formations represent the last incursions of relatively warm seas into southeastern Virginia during the late Tertiary. End_of_Article - Last_Page 1438------------