Shoreface sedimentation in southeastern North Carolin

The geologic framework and surficial morphology of the shoreface and inner shelf off Wrightsville Beach, North Carolina have been mapped using high-resolution sidescan-sonar, bathymetric, and seismic-reflection surveying techniques, a suite of over 200 diver-vibracores, and sea-floor observations by divers. The inner shelf is an active surface of marine erosion; modern sediments, where present, form a thin, patchy veneer blanketing Tertiary and Quaternary units. The lithology of the underlying units exerts a primary control on inner shelf bathymetry, as well as on the texture and composition of surficial sediments.;Remnants of a discrete early Holocene (8-9 ka) barrier-lagoon complex are present on the inner shelf. The preservation of this sequence is attributed to a catastrophic, meter-scale rise in sea level that occurred around 7.6 ka. Barrier island migration since about 6 ka has been slow, and is attributed to a reduced rate of sea-level rise, coupled with the erosion and maturation by steepening of an initially broad, shallow shoreface.;The Wrightsville Beach shoreface is dominated by a linear, cross-shore morphology of rippled scour depressions (RSDs) extending from just seaward of the surf zone onto the inner shelf. The formation of RSDs is probably related to pre-existing topographic and grain-size variations that result in preferential erosion of material within coarse substrates. The gross morphology of the sea floor has not changed over a five-year observation period, despite several extreme storm events. This suggests that the present sea-floor morphology represents a recurring, preferential state. This stability is perhaps the result of interactions at several scales that contribute to a repeating, self-reinforcing pattern of forcing and sedimentary response.;Over 30 years of intensive beach replenishment at Wrightsville Beach appears to have exceeded shoreface accommodation space, resulting in the leaking of beach and shoreface sediment to the inner shelf. A macroscopically identifiable beach replenishment sediment on the shoreface and inner shelf has been used to identify the decadal-scale pattern of sediment dispersal. The replenishment sediment is present as a seaward-thinning wedge that extends onto the inner shelf. This wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach replenishment.