ABSTRACT

Inferences of paleoenvironment of sediment deposition and salt location in various interrelated types across the dynamic Mississippi Embayment--Gulf of Mexico basin are of paramount importance to petroleum exploration. Paleotectonic restorations have been published for north Louisiana, the south Arkansas basin, and offshore western Louisiana. A published schematic dip depth section from the Ouachita orogen to Yucatan has been restored, aiding regional visualization and quantification of Louann Salt migration and delineation of paleoenvironments.

Along the Louisiana slope, closely spaced dip bathymetric profiles at 5-mi spacing reveal a series of east-west-oriented seafloor highs. These highs are known to be underlain by salt at some depth. The highs are continuous across the data set, some 100+ mi. An interpretation is that the Louisiana slope, from shelf break to Sigsbee Escarpment, is subdivided into generally continuous lenticular strike-oriented intraslope basins. The uniformity of salt-ridge distribution requires an orderly evolutionary mechanism. Whatever detailed salt migration models are applied, salt migration along paleoslope may have been orderly. Although there is general bathymetric conformity across the Louisiana slope and an implied single originating mechanism, there is heterogeneity of seismic stratigraphy and paleophysiography of the outer shelffupper slope of the east and west Louisiana offshore (Mississippi Canyon contrasted with the Garden Banks/Green Canyon). In the Mississippi Canyon area, the shelf break retreated 6 mi from 10.0 to 8.2 Ma, then advanced 55 mi from 8.2 to 2.8 Ma, followed by a retreat of 30 mi from 2.8 to 0.7 Ma. Since then, the shelf break has advanced 20 mi. The west Louisiana shelf break prograded 100 mi during the last 6.7 Ma. These oscillations are dated from paleontological determinations. Representative seismic sections have been simulated to verify calculated geologic inputs.

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