MULTIPLE STAGE 5 HIGHSTANDS ON THE SOUTHERN NEW JERSEY COASTAL PLAIN: LATE PLEISTOCENE ALLOSTRATIGRAPHY OF THE NORTHERN DELAWARE BAY MARGIN

Previous investigations of the Late Pleistocene Cape May Formation in southern New Jersey revealed six global climate-induced, sea-level highstand sequences, forming two composite terraces along the northern margin of Delaware Bay (O’Neal, 1997; O’Neal and McGeary, in press). O’Neal et al. (2000) used aminostratigraphic evidence to correlate these highstand deposits with marine oxygen isotope stages 13, 11, 9 (two phases), 7, and substage 5e. In this investigation, we present lithologic and ground penetrating radar evidence for two additional, thin (3 m or less) estuary-margin highstand deposits of possible substage 5a or 5c age. These units are defined as allostratigraphic deposits that are stratigraphically younger than the substage 5e deposits that subcrop beneath the lower terrace, and stratigraphically older than the Holocene transgressive surface mapped by Dunn (1998).

The thin nature of these sand-dominated highstand deposits, combined with the preservation of stranded regressive beach-ridges, suggests fairly rapid rise and fall of global eustatic sea level during minor deviations in the general degradation of global climate between substage 5e and the last glacial maximum (Wisconsin). Based on relative stratigraphic position and overall geometry, we tentatively assign ages of substage 5a or 5c to these allostratigraphic units representative of post-(peak)substage 5e deposition. This age assignment is significant in that emergent highstand deposits younger than substage 5e are not widely recognized in the mid-Atlantic Coastal Plain. Additionally, aminostratigraphic techniques useful for the age estimation of older Pleistocene highstand deposits in this region have problematically relied upon U-series calibration dates of approximately 80 ka (5a age) from corals retrieved from broadly-interpreted stage 5 deposits in southeastern Virginia and central South Carolina (summarized in Wehmiller and Miller, 2000). Optically stimulated luminescence analyses (in progress) of quartz grains from the 5a/5c(?) southern New Jersey deposits should provide an important reference point for the resolution of these problems in mid-Atlantic Coastal Plain Pleistocene highstand stratigraphy.