ABSTRACT

Sophisticated computer-based models are available to recapitulate sequences found along a cross-section. Here, results from paleotectonic restoration and simulation modeling have been obtained for a dip seismic section along the western Louisiana offshore. The section contains fourth order (Milankovitch) sea level cycles within Exxon/Vail third order cycles. Propagation has exceeded subsidence multifold in the past 6.7 Ma and by two-fold back to at least 22 Ma. Low stands were times of sediment bypass along the outer shelf with shelf deposition during high stands. Salt-sediment interaction has been isostatic, the adjustments occurring principally during low stands. Paleotectonic restoration modeling is a restoration procedure which utilizes dated reflectors with which to derive sequences. These sequences are back-stripped through time with the remaining sequences geometrically adjusted to reflect original deposition by retaining the cross-section area of each sequence. The result is a series of cross-sections representing geology at times of the various dated horizons. The modeling mechanics are the dynamics of regional tectonics applied to the measured sequences. Simulated stratigraphy is inverse modeling, operated on an interactive computer program (SEDPAK), which constructs models of sedimentary geometries by infilling a two-dimensional basin from both sides with clastic and/or carbonate sediments. Data inputs include initial basin configuration, local tectonics, sea level curves, and amount and source of sediment as a function of water depth.

Both modelings allow for a quantification of the various geologic processes interpreted. These modeling procedures are over different time spans and are complimentary. A paleotectonic restored section, for example, yields an initial basin configuration for subsequent simulation modeling.