EUSTATIC HISTORY, SEQUENCE ARCHITECTURE, AND LITHOFACIES SUCCESSIONS ALONG THE NJ TRANSECT: A PROGRESS REPORT

IODP Expedition 313 drilled & logged 3 sites in 35 m of water 45-65 km off New Jersey in May-July 2009. These data constitute a long-awaited 'missing link' in a transect of sites from the coastal plain to the continental slope begun in 1993 to 1) calibrate the imprint of baselevel changes on sequence architecture & lithofacies successions, & 2) extract global sea-level history during times of known glaciation. Exp313 sites were located at the rollovers of Oligocene to mid-Miocene clinoforms where this record would be most clearly expressed & was feasible to drill. The tasks of evaluating sequence stratigraphic models, comparing the age of inferred sea-level falls to the δ¹⁸O glacio-eustatic proxy, & estimating the corresponding amplitudes, rates & mechanisms of sea-level change await the completion of several underway studies; here we provide a progress report.

1311 m of very good to excellent quality cores were collected with 80% recovery. The deepest was 757 mbsf; the oldest was upper Eocene. Each hole was located to intersect top-, fore- &/or toeset strata of several clinoforms linked by a grid of high-resolution 2D seismic profiles. Slim-line logs in each hole gathered spectral gamma ray, resistivity, magnetic susceptibility, sonic & acoustic televiewer measurements.

Seismic-log-core correlations, strengthened by MultiSensorCoreLogger measurements, enable us to locate samples in the seismic framework with depth uncertainties of only a few meters. Thus we're able to ground-truth lithofacies at a variety of settings in several depositional sequences. Topsets were well sorted silts & sands deposited in offshore to wave- & river-dominated shoreface settings. Toeset silts & silty clays were deposited below storm wave base & typically interbedded with poorly sorted debrites & turbidites deposited at times of clinoform degradation. Geochronologies based on Sr-isotopic ages, biostratigraphy, limited magnetic reversals & pollen markers show accumulation rates of 50-150 m/my with hiatuses across sequence boundaries from 0 to ~2 Ma. No conclusive evidence has been found of a sea-level fall below a clinoform rollover, but shoreface deposits along clinoform foresets paired with deep-water facies in topsets of the same sequence imply changes in relative sea level on the order of 60 m.

IODP Exp313 Scientific Party, coauthors