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Eastern Mississippi delta: late Wisconsin unconformity, overlying transgressive facies, sea level and subsidence |
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| Authors: | Daniel Jean Stanley Andrew G Warne and Joseph B Dunbar |
| Institution: | aDeltas-Global Change Program, Paleobiology, NMNH-Smithsonian Institution, Washington, DC 20560,USA bUS Army Engineer Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180,USA |
| Abstract: | Analysis of 92 engineering core logs located in the Balize sector of the eastern Mississippi delta focuses on the late Wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon. This major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin. Observations emphasize lithofacies distributions of the latest Pleistocene sediments underlying the unconformity, the late Pleistocene to early Holocene transgressive facies, and the immediately overlying deltaic deposits. Maps and a cross-section compiled with this information highlight the critical relation between lithofacies distributions and late Wisconsin sea-level oscillations. Core analysis reveals that the transgressive facies comprises distinct environments of deposition, offshore to onshore. Findings identify criteria to determine the approximate position of the shoreline at the late Wisconsin maximum sea-level lowstand and at the extent of early Holocene maximum marine inundation in the Balize complex. Mapping of lithologies along the late Wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high-resolution seismic profiles. An estimate of long-term averaged land subsidence suggests lowering of at least 1 mm/year near the shelfedge during the past  18 000 years. This mapping also refines sea-level response models for the Mississippi delta, including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other Recent marine deltas and in older, stacked deltaic sequences. |
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