Assessing the significance of along-strike variations of middle to late Miocene prograding clinoformal sequence geometries beneath the New Jersey continental shelf

Seismic mapping of high-resolution multichannel seismic profiles along the New Jersey margin illustrates how characteristics of middle–late Miocene clinoformal sequence boundaries (SBs) change markedly along strike in presumed response to local depositional and erosional processes. Most SBs converge from SW to NE, in part as a result of the influence of underlying basin morphology on accommodation space, but also in response to differential subsidence and presumed along-strike variations in sediment supply from the adjacent margin. The curvature of clinoform breaks, historically viewed as marking palaeo-shelf edges, is variable and such breaks are rarely sharp. Gently curved palaeo-shelf/slope transitions cannot be assigned precise palaeobathymetric significance and probably instead reflect post-depositional sediment reworking. The amount of erosional truncation landward of clinoform breaks varies significantly. Documented along-strike variability in SB morphology occurs, even though middle–late Miocene palaeo-shelf edges are nearly linear in plan view. Therefore, such linearity cannot be a product of uniform sedimentary processes and/or accumulation along strike, but instead reflects elongation of depocentres of originally variable cross-sectional geometry, possibly with the assistance of along-strike currents. The observed lateral geometric heterogeneity of Neogene sequences can exert profound and unwanted influences on the outcome of scientific drilling intended to calibrate seismic stratigraphic interpretations in the absence of sufficient three-dimensional (3D) seismic control.