LATE PLEISTOCENE FACIES DISTRIBUTION, SEA-LEVEL CHANGES, AND PALEOGEOGRAPHY OF THE INNER CONTINENTAL SHELF OFF LONG BEACH ISLAND, NEW JERSEY

This analysis of high-resolution shallow seismic data, vibracores, conventional radiocarbon and amino-acid racemization (AAR) dating of sediment samples determines the late Pleistocene facies distribution, sea-level changes and paleogeography of a 124 km2 area offshore Long Beach Island, New Jersey. In this passive margin setting, the combined effects of high-magnitude sea-level change (~70 to 120 meters) and low subsidence rate (limited accommodation space) result in incomplete stratigraphic packages on the inner shelf. This study examines Oxygen Isotope Stage (OIS) 1, 3, and 5 sequences and sea-level changes during OIS 3 and 5.

Contour plots of seismic reflector surfaces and isopachs, combined with sequence stratigraphic analysis reveal 1) a bay-mouth shoal complex in OIS 5 deposits; 2) a paleo shoreline in nearshore OIS 3c deposits; 3) Holocene shoals/swale topography; and 4) Pleistocene buttes (remnants of OIS 3 deposits cut by sub-aerial erosion and submarine currents). The large channel in the OIS 5 sequence is interpreted as comparable in size and internal structure to the modern Delaware shelf valley, with multiple channels 2-5 km in width and with 5 - 12 m of remaining valley fill sediments.

Steep seaward dipping reflectors located approximately 1.5 to 5 km from the present shoreline are interpreted as a barrier island/shoreface system, the top of which is found at water depths of ~15 to 19 m, pinning the 55 ka OIS 3c highstand. The mid-Wisconsinan shoreline previously reported more inshore and near Barnegat Inlet is re-interpreted as an OIS 5b feature, based on correlation of the Area C seismic data and tied to radiocarbon and AAR dates from cores.

The positive depositional features in the OIS 2/1 sediments are shore-detached ridges separated by wave- and current-eroded valleys.

In sequence stratigraphic terms, type 1 sequences predominate. In this inner shelf setting, the transgressive systems tract is the best-preserved part of the sequence.