Abstract:
Seismic profiling and drilling have established the New Jersey continental margin as a natural laboratory for sequence stratigraphic studies. Insights into margin evolution, the history of sea-level change, and the distribution of facies within layered rocks will be tested in 2007 when IODP drills 3 wells in the inner Jersey Shelf. Regional seismic surveys in the 1970's revealed depositional sequences identified by clinoform geometries and associated onlap, downlap and offlap. ODP Leg 150 (1993) sampled their downdip extremities on the continental slope, and determined they are mostly lower and middle Miocene with stratal gaps consistent with glacially forced falls in global sea level. ODP Legs 150X and 174AX (1993-2003) recovered correlative updip sediments beneath the New Jersey coastal plain and provided strong evidence of links between facies successions and glacioeustatic change. However, no drill holes sampled Miocene sequences beneath the inner shelf where they are their thickest, the imprint of sea-level change is most clearly recorded, and the ties between facies distribution and sequence architecture can be firmly established. Recent high-resolution seismic profiles provide the best tie between existing onshore samples and offshore images. These profiles reveal sequence geometries consistent with a wave-dominated deltaic model that is further supported by facies recovered from adjacent onshore cores. These and other high-resolution seismic data along the Jersey Shelf indicate that variations in accommodation space and sediment supply caused localized sequence preservation and/or cutout, and as a result, not all seismic sequences project to every onshore corehole. Sequence amalgamation also occurs down dip with the result that many sequences are not found on the slope. Even so, we have correlated geophysical logs at the onshore wells to similar logs collected in 3 sparsely sampled boreholes drilled previously on the inner shelf. We correlated these offshore logs to the high-resolution seismic data, creating the first direct tie between onshore wells and offshore profiles. We can now develop greatly improved predictions of the facies, age, and paleoenvironmental origin of seismic sequences that comprise the lower and middle Miocene New Jersey Shelf targeted for drilling by IODP Expedition 313.