Effects of Inherited Pre-Jurassic Tectonics on Gulf Coast

Richard L. Adams

Extensional and compressional tectonic features from the Canadian shield to the 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 opening (rifting), quiescence, and ocean closure (thrusting) controlled the structural style and stratigraphic sequences that recorded the accretion of much of the North American craton 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 southern Florida. Stranded blocks of continental crust, left behind when spreading centers jumped during rifting, control the location of major basins over the attenuated crust between the blocks. The former location of the Yucatan Peninsula is now marked by the salt dome basins of central Mississippi, southern Louisiana, and southeastern Texas.

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 a limited area of deposition whose boundaries reflect, or can be presumed to reflect, buried basement-related faulting.

Mapped trend offsets follow northwest-southeast linear patterns and imply the presence within these basins of small-scale strike-slip transform faults that control the lateral position and size of individual microbasins. Many Gulf Coast growth-fault basins are at depth implied to be 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.

The double helix concept provides a driving force to explain the recurrence of these northwest-southeast movements along the Gulf Coast and their cyclic nature in an expanding and contracting earth.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.