Late Pleistocene Estuarine Channel-Fill Sediments on the New Jersey Shelf: Response to Glacio-eustatic Sea Level Rise

The shallow New Jersey continental shelf has been an area of study for many decades. Evidence for the shelf's response to the Late Pleistocene glacio-eustatic sea level rise, confined principally to interpreted estuarine fill strata within fluvial channel systems, has been imaged extensively with high resolution chirp seismic data. However, little work has been done on sediment samples of these units. This study aids in the ground truthing of previous seismic stratigraphic work done on the New Jersey shelf channel-fill sediments by analyzing cores collected during the summer of 2007. The infilled channels from the study area are characterized as fossil riverine systems that developed on the exposed shelf during the Last Glacial Maximum lowstand ~18 ka. Subsequent sea level rise ~15-10 ka flooded and modified the valleys, forming estuaries. Allen and Posamentier's (1993) stratigraphic model of transgressive estuarine deposition posits the following ordered sequence: (1) a fluvial lag deposit, (2) estuarine mixed sands and muds (3) basin fill mud, and finally (4) estuarine mouth complex sediments. Seismic data over the buried channels on the outer New Jersey shelf (~80 m water depth) exhibit clearly identifiable seismic facies bounded by mostly horizontal boundaries that can be correlated to this interpretation (Nordfjord et al. 2006) We collected one core into these sediments, which likely sampled the estuarine mouth complex and basin fill muds. Previously collected cores supplement our analysis of these sediments. Seismic data over mid-shelf (~30 m water depth) valley channel fill stratigraphy is strikingly different, with finely-laminated U-shaped layering throughout the section, and often with cut-and-fill sequences. We collected 7 cores into these sediments. The cores ranged from 25cm to 5.8m in length. Thus far we have conducted grain size analysis via gross division of the percent of sand, silt, and clay. Initial results indicate that the laminated mid-shelf channel fill units are dominated by fine sands, suggesting a much higher-energy estuarine environment than when the outer-shelf channels were filled. Further grain size analysis will be conducted by sedigraph and settling tube. Radiocarbon analysis of the stratigraphy is being provided by the shell fragments and organic mud within the samples. We obtained one reliable shell fragment 14C date of 9389 ±79 years and eight bulk carbon 14C dates ranging from 10975 to 11445 years, with a strong terrestrial signature. The foraminiferal assemblages found within the sediment samples should eventually aid in determining the depositional environment.