Seismic Stratigraphy and Geologic History of Middle Jurassic Through Lower Cretaceous Rocks, Deep Eastern Gulf of Mexico

ABSTRACT A recent seismic stratigraphic investigation in the deep eastern Gulf of Mexico has resulted in the definition of eleven late Middle Jurassic through Lower Cretaceous sequences in the west Florida basin and on the adjacent west Florida slope. The age control is based on tentative correlations with nearby, better controlled study areas. This investigation has produced a general reconstruction of the regions' paleogeography and geologic history. Earliest Upper Jurassic (Oxfordian?) sediments were deposited in a gently sloping ramp-type setting, which evolved into more steeply dipping ramp-type settings during the Kimmeridgian(?) and Tithonian(?). These Upper Jurassic sequences were deposited as broad lobes overlying a (Callovian?) salt sequence. Differential subsidence across a Tectonic Hinge Zone (THZ) toward the end of the Jurassic possibly controlled the establishment of a shallow water rimmed carbonate platform margin at the present day Florida escarpment. Lower Cretaceous deposits are interpreted as aggradational back-reef platform sediments landward of the margin, while coeval deposits in the adjacent basin are interpreted as proximal slope talus, distal slope deposits and overlapping basin floor fans. The lobe geometries of the basin sediments and the presence of a low velocity channel fill on the adjacent Lower Cretaceous platform suggest the possible bypass of siliciclastic sediments across the platform during lowstands and their deposition as deep sea fans in the basin. This also suggests the presence of siliciclastic reservoir rocks in the basin, and could be analogous to the Permian Basin area in west Texas. During the Lower Cretaceous, the platform margin aggraded and steepened, which caused deep sea current systems to become intensified and focused along the margins' base. This intensification was responsible for altering depositional patterns and processes. For example, the earliest Cretaceous fan deposits were generally oriented perpendicular to the basin. With time, the lobes became oriented more parallel to the basin, culminating in the deposition of a large north-south prograding mound. Near the end of the Lower Cretaceous, extremely intense currents, probably due to sea level drops, preferentially eroded these depositional lobes and mounds, culminating in the Mid-Cretaceous sequence boundary (MCSB).