LATE CENOZOIC LANDFORMS, STRATIGRAPHY AND HISTORY OF SEA LEVEL OSCILLATIONS OF SOUTHEASTERN VIRGINIA AND NORTHEASTERN NORTH CAROLINA.

摘要

A depositional model accounting for the stratigraphic sequences which accumulate during a marine transgression across a dissected coastal plain aids in understanding the geologic history of southeastern Virginia and northeastern North Carolina. Application of this model to the Shirley Formation (middle Pleistocene) and the Sedgefield and Lynnhaven members of the Tabb Formation (late Pleistocene) allows delineation of (1) the facies within, (2) the areal extent of, and (3) the landforms associated with these lithostratigraphic units.;Each lithostratigraphic unit corresponds to a separate marine transgression. Valleys formed during low stands of sea level subsequently widened and filled during the succeeding marine transgression. Coarse sediments accumulated along the shoreline as the sea advanced landward, forming a discontinuous sheet of basal lag deposits. Finer-grained deposits accumulated in estuaries or protected embayments and intertongue with or are covered by landward-migrating barrier deposits along the seaward margin of each lithostratigraphic unit. Three middle and late Pleistocene sea level oscillations are thus recorded in deposits of southeastern Virginia and northeastern North Carolina.;Facies within each lithostratigraphic unit consist of (1) a vertical succession from local, basal, channel-fill deposits and coarse, basal, lag deposits which grade upward into finer-grained deposits of estuaries or protected embayments or into medium to coarse sands of former barriers and (2) a lateral succession seaward from estuarine deposits to sediments of protected embayments and barriers. Sediment textures, sedimentary bedding-structures, fossils and plant detritus aid in interpreting paleoenvironments within each lithostratigraphic unit.