ABSTRACT: Clastic Sequences Developed During Glacio-Eustatic Sea Level Fluctuations on a Sandy Barrier Coastline

Gail M. Ashley, R. E. Sheridan, R. W. Wellner

Seismic reflection (Geopulse^TM) profiles from a 125 km² grid on the New Jersey low-mesotidal sandy barrier coastline reveal a 30-m sediment thickness composed of three unconformity bounded parasequences. Vibracores from 12 sites reveal a variety of depositional environments that existed during the most recent glacio-eustatic sea level fluctuations on this stable passive margin. Environments include fluvial, during glacial lowstands; barrier islands with back-barrier lagoons and pro-barrier ebb tidal deltas and shore-attached ridges; and below storm-wave base shelves during interglacial highstands. Following the last major interglacial (Sangamon, ^approx125KA), sea level fell and rivers eroded a planar seaward-dipping surface by the early Wisconsinan ime (^approx70KA). As sea level rose during the mid-Wisconsinan (^approx50KA), a barrier island shoreline migrated to within 0.2-1.7 km of the modern shoreline. Maximum highstand of mid Wisconsinan sea level was 20 m below present. Sea level fell again during the late Wisconsinan (^approx20KA). A barrier island/lagoonal system developed under rising sea level at least by the early middle Holocene based on peats (8800 BP) in lagoonal muds cored from -12 m. The root of the mid-Wisconsinan barrier system was preserved under early Holocene transgressive sediments. The modern coastal and inner continental shelf deposits are relatively thin (3-4 m) pebbly sands overlying a prominent ravinement surface unconformity formed during the Holocene sea level rise. Isopach maps constructed for this sur ace indicate up to 7 m of relief eroded into muds beneath the ebb tidal delta and the shore-attached ridges. The ridges and delta shielded the underlying fine sediments during sea level rise. Based on a reasonable Atlantic shoreline transgression rate of 2 m/yr, the modern Barnegat Inlet ebb tidal delta has existed in its general location for at least 800 years.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990