Seismic Stratigraphy Since the Late Miocene of the Near Shore New Jersey Margin Between Barnegat and Manasquan Inlets, New Jersey

English Abstract:

In the summer of 2013, researchers from Rutgers University and the New Jersey Geological and Water Survey conducted 590 km of boomer seismic profiles 0-6 miles off the NJ coast between Barnegat and Manasquan Inlets. In the fall of 2014, 30 vibracores were taken to determine stratal relationships correlated to the seismic data. The seismic data show three main depositional units. The oldest unit is comprised of Upper Miocene fine quartz sand and silt with occasional interbedded clay layers, and characterized by prominent parallel reflectors that dip southeast. These strata are capped by an erosional surface that dips south-southeast and crops out at the seafloor near the northern extent of the survey area. This surface is overlain by as much as 20 m of complexly arranged Pleistocene gravels, sands and silts with irregular reflectors traceable for distances of only 0.5 km or less. NE-trending Holocene ridges detached from the shoreface comprise the third and youngest depositional unit. Most ridges are isolated elongate features 5-10 km long and 1 km wide. All rest on a level reflector separating them from Pleistocene strata in most of the survey area, and from Miocene strata along the northern limit. The ridges are relict late-Pleistocene light grayish-white, well-sorted, fine-grained quartz sand deposited during periods of episodic sea level rise since the last glacial maximum and reworked by present day hydrodynamics. The parallel dipping reflectors of the Miocene suggest continuous delta-front marine deposition. Glacially-forced post-Miocene sea-level fall cut deeply into these strata, and sediments were not preserved at this nearshore location again until Late Pleistocene. Transgression since the Last Glacial Maximum and development of the adjacent barrier island landscape has resulted in minimal new sediment contribution to the nearshore. In its absence, relict sands have been reworked into ridges under a complex interplay involving ebb-tidal deltas, storms and longshore currents.