THE RECORD OF QUATERNARY SEA-LEVEL CHANGE, NORTH CAROLINA COASTAL PLAIN, MID-ATLANTIC US

The Albemarle Embayment of northeastern North Carolina contains a thick section (up to 60 m) of Quaternary strata that preserve a complex history of sea-level change and coastal evolution over the past million years. A detailed study of the geologic framework of this segment of the coastal plain is now underway, using a variety of geophysical, geochemical, litho- and bio-stratigraphic tools, under the auspices of a cooperative research program of the U.S. Geological Survey, the North Carolina Geological Survey and several academic institutions. Eight core holes up to 65 m deep were drilled on the northern Outer Banks (75.6W, 35.8N) in 2002; a similar number will be drilled in 2003. Over 7200 km of seismic lines in estuarine, back-barrier, and inner shelf environments, and 500 km of ground-penetrating radar lines along the coastal barriers, combined with stratigraphic and paleoenvironmental analysis of cores, record a history of mid- to late-Pleistocene valley incision and sedimentation during regression/transgression cycles. Seismic and sidescan sonar data combined with ~200 vibracores from the inner shelf, indicate that the distribution of Recent sediment (above the Holocene ravinement surface) on the shoreface and inner continental shelf is patchy and controlled by the underlying geologic framework, which also influences the geomorphology of the overall barrier island system. In many locations, Pleistocene (or older) deposits are exposed on the shelf or shoreface. We derived age estimates (ranging from ~100 ka to ~1,000 ka) for Pleistocene units from molluscan amino acid racemization data, which broadly define aminozones or discrete intervals of deposition. Aminozones recognized in subsurface sections are represented by transported fossil material found on beaches or both in-place and reworked material on the inner shelf. The late Quaternary record includes a valley-fill sequence associated with the paleo-Roanoke River and its tributaries, which is incised into the underlying Pleistocene deposits. This sequence ranges from ~3 m to >30 m in thickness; seismic stratigraphy and radiocarbon ages indicate at least six distinct phases of deposition since the last glacial maximum.