Quaternary Depositional History of a Shelf-Margin Minibasin, Northern Gulf of Mexico
Conklin, Tucker 1989-
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High-resolution 3D seismic data were used to study the evolution of a shelf- margin minibasin located approximately 160 km off of the coast of Louisiana. Depositional packages were delineated and classified based on observed changes in internal characteristics and lapout patterns. Reconstruction of the depositional history of the minibasin reveals information relating to how depositional styles and architecture change over time in response to eustasy, sediment supply, and salt tectonics. Four shelf-margin deltas were identified and classified into two categories: unstable fluvial-dominated deltas, and stable wave-dominated deltas. Slope failure driven by continued uplift of two salt diapirs bounding the study area on both the eastern and western flanks caused numerous mass-transport complexes to redeposit sediment throughout the minibasin. Slope channels contained within the deltaic packages erode into the underlying substrate, and functioned as a shelf to slope sediment bypass mechanism. Deltaic packages are sometimes capped by muddy transgressive wedges. Prodelta muds and hemipelagic drape deposits also fill portions of the minibasin. A sequence stratigraphic framework was used in order to relate the sediment packages to the sea-level record. Deltaic deposition occurred during lowstand periods, and accounts for the largest packages present in the minibasin. Muddy wedges were sometimes deposited during major transgressions, with high amplitude continuous sediment deposits forming during highstands. Fluvial-dominated deltas show signs of a higher sediment supply and rate, which is indicated by syndepositional internal deformation and greater sediment thicknesses. The wave-dominated deltas present are stable, with no observed deformation. The constraining effects of the minibasin in relation to the depositional styles of the deposits were also examined. In this regard when compared to their open shelf-edge counterparts, the deltas present were more likely to develop shelf to slope bypass systems in the form of slope channel complexes, regardless of wave or fluvial influence.