TECTONIC EVOLUTION OF GULF COAST BASINS

Abstract

ABSTRACT The Gulf of Mexico formed with the rifting and breakup of Pangaea during Triassic and Early Jurassic time. Its formation and the evolution of its tectonic framework as a passive continental margin can be viewed in terms of the interplay of two factors: (1) stresses operating during the rifting of Pangaea and (2) the inherited tectonic fabric of the rifted passive margin that formed at the divergent plate boundary. Various aspects of continental rifting are examined and evaluated in terms of the stresses operating during the rifting process. A revised model involving double indentation tectonics is proposed to explain the suturing of North and South America and the formation of the Ouachita orogenic belt, which consists of a thrusted allochthonous subduction complex, volcanic arc and forearc basins. It also explains the relationship of this belt to the North America craton, with which it collided. This orogenic belt not only frames the Gulf but forms much of the pre-rift basement of the upper Gulf Coast where segments of the volcanic-magmatic arc terrane, possibly represented in the Sabine and Monroe Uplifts and the Wiggins Arch, are now found in the accreted continental margin and appear to have controlled or at least influenced subsequent Mesozoic rifting. The variable aspects of both these interfacing factors are discussed and their influence on the long and active tectonic and sedimentary history of the Gulf Coast and its basins is evaluated. Also the factors that govern the thermal history of the basin sediments are identified. The Gulf of Mexico is unique among passive margins in that the mechanism which caused uplift, rifting, crustal extension, and drift—with accretion of oceanic crust at a spreading center within the Gulf—aborted and stepped southward into the Caribbean, where it formed that plate. In the Gulf, meanwhile, salt, deposited in basins initially formed and controlled by the two interfacing factors during the early opening, became the dominant tectonic mechanism in controlling subsequent sedimentation and facies distribution. Following deposition of the evaporites, the Gulf began rapid subsidence that resulted in formation of a thick prograding sedimentary wedge of both clastic and carbonate strata around its margin. Its final shaping came with Laramide tectonism that not only rejuvenated hinterland source areas to supply voluminous sediment but transported peninsular Mexico eastward to close the Gulf and form a huge sediment trap in which vast thicknesses of Tertiary to Recent sediment were deposited.