STRATIGRAPHIC FRAMEWORK AND CONTROLS ON THE QUATERNARY EVOLUTION OF THE MID-ATLANTIC PASSIVE MARGIN; CAPE HATTERAS REGION, NORTH CAROLINA, USA

New seismic and core data, combined with amino acid racemization age data, define the sequence stratigraphic framework and geologic controls on Quaternary development of the mid-Atlantic continental margin, in the Cape Hatteras region. The sequence stratigraphic framework generally reveals multiple thin (ca. 5 to 10 m thick) depositional sequences responding to shoaling and progradation of the margin, changes in amplitude and frequency of sea-level oscillations during the mid-Pleistocene, and possibly boundary current interactions with the margin. Two supersequences of early and late Pleistocene age are defined. The early Pleistocene supersequence comprises inner shelf to deep shelf deposits dominated by Type 2 unconformities and drift sediments (contour-parallel, elongate mounded deposits ca. 2 km in width by 20 m in height). The early Pleistocene shelf occurs at a depth of ca. 20-40 m beneath the modern estuarine system (the Pamlico Sound) and is characterized by stacked inner shelf deposits originating from sediment sources to the west. A break in the shelf geometry occurs beneath central Pamlico Sound at a depth of ca. 40 m, and is characterized by an abrupt increase in slope and clinoform packages indicating forced regressions. Seismic and foraminiferal paleoevironmental data from cores indicate the occurrence of early Pleistocene lowstand shoreline deposits on this paleo-topographic break. A shelf terrace with drift deposits occurs at a deeper level (ca. 70 m) beneath the modern barrier island system. Type 2 boundaries indicate minimal exposure of the terrace during early Pleistocene lowstands, and attest to low amplitude sea-level changes. Drift deposits were likely active during early Pleistocene highstands. The late Pleistocene supersequence comprises middle to inner shelf and paralic deposits that are incised by multiple fluvial valley systems defining Type 1 unconformities. The deep (>40 m) incision of these valleys indicates a downward shift in sea-level position during lowstands. A well-developed fluvial valley system, in the southern region of the study area, exhibits multiple cut-and-fill units indicating a prolonged dominance over shelf drainage patterns in the region, and valley reoccupation during successive sea level lowstands.