The Appalachian-Ouachita orogen beneath the Gulf Coastal Plain between the outcrops in the Appalachian and Ouachita Mountains

Abstract

Late Paleozoic orogenic structures exposed in the Appalachian Mountains of Alabama and in the Ouachita Mountains of Arkansas extend from opposite directions beneath a cover of post-orogenic Mesozoic-Cenozoic strata in the Mississippi Embayment of the Gulf Coastal Plain (Fig. 1; Plates 6, 9). Although the physiographic expressions of the Appalachian and Ouachita Mountains end at the edge of the Coastal Plain, the orogenic belt neither ends nor changes abruptly along strike at the present onlap limit of Coastal Plain strata. Instead, as shown by data from deep wells and geophysical surveys, a continuous belt of Paleozoic orogenic structures extends beneath the post-orogenic Coastal Plain cover (Fig. 1; Plates 6, 9). Nevertheless, both the Paleozoic stratigraphic sequence and details of structural style exposed in the Ouachita Mountains contrast strongly with those in the nearest Appalachian outcrops, and projection of structural strike from the outcrops does not lead to a simple connection of structures beneath the Coastal Plain cover. Includes 14 chapters on the Appalachian orogen, 15 of the Ouachita orogen, and a chapter on the connection between them beneath the eastern Gulf Coastal Plain. The Appalachian chapters synthesize the geologic development of the orogen by tectonostratigraphic intervals (pre-orogenic, Taconic, Acadian, Alleghanian, and post-Alleghanian), and also treat Paleozoic paleontologic control, regional geophysics, thermal history of the crystalline terranes, parts of the orogen buried beneath the Atlantic and eastern Gulf coastal plains, regional geomorphology, mineral and energy resources; an integration chapter also is included. The Ouachita chapters cover physical stratigraphy and biostratigraphy of the Paleozoic rocks, structural geology, a synthesis of the subsurface geology beneath the western Gulf Coastal Plain, a review of the mineral and energy resources, regional geophysics, and a tectonic synthesis. Twelve excellent plates provide four-color geologic maps, structural cross sections, tectonic syntheses, and geophysical maps; a black-and-white synthesis of Appalachian mineral deposits, and a reflection seismic cross section.