Delta progradation and channel drainage systems from the early miocene to the present day between Barnegat and Manasquan Inlets, New Jersey

Nearshore seismic and core data were collected in 2013-14 for beach replenishment assessment between Barnegat and Manasquan Inlets by the New Jersey Geological and Water Survey. Analyses described in the following study reveal upper-middle Miocene deltaic progradation originating from a fluvial point-source northwest of the survey grid overlain by a network of channel drainage systems. Previous studies have identified both Miocene deltaic and channel deposits along the New Jersey margin, but efforts to map individual deltaic progradation sequences and channel paths have been limited by wide seismic grid spacing. In addition, Pleistocene sea-level variations have eroded much of the inner New Jersey shelf, making it difficult to reconstruct the highly discontinuous stratigraphic record without dense line spacing and reliable control by selective coring.;Five depositional units are identified as lower-middle Miocene deltaic deposits (Unit I), upper Pliocene-upper Pleistocene fluvial channel deposits (Units II, III), upper Pleistocene MIC 3 lowstand deposits (Unit IV), and Holocene ridge sand and estuarine mud (Unit V). With the exception of Unit I, depositional units are bounded above and below by transgressive surfaces: Surfaces 2 and 3 mark the base of the channels that formed Units II and III, Surface 4 underlies Unit IV sediment and is an erosional unconformity formed during the MIC 4 sea-level lowstand, and Surface 5 is a subhorizontal unconformity formed since the Last Glacial Maximum (LGM) underlying the most recent Unit V material. Because Unit I extends beyond the 0.1-second recording length of seismic data examined in this study, no surface bounds Unit I below and instead prominent, individual seaward dipping reflectors within Unit I are traced throughout the study area. These intra-Unit 1 reflectors map Miocene deltaic clinoform progradation across the study area and reveal geographic patterns that potentially influenced the preferential incisive behavior of subsequent channel drainage systems that formed during periods of sea-level lowstands as early as the late Pliocene.