Abstract:
We report preliminary results of IODP Expedition 313 that drilled and logged 3 sites in 35 m of water 45-65 km offshore New Jersey in May-July 2009. Cores were split, sampled and analyzed at the Bremen Core Repository in November 2009. These data constitute the long-awaited "missing link" in a transect of sites begun in 1993 by IODP/ICDP to recover Oligocene-Miocene sea-level history from the NJ coastal plain to the continental slope. The goal is to: (1) compare the age of base-level changes with the age of sea-level lowerings predicted by the delta 18O glacio-eustatic proxy; (2) estimate the corresponding amplitudes, rates and mechanisms of sea-level change during this time of Earth's "Icehouse"; and (3) evaluate models that predict lithofacies successions, depositional environments and the arrangement of seismic reflections in response to sea-level change. We collected 1311 m of very good to excellent quality core with 80% recovery. The deepest hole was 757 mbsf; the oldest sediment was upper Eocene. Slim-line logs gathered spectral gamma ray, resistivity, magnetic susceptibility, sonic and acoustic televiewer measurements. Porewater was sampled at all depths at each site; uncontaminated sediments were frozen for microbiologic studies yet to be done. The strategy of using 3 sites to sample clinoform topsets, foresets and toesets paid off. Downhole logs, multi-track measurements of unsplit cores, and physical properties of discrete samples provide core-log-seismic ties with depth uncertainties of roughly + or - 5 m or less. Further study will narrow this range and confidently link strata to as many as 16 regional surfaces/unconformities mapped in an accompanying seismic grid. Excellent paleontologic zonations plus Sr-isotopic ages reveal a nearly continuous composite record of approximately 1 myr sea-level cycles 22-12 Ma. Facies and benthic foram assemblages imply water depth changes of 60-100 m within transgressive-regressive cycles in topset beds. When all features are correlated between sites and backstripped to recover original geometries, this tight integration promises to provide reliable estimates of eustatic magnitudes. Large variations in porewater salinity are clearly controlled by facies. Their sharp vertical gradients await explanation, and relationships to microbiologic communities have yet to be determined.