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Abrupt Climate Change Superimposed on Long-Term Tectonic Control on Paleogene Gulf of Mexico Depositional Systems


We evaluate new and published stratigraphic, geochronologic, mineralogical, and geochemical analysis of the Wilcox Group in the U.S. Gulf Coast to evaluate the controls on the long-term (i.e., 106-107 yr) trend of decreasing Paleocene-Eocene sediment supply to the Gulf of Mexico based on shelf-to-deep-water stratigraphic correlations and sediment-supply modeling (i.e., BQART). Net sandstone maps show the depocenter shifted from east to west and the sandstone-rich fluvial Carrizo Formation (time equivalent to the Upper Wilcox Group) abruptly prograded over the mudstone-rich distal-marine Sabinetown Formation (time equivalent to the youngest Middle Wilcox Group) across the Paleocene-Eocene boundary. Geochronology data from hinterland Laramide basins and the Gulf Coast indicate a decreasing catchment size and increasing lag time between U-Pb crystallization age and depositional age. The enrichment of 1.3-1.8 Ga zircons (Southwest Laurentia) in upstream Laramide basins confirms the previous observation that basement-derived clasts became abundant during the Eocene, possibly as a result of the exposure of basement-cored Laramide uplifts. These tectonic influences contributed to the long-term decreasing sediment supply trend of the Wilcox Group in spite of the increasing intensity of chemical weathering following rising global temperatures across the Paleocene-Eocene boundary. A further examination of eustatic curves and subsidence analysis indicates no strong linkage between the presence of either canyons or deep-water fans and sea-level change. We thereby suggest that long-term sedimentary records of the Wilcox Group of the U.S. Gulf Coast are primarily controlled by upstream tectonic activity. However, climatic events (e.g., hyperthermals) may have abruptly, but temporarily, modified downstream stratigraphy (e.g., depocenter and facies shift) without affecting the long-term sediment budget. The potential link between the sand-rich Carrizo Formation and the Paleocene-Eocene Thermal Maximum may be one such example. We speculate that tectonism may exert the dominant control on long-term sediment supply to the shelf margin in high-relief, continental-scale sediment-routing systems.