Seismic anatomy of Miocene clinoform sequences on the New Jersey (USA) shelf, and implications for sediment transport during base-level rhythms

Abstract The New Jersey, USA, continental margin has become a natural laboratory for studying sediment dynamics and sequence architecture associated with eustatic rhythms. We collected 564 km2 of ultrahigh-resolution 3-D seismic data in the region of Integrated Ocean Drilling Program Expedition 313 to investigate the formation of the shelf and clinoform system during early to middle Miocene time. We identified 22 high-frequency sequences and 76 systems tracts, using a geometric breakdown approach based on changes in the landward and seaward terminations and elevation of clinoform rollovers in successive reflector packages. Predicted petrophysical properties of acoustic impedance, P-wave velocity, density, and clay content show rhythmic patterns that follow the seismic sequence architecture, with landward fining in transgressive deposits and basinward fining in other systems tracts. Similar proportions of lowstand, transgressive, and highstand deposits suggest that sediment accumulated during periods of both rise and fall in relative sea level, with a low proportion of falling-stage deposits (4%), which suggests that forced regression rarely exposed clinoform breakpoints. Maximum dip azimuths for the Miocene section indicate southwestward sediment transport, broadly along strike of the margin. Enhanced sediment accumulation to the southwest caused a 13° anticlockwise rotation in clinoform orientation after the late Oligocene, and this uneven stress load influenced the orientation of contemporary polygonal faults on basinward parts of the clinoforms. In contrast to models that emphasize downslope sediment transport in margin development, we highlight the importance of along-shore advective processes in shaping the New Jersey margin during the Miocene.