A Late Jurassic Rift, Southeastern Gulf of Mexico

Gyorgy L. Marton, Richard T. Buffler

A detailed analysis of available geophysical and geological data allows us to determine the tectonic setting and geological evolution of the southeastern Gulf of Mexico. In the framework of the Mesozoic opening of the Gulf of Mexico basis, this area played a unique roll. During the Late Jurassic oceanic crust formation in the Gulf of Mexico, the relatively stable Yucatan block rotated about 42 degrees counterclockwise away from Florida around a pivot point in the southeastern Gulf of Mexico (23.46°N, 84.74°W). This block rotation was accommodated by a southward propagating spreading center/rift.

A series of geological cross sections, structure and isopach maps, as well gravity and magnetic anomaly maps in the southeastern Gulf of Mexico are used demonstrate the following main points: a) The continent-ocean transition is well defined by gravity and magnetic anomaly patterns and by topographic changes on the basement structure. b) The oceanic crust becomes narrower towards the south, and at about 24.5° latitude it gives way to a typical continental rift. c) The continental rift northwest from the rotation pole accommodates an increasing amount of northeast-southwest extension. Rifting style gradually changes, as discrete large-scale horst blocks and full-graben features to the south give way to smaller rotated fault blocks and intervening half-grabens to the north. d) Jura sic isopachs reveal rapid variations in sedimentary thicknesses, corresponding to the proposed syn-rift setting. The Jurassic pinches out to the north towards the center of the basin, indicating that oceanic crust formation continued into the earliest Cretaceous. e) Lower Cretaceous isopachs show sedimentation in a typical passive margin basin with a mainly eastern line-source for sediments (Florida carbonate platform). f) Post-mid Cretaceous isopachs show continued fill in the area of oceanic crust, relative sediment starvation in the higher south-central part of the area, and deposition in a narrow foredeep north of the Cuban margin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995