ABSTRACT: Simulation of the Response of Carbonate Sequences to Eustatic Sea Level Changes (Tertiary, Northwest Great Bahama Bank): A Scheme for Enhancing Seismic Interpretation

Gregor P. Eberli, Christopher G. St. C. Kendall, Marty Perlmutter, Phil Moore, Robert Cannon, Gautam Biswas, James C. Bezdek

Seismic lines across northwestern Great Bahama Bank (GBB) show prograding sequences with patterns most likely controlled by prevailing currents and sea level. To test this interpretation, computer simulations were made to obtain a visual match between the seismic line and the SEDPAK simulation output. The initial topography, unidirectional wind, and sea level curve defined by Haq et al. were used as fixed inputs, with carbonate accumulation rate and subsidence as variables.

Progradation in a buried, fault-bounded trough (Straits of Andros) began in the middle Oligocene. Simulation produced aggradation from the Late Cretaceous until the middle Oligocene. Afterward, sea level fall shifted the depocenter onto the slopes. Progradation was triggered during the subsequent sea level rise because the upper slope and platform edge remained in the photic zone for an extended period of high carbonate production. This increased rate of sedimentation initiated progradation on the western margin, and on the eastern margin sedimentation was damped by intense wave action.

On the western margin of GBB, where progradation probably began after the middle Miocene, the best simulation was obtained by incorporating a subsiding normal fault block underlying the Straits of Florida. This subsidence from the Late Cretaceous through middle Oligocene kept the deep shelf in the lower photic zone, preventing progradation during the middle Oligocene sea level lowstand. Simulation produced ongoing infilling of the basin that first flattened the margin into a ramp-type geometry over which margin progradation occurred subsequent to the next major sea level drop in the middle Miocene. This is consistent with the time suggested by seismic stratigraphy.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990