ANTECEDENT TOPOGRAPHIC CONTROLS OF THE HOLOCENE BARRIER ISLAND--ESTUARINE SYSTEM EVOLUTION, NORTHEASTERN NORTH CAROLINA

The objectives of an ongoing USGS-ECU-NCGS cooperative research program are to delineate the geologic framework, develop the detailed evolutionary history, and define the process dynamics driving the rapidly changing, high-energy coastal system of NE North Carolina. Integration of sedimentological, geophysical, and chronostratigraphic data has led to understanding the interplay between Holocene sea-level history and the geometry and composition of the Pleistocene geologic framework. The antecedent Pleistocene topography is a collage of shore-perpendicular drainage basins with a network of shore parallel tributaries, which formed during glacial lowstands. As the ongoing transgression floods across these drainage basins, the following evolutionary shoreline stages are recognized. 1) As rising sea level floods up the drainages, oceanic and/or estuarine strandplain beaches form on flanks of the antecedent interstream divides. 2) When sea level reaches the top of broad interstream divides, a paired oceanic and estuarine barrier island system form on opposite sides of the divide separated by an interior lagoon on the divide crest. 3) As sea level overtops the interstream divide, the estuarine barrier collapses into a large shoal system and a single, wide, overwash-dominated, oceanic barrier develops on the ocean side. These classic rollover barriers occur on top of the interstream divide and are characterized by broad interior flats, marsh platforms, and back-barrier berms and shoals. 4) Where a large estuarine body exists behind the oceanic barrier and sea level continues to rise, the barrier system will collapse into the estuarine basin resulting in very shallow, open marine embayment that floods the outer Coastal Plain. A large portion of the Pleistocene stratigraphic record in NE NC is characterized by this depositional setting. 5) Where adequate sand supplies exist along the mainland shore of the marine embayment, smaller-scale strandplain beaches and/or barrier island systems form through back-stepping processes.