VALLEY-FILL VERSUS INTERFLUVE: QUATERNARY DEPOSITIONAL PATTERNS RESULTING FROM SEA LEVEL FLUCTUATION, NORTHEASTERN NORTH CAROLINA

A detailed record of Late Quaternary sea level oscillations is preserved in the sediments underlying Croatan Sound, a drowned tributary of the Roanoke/Albemarle drainage system, northeastern North Carolina. Drill hole and high-resolution seismic data indicate that portions of 13 depositional sequences are preserved within the upper 45 m of deposits along an eight km transect across Croatan Sound. The antecedent topographic framework results in the preservation of two very different stratigraphic records along this transect. On the interfluves, similar marine deposits of different depositional sequences are typically stacked separated only by ravinement surfaces. However, within the paleo-drainages, these marine deposits are separated by non-marine and/or estuarine sediments deposited as channel-fill during periods of lowered sea level.

Sediment relationships within depositional sequences display vertical successions of as many as four major facies: fluvial/non-marine, estuarine, barrier island, and shallow marine. Foraminiferal and molluscan fossil assemblages indicate that the marine facies of these sequences were deposited in a shallow marine embayment with open connection to shelf waters. Each successive sequence modifies or truncates portions of the preceding sequence or sequences. Depositional sequence boundaries are the product of a combination of fluvial, estuarine, and marine erosional processes. Amino-acid racemization (AAR) has constrained the age of the ten uppermost depositional sequences to younger than 220 ka indicating that these depositional sequences do not each represent a complete interglacial, but rather are the result of multiple sea level oscillations within major interglacial stages.