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Eustatic Control of Slope Deposition: Inferences from Late Pleistocene Age Determinations and Seismic Character at ODP Site 1073, Offshore New Jersey Gregory S. Mountain 1 (914-365-8540; mountain@ldeo.columbia.edu) Cecilia M.G. McHugh 1,2 (718-997-3322; cmmqc@forbin.qc.edu) Hilary C. Olson 3 (512-471-0455; olson@utig.ig.utexas.edu) John E. Damuth 4 (817-272-2976; damuth@uta.edu) 1Lamont-Doherty Earth Observatory of Columbia University, Rt 9W , Palisades, NY 10964, United States 2S.E.E.S., Queens College C.U.N.Y., 65-30 Kissena Blvd., Flushing, NY 11367, United States 3Inst. for Geophysics Univ. of Texas at Austin, 4412 Spicewood Springs Rd., Austin, TX 78759-8500, United States 4Dept. of Geology Univ. of Texas at Arlington, 500 Yates St., Arlington, TX 76019-0049, United States The imprint of sea-level change on the stratigraphy of continental margins has been extensively studied for two decades. Much of this research has focused on shallow-water facies of siliciclastic shelves. Here we report on complementary analyses of a continental slope. Although this setting lacks direct indicators of sea-level change, our work shows that a surprisingly complete and discernible record of events can be recognized which have been removed from, or have not yet been documented, in studies of shallow-water shelves. Our research is based on MCS profiles linked to results of ODP Leg 174A on the outer shelf and upper slope offshore New Jersey. Age control on slopes is commonly poor because of reworking, massive sediment failure, and/or scarcity of diagnostic biostratigraphic indicators. Site 1073 (639 m water depth) is located 10's of km from modern canyons, and its 520 m of upper Pleistocene sediment (98.4\% recovery) provides good to excellent fossil abundance and preservation. Consequently we are able to determine ages to the sub-stage level with $\delta$O18 measurements of {\it G. inflata} tuned to SPECMAP and controlled by AMS C14, biostratigraphic, and paleomagnetic datum levels. Ages and recoveries at Sites 1071 and 1072 on the adjacent shelf are far less complete, but the seismic grid linking these regions provides the following inferences. The Pleistocene is represented by 4 major units that are largely incomplete and sand-prone on the shelf. Boundaries between these units were traced to Site 1073 where they mark hiatuses spanning times of rapid and large eustatic rises. The intervening accumulation rates varied from roughly 0.8 to several m/ka during stages 21-12, 9-8, 7-6, and 5-2. Four seismic facies are recognized: 1) a distinct reflecting surface at each boundary resulted from sediment starvation during large and rapid eustatic rises and the ensuing highstand; 2) weakly reflective sediments blanketed the mid-slope from highstand through early fall; 3) chaotic, discontinuous reflections from mass-transport deposits covered the paleoshelf edge and uppermost slope approaching times of maximum lowstand; and 4) coeval packages of distinct and continuous reflections developed downslope from these chaotic facies because of fine-grained fall-out. Reworked mineral and fossil assemblages, primary sedimentary structures, and wireline-log response at Site 1073 are consistent with these interpretations, and as will be discussed, provide new understanding of processes that controlled the adjacent shelf stratigraphy. |
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