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.
Paleontological data were collected using microscopes and recorded in the JRSO description software. All data for a species group (e.g., diatoms or nannofossils) were collected in a Microsoft Excel worksheet by hole. A zip file of the entire expedition's observations is also available.
We describe sedimentation on the storm-dominated, microtidal, continental shelf and slope of the eastern US passive continental margin between the Hudson and Wilmington canyons. Sediments here recorded sea-level changes over the past 100 myr and provide a classic example of the interplay among eustasy, tectonism and sedimentation. Long-term margin evolution reflects changes in morphology from a Late Cretaceous–Eocene ramp to Oligocene and younger prograding clinothem geometries, a transition found on several other margins. Deltaic systems influenced Cretaceous and Miocene sedimentation, but, in general, the Maastrichtian–Palaeogene shelf was starved of sediment. Pre-Pleistocene sequences follow a repetitive model, with fining- and coarsening-upward successions associated with transgressions and regressions, respectively. Pleistocene–Holocene sequences are generally quite thin (<20 m per sequence) and discontinuous beneath the modern shelf, reflecting starved sedimentation under high rates of eustatic change and low rates of subsidence. However, Pleistocene sequences can attain great thickness (hundreds of metres) beneath the outermost shelf and continental slope. Holocene sedimentation on the inner shelf reflects transgression, decelerating from rates of approximately 3–4 to around 2 mm a−1 from 5 to 2 ka. Modern shelf sedimentation primarily reflects palimpsest sand sheets plastered and reworked into geostrophically controlled nearshore and shelf shore-oblique sand ridges, and does not provide a good analogue for pre-Pleistocene deposition.
Integrated Ocean Drilling Program (IODP) Expedition 313 drilled three holes (Sites M27, M28, and M29; 34–36 m present water depth) across a series of prograding clinothems from the inner continental shelf of the New Jersey (USA) margin, a region that is sensitive to sea-level change. We examined 702 late Eocene to Miocene samples for benthic foraminiferal assemblages and planktonic foraminiferal abundances. We integrate our results with lithofacies to reconstruct paleobathymetry. Biofacies at all three sites indicate a long-term shallowing-upward trend as clinothems built seaward and sediment filled accommodation space. Patterns in biofacies and lithofacies indicate shallowing- and deepening-upward successions within individual sequences, providing the basis to recognize systems tracts, and therefore sequence stratigraphic relationships in early to early-middle Miocene sequences (ca. 23–13 Ma). The clinothem bottomsets and the lower portions of the foresets, which contain the thickest parts of clinothems, yield the deepest water biofacies. Shallower biofacies characterize the sequences in the upper portions of the clinothem foresets and on the topsets. Topsets are characterized by transgressive (TST) and highstand systems tracts (HST). Foresets contain lowstand systems tracts (LST), TSTs, and HSTs. Flooding surfaces mark parasequence boundaries within LSTs, TSTs, and HSTs. Superimposed on the long-term trends, short-term variations in paleowater depth are likely linked to global sea-level changes indicated by global oxygen isotopic variations.
One of ODP's long-standing goals has been to understand amplitudes and timing of global sea-level fluctuations. Past drilling expeditions have examined the sea-level record on carbonate platforms (e.g.• Legs 101. 115 and 133) and on atolls and guyots (e.g.• Legs 143 and 144). Passive margin transects have also been targeted for study, most recently a shelf/slope corridor offshore the Mid-Atlantic region of the eastern United States (slope drilled as Leg 150).
