ABSTRACT

Sequence stratigraphic analysis of a representative (schematic) dip seismic section along the Louisiana offshore reveals fourth order (Milankovitch) sealevel cycles within third order sequences. This representative line is characteristic of a dip section along the western area where progradation has exceeded subsidence by multifold since the late Miocene from, 6.7 mya, and by two-fold through the rest of the Miocene, back to at least 22 m y a ago. Lowstands cause the outer shelf to act as a sediment bypass zone with shelf deposition during highstands. Salt-sediment interaction is isostatic, the adjustments occurring principally during lowstands.

This interpreted stratigraphy has been simulated on an interactive computer program (SEDPAK) developed at the University of South Carolina. SEDPAK erects models of sedimentary geometries by filling in a two-dimensional basin from both sides with a combination of clastic sediment and/or "in situ" and transported carbonate sediments. Data inputs include the initial basin configuration, local tectonic behavior, sealevel curves, and the amount and source direction of clastic sediment as a function of water depth. The modeled geometries of clastic sediments evolve through "time" and respond to depositional processes that include tectonic movement, eustasy, sedimentation, sediment compaction, and isostatic response, sedimentary bypass, erosion, and deposition in various physiographic settings such as coastal plains, continental shelf, basin slope, and basin floor.

The computer simulation allows for a quantification of the various processes noted and described in the interpretation. Sedimentation rates, isostatic adjustment, and tectonic movement are given in cm/year. Simulation modeling of sequence stratigraphy is seen as the next logical step in the quest for detailed and quantified interpretations.