Abstract
Sedimentation on the Pleistocene New Jersey (NJ) shelf is complex, and results from the interaction of processes chiefly driven by glacioeustatic change. Erosion, non-deposition, downcutting and infilling combine to produce a complicated set of reflectors and sedimentary units that are best interpreted in the shallow subsurface with the aid of high resolution seismic reflection profiling. The highly variable lithology on the shelf has historically been an impediment to significant core recovery in this challenging environment. Coring using the AHC-800 drilling system provided continuous downcore recovery at three sites on the outer shelf. The sites targeted fluvial incisions, channel fill and exposure surfaces associated with glacial lowstands. The exceptional cores were analyzed using an integrated approach. Textural and benthic foraminiferal data were evaluated to determine the environment of deposition and estimate paleodepth. Carbon dating of wood and shell material provides the temporal framework for interpretation and K–Ar dating of hornblende crystals provides insights into the source region of sediments.
Our integrated analysis indicates the NJ shelf was a dynamic environment from at least 45ka. Estimates of sea level from this study are consistent with other studies from the Pleistocene NJ Margin. The oldest sediments (>36k.y.) recovered by drilling came from below (Site 3) and above (Site 1) R, a time-transgressive regional unconformity. Best estimates are for formation of R on the mid shelf, between MIS3b and the MIS3b/a transition, ~45ka, under neritic conditions. Channels were incised during late MIS2, between ~30 and 16ka. Channel infill was focused in a narrow time frame, during latest MIS 2 (16–14ka), shortly after the shoreline began to migrate landward. Rates of 1–2cm/yr are consistent with modern fluvial/ estuarine sedimentation rates. Reinvigoration and infilling of the channels around 14ka is associated with meltwater pulse 1A. We find no evidence at our study area for jökelhlaup deposition associated with the Intra-Allerød cold period ~13ka. Regional deposition (channel infill and interfluvial regions) was underway by latest MIS2/early MIS1 as sea level transgressed the shelf. The uppermost sediments are of Holocene to Recent age and are routinely and likely rapidly reworked, eroded and mixed by shelf processes. The sediment source during MIS3, as determined by hornblende age dates, was bimodal. Older sediments were derived from the Reading Prong/NJ Highlands and younger sediments were sourced from along the Hudson River. Delivery to the study area was through a more southerly paleo-Hudson position that may have resulted in formation of the outer shelf wedge through deltaic sedimentation during at least MIS 3b–3a.
► We present results from coring of the late Pleistocene middle to outer New Jersey (NJ) shelf. ► Fluvial incision associated with glaciation occurred between ~30 and 16ka. ► Incision was followed by rapid infilling in latest MIS2, at the time of MWP1a.