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doi:10.2204/iodp.proc.313.101.2010 Expedition 313 summary1Expedition 313 Scientists2AbstractIntegrated Ocean Drilling Program (IODP) Expedition 313 to the New Jersey Shallow Shelf off the east coast of the United States is the third IODP expedition to use a mission-specific platform. It was conducted by the European Consortium for Ocean Research Drilling (ECORD) Science Operator (ESO) between 30 April and 17 July 2009, with additional support from the International Continental Scientific Drilling Program (ICDP). There were three objectives: (1) date late Paleogene–Neogene depositional sequences and compare ages of unconformable surfaces that divide these sequences with times of sea level lowerings predicted from the δ18O glacio-eustatic proxy; (2) estimate the corresponding amplitudes, rates, and mechanisms of sea level change; and (3) evaluate sequence stratigraphic facies models that predict depositional environments, sediment compositions, and stratal geometries in response to sea level change. We drilled at three locations in around 35 m of water 45–67 km offshore, targeting the topsets, foresets, and toesets of several clinoforms at 180–750 meters below seafloor (mbsf). Seismic correlations to previously drilled holes on the continental slope and extrapolations of depths to key horizons in wells drilled into the adjacent coastal plain suggest the clinoform structures investigated during Expedition 313 were deposited during times of oscillations in global sea level; however, this needs to be determined with much greater certainty. The age, lithofacies, and core-log-seismic correlations provided by drilling at key locations will yield the data needed for a rigorous evaluation. We attempted 612 core runs with 80% recovery totaling 1311 m in length. Some or all of the upper 180–280 m of sand-prone sediment was drilled without coring. The deepest hole (M0029A) reached 757 mbsf, and the oldest sediment recovered was late Eocene (Hole M0027A). Wireline logs gathered spectral gamma ray, resistivity, magnetic susceptibility, sonic, and acoustic televiewer data; a vertical seismic profile was run at each site. Multisensor core logger (MSCL), natural gamma ray, and thermal conductivity measurements were made on all cores prior to splitting. Aided by physical properties of discrete samples measured onshore, we have established preliminary core-log-seismic ties with depth uncertainties typically ±7 m or less. We are confident that further study will narrow this range and firmly link facies successions to as many as 16 surfaces and/or sequence-bounding unconformities mapped in the regional seismic grid. Eight lithologic units are recognized that contain important physical and biofacies indicators of paleobathymetry. Reliable zonations of multiple fossil groups, Sr isotopic ages measured on mollusks and foraminifers, and intervals of magnetic reversal chronology provide a nearly continuous composite record of ~1 m.y. sea level cycles (22–12 Ma). Shifts in climate on the adjacent coastal plain provide distinct pollen markers in all three holes and represent another correlation tool. We recovered regressive sediment bodies that are absent in onshore boreholes because of those updip locations. Lithofacies and benthic foraminifer assemblages provide a rich source of information concerning depositional setting and imply as much as 60 m water depth changes; calculations of sediment compaction, crustal loading, and other corrections need to be made before we can estimate the corresponding magnitudes of eustatic change. Large variations in pore water salinity appear to be controlled by lithofacies. Their sharp vertical gradients await explanation, and relationships to microbiologic communities that we recovered from unsplit cores have yet to be determined. |
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