Foraminiferal Biostratigraphy and Paleoenvironments of the Pleistocene Lagniappe Delta and Related Section, Northeastern Gulf of Mexico
Barry Kohl, Richard H. Fillon, Harry H. Roberts, 2004. "Foraminiferal Biostratigraphy and Paleoenvironments of the Pleistocene Lagniappe Delta and Related Section, Northeastern Gulf of Mexico", Late Quaternary Stratigraphic Evolution of the Northern Gulf of Mexico Margin, John B. Anderson, Richard H. Fillon
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The Lagniappe Delta was formed during the Wisconsinan glacial within oxygen isotope stages 2–4. In a study of fossil foraminiferal assemblages from four coreholes penetrating the Lagniappe Delta and related older section, we interpret paleobathymetric zones (inner neritic to upper bathyal) and paleo–water depths within the delta complex. The similarity of fossil assemblages to those of the Recent allows us to use the Mississippi River Delta as a modern analogue. We recognize five of the six modern Mississippi River Delta subenvironments, including fluvial, interdistributary bay, fluvial–marine, deltaic–marine, and sound. A marsh subenvironment was not present.
Calcareous-bank faunas (CBFs) are also abundant in several of the coreholes. CBF foraminiferal taxa, which require warm, clear, shallow water, occur not only in interstadials but also in a prograding clinoform interval in the Main Pass 288 corehole, correlated to the last glacial (isotope stage 2). This apparent paradox is explained by lowered sea level and bathing of the narrow shelf edge by a warm marine current, possibly a proto–Loop Current during parts of the late Pleistocene. The fact that living CBFs do not now occur in modern sediments of the northern Gulf of Mexico supports our thesis that minimum temperatures on the present continental shelf are lower than those of the late Pleistocene–early Holocene. Deep-water occurrences of living CBFs from the northern Gulf of Mexico, cited in published reports, are shown to be relict faunas associated with Pleistocene hardgrounds, calcareous banks, or carbonate pinnacles. The physical parameters controlling the occurrence of living CBFs in the Gulf of Mexico are consistent with those controlling their worldwide distribution.
Foraminifera are used, herein, to recognize unconformities through abrupt vertical changes in the benthic paleoenvironment, sharp variations in temperature-sensitive planktonic species, changes in preservation of benthic foraminiferal tests (non-abraded vs. abraded), and abrupt termination of age-constrained planktonic foraminifera.
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The northern Gulf of Mexico margin encompasses a variety of depositional settings characterized by different drainage basin size, physiography, fluvial morphology, climatic setting, and structural and diapiric activity. This, plus the abundance of long sediment cores and platform borings from oil industry activities, make it an unparalleled natural laboratory for sedimentological and stratigraphic studies and for testing sequence stratigraphic concepts. This volume contains twelve papers describing results from high-resolution stratigraphic studies of late Quaternary strata of the northern Gulf of Mexico, from the mouth of the Apalachicola River to the Rio Grande. These papers focus on fluvial response to climate and base-level change, variations in delta growth and evolution across the shelf, lowstand delta-fan evolution, the evolution of transgressive deposits on the shelf, the preservation of these deposits. The robust chronostratigraphic frameworks developed for the different study areas allows comparison of stratal geometries produced by contemporaneous depositional systems operating under identical eustatic conditions. This volume will appeal to sedimentologists and stratigraphers interested in source to sink issues, such as how various forcing mechanisms influence strata formation on continental margins.