Biostratigraphy of a Pleistocene Shelf-Edge Delta System, Northeastern Gulf of Mexico: Recognition of Delta Subenvironments
Barry Kohl, Richard H. Fillon, Harry H. Roberts, 2013. "Biostratigraphy of a Pleistocene Shelf-Edge Delta System, Northeastern Gulf of Mexico: Recognition of Delta Subenvironments", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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The Lagniappe Delta complex formed on the Mississippi/Alabama continental shelf during the Wisconsinan glacial stage, within oxygen isotope stages 2-4. Data collected from four coreholes (Main Pass 242c1, 288c1, 303c1; and Viosca Knoll 774c1), which penetrate the Lagniappe Delta complex and older section provide the basis for our research. In our study of fossil foraminiferal assemblages from these coreholes we interpret paleobathymetric zones (inner neritic to upper bathyal) and paleo-water depths as well as subenvironments within the delta complex. The similarity of Pleistocene-Holocene fossil assemblages to those of the Recent allows us to use the Mississippi River Delta as a modern analogue. Five of the six modern Mississippi River Delta subenvironments are recognizable in the subsurface: fluvial, interdistributary bay, fluvial-marine, deltaic-marine, and sound. A marsh subenvironment is not present in our data set.
An occurrence of warm, carbonate-bank microfauna in a cold, glacial interval in Main Pass 288 is a paradox explained by the close proximity of this site to the paleo-shelf edge during isotope stage 2 and the influence of a proto-loop current.
Based on a reconstruction of the paleoenvironments, paleogeographic maps were drawn at three time slices: 83 Ka (stage 5a/5b boundary); 24 Ka (stage 2/3 boundary); and 19 Ka (late stage 2). These maps show the basinward migration of the shoreline during sea-level fall and the progradation of accreting lobes of the Lagniappe delta during the late Wisconsinan glacial stage.