Interpretation of multifold seismic data from the Campeche Escarpment northwest of the Yucatan Peninsula shows geologic features that suggest the sequence of events in the evolution of the Gulf of Mexico. Profiles of the "basement" surface resemble topography typical of subaerial erosion, that is, a pediment surface. An inferred Jurassic salt layer that covers sediments in a downthrown basement block pinches out against the pediment surface. Updip of the salt pinchout and topographically higher are possible Late Jurassic carbonate banks or reefs which onlap the basement erosional surface. A major unconformity separating the carbonate seismic unit from the overlying slope-front-fill unit probably corresponds to a worldwide middle Cretaceous unconformity. Since Late Cretace us, deep-water turbidites emanating from the east coast of Mexico and northern Gulf Coast have dominated the study area.

The scenario revealed at Campeche Escarpment suggests that an early Mesozoic mantle event (plume?) uplifted this once continental area and caused thinning of the crust to near oceanic thickness. Whether and how much of the Gulf of Mexico is underlain by thinned Paleozoic or Mesozoic continental crust, or true oceanic

End_Page 487------------------------------

crust, is still uncertain. The central gulf and interior basins subsided after this period of crustal thinning. It was in these basins that the Sigsbee and Louann Salt were deposited. Later, as the basin margins subsided farther, carbonate sediments onlapped and covered these margins, marking 5 km of subsidence by the Cretaceous. Since the Cretaceous, clastics have infilled the northwestern Gulf, causing an additional 3 km of subsidence of the gulf basin, while the central Florida and Yucatan platforms have stabilized above sea level.

End_of_Article - Last_Page 488------------