ADAMS, RICHARD L., Mitchell Energy Corporation, The Woodlands, TX
ABSTRACT: Effects of Inherited of Pre-Jurassic Tectonics on the U.S. Gulf Coast
Extensional and compressional tectonic features from the Canadian shield to the United States Gulf Coast reflect repeated and continued movement of crustal elements along northwest-southeast paths. Resultant rift and thrust features formed perpendicular to that orientation. Cycles of ocean formation (rifting), quiescence, and ocean closure (thrusting) control the structural style and stratigraphic sequences that record the accretion of much of the North American continent onto the Canadian shield.
The Triassic separation of North America from South America resulted in an irregular fragmented arc that now extends from Central America to South Florida. Stranded blocks of continental crust, left behind by the jumping of spreading centers during rifting, control the location of major basins over the attenuated crust between the stranded blocks. The former location of the Yucatan Peninsula is now marked by the salt-dome basins of central Mississippi, southern Louisiana, and southeastern Texas. The attenuated continental crust in this area permitted early, thick evaporite precipitation and thicker than normal sediment deposition. Translation of Mexico westward to its pre-Laramide position allows for a closer prerifting fit between North America and South America.
Postrifting tectonic patterns retain an inherited fabric reflecting the Triassic rifting. Triassic horsts, grabens, and half-grabens localized and delineated later microbasins. The term "microbasin" is herein defined as a limited area of deposition, the boundaries of which reflect, or can be presumed to reflect, buried basement-related faulting.
Mapping of trend offsets indicates that northwest-southeast linear patterns exist and imply the presence within these basins of small-scale strike-slip transform faults that control the lateral position and size of individual microbasins. Mapping these microbasins is essential to understanding exploration play concepts within a geologic province. Many Gulf Coast growth-fault basins at depth are related to basement block faulting, and thus fit this definition of microbasins.
Irregular thicknesses of Louann Salt resulted from salt precipitation on a block-faulted basement. The uneven thickness of salt within individual basement fault blocks (grabens and half-grabens) controlled the spatial distribution and size of the resultant salt domes, pillows, and withdrawal areas. This salt movement is one link between the original basement block faults and the resultant growth-fault basins.
AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.