Clastic sequences developed during late Quaternary glacio-eustatic sea-level fluctuations on a passive margin: Example from the inner continental shelf near Barnegat Inlet, New Jersey

Abstract

Analysis of 100 km of seismic reflection (GEOPULSE) profiles from a 47-km 2 grid on the New Jersey low-mesotidal inner continental shelf near Barnegat Inlet reveals that the upper 30 m is composed of 3 unconformity-bounded units. Vibracores (1-6 m long) recovered from 12 sites contain several lithofacies, reflecting a variety of depositional environments that existed during late Quaternary glacioeustatic sea-level fluctuations on this slowly subsiding passive margin with low sediment supply. Environments include rivers during glacial and stadial lowstands of the sea, and a barrier island-lagoon complex, as well as pro-barrier ebb-tidal delta, shore-attached and -detached ridges, and below storm-wave-base shelf during interglacial or inter-stadial highstands. Following the last major interglacial (∼125 ka), sea level fell and rivers eroded a planar, seaward-dipping surface (R1) by early Wisconsinan time (∼70 ka). As sea level rose during the mid-Wisconsinan (∼55 ka), a barrier island system migrated to within 0.2-1.7 km of the modern barrier shoreline, leaving a 4- to 6-m-thick record (depositional sequence I). Maximum highstand of the mid- Wisconsinan sea level was 20 m below present. Sea level fell again during the late Wisconsinan (∼20 ka), and rivers again flowed across the exposed shelf, creating an unconformity (R2). A barrier/lagoonal system developed under rising sea level by at least early middle Holocene time, based on peats (8810 ± 170 yr B.P.) cored from -12 m. The mid-Wisconsinan (∼55 ka) barrier system was preserved under these early Holocene transgressive sediments (lower unit of depositional sequence II, lower transgressive tract). The modern barrier and inner continental shelf deposits (upper unit of depositional sequence II, upper transgressive tract) are relatively thin (average 3-4 m) pebbly sands overlying a prominent unconformity (a transgressive surface, R3) formed by marine erosion during the Holocene sea-level rise. Both the ebb-tidal delta and shore-attached linear sand ridges act as partial shields to wave and tidal- current erosion of the muddy sub-strate below R3. In the nearshore area, this shielding is creating a transgressive surface (marine unconformity) of relatively high relief (3-7 m).