ONSHORE-OFFSHORE CORRELATION OF QUATERNARY INCISED VALLEYS AND TIDAL PALEOCHANNELS, CAPE MAY, NJ

The Cape May peninsula in southern New Jersey is a Pleistocene spit complex built across Delaware Bay. Incision of the Delaware River during the MIS 6 lowstand carved a paleovalley that was filled with estuarine and beach sediment during MIS 5. Southward spit growth during MIS 5 forced the MIS 4-2 Delaware channel south of Cape May. We report on seismic surveys on the inner shelf that trace the MIS 6 paleovalley seaward, and image MIS 4 and MIS 2 channels of tidal or local fluvial origin.

We identified 4 major erosional reflectors. Vibracores aided in characterization of sediment and age dating the upper two surfaces which were tied to onshore wells where possible. The youngest seismic reflector, interpreted as the transgressive ravinement surface, images shallow incisions infilled by sands and locally capped by active sandy shoals or wave ripple fields of 1-2 m amplitude in the bay mouth. Beneath this reflector interbedded sand and clay units occur either infilling older incised valleys or as extensive horizontal sheets. Organics within the clay layers yield calibrated radiocarbon ages of 4930 +/- 40 to 6110 +/- 30 BP at depths of 9.8 m and 13.5 m respectively. Below the second erosional reflector, in some locations as shallow as 13.8 m are weathering-stained sands and clays with radiocarbon dates of >40,500 BP which have also been identified farther north in coastal NJ. This prominent, laterally extensive seismic reflector is interpreted as the MIS 2 lowstand surface.

We identify two additional erosional surfaces of MIS 4 and MIS 6 ages that tie to existing marine seismic and age-dated cores to the north. We track a broad paleovalley that ties to the MIS 6 onshore paleovalley located using downhole geophysical logs. This MIS 6 valley projects westward to an incised valley previously identified by seismic surveys in Delaware Bay. We observe a number of smaller meandering MIS 4 channels of probable tidal origin that flank and re-incise the MIS 6 valley.

In the baymouth off the tip of Cape May, seismic data reveal MIS 2 channels that truncate older ones and step bayward. Shoal features or wave ripple complexes showing bayward transport directly overlie the MIS 2 channels.