Chapter 8 The Southern Midcontinent, Permian Basin, and Ouachitas

Abstract

Abstract This chapter is concerned with the southern portion of the craton, the southern craton margin, and its geological relationship with the Ouachita Orogeny. The southern continental margin was shaped by extensional and transform faulting, during the breakup of Rodinia, and includes the Oklahoma Basin, a basin formed by transtensional faulting. Carbonate reef systems flourished along the entire continental margin from Texas to Newfoundland during the Early Paleozoic. Shallow-water, carbonate, and siliciclastic sedimentation continued in the Oklahoma Basin from Middle Ordovician through Earliest Mississippian time. The ocean that lay south of the North American Plate through much of the Paleozoic was closed by collision with Gondwana, starting in the Mid-Mississippian. Northwesterly directed contractional stress generated a regionally distinctive style of transpressive fault and block-uplift deformation across the Southwestern United States. Mild warping of the Texas–Oklahoma area during this period accentuated existing differentiation of the continent into a series of basins (including the Delaware and Midland basins) and intervening uplifts (Diablo Platform, Central Basin Platform, Eastern Shelf, Llano Uplift, Ozark Uplift). That portion of this basin and uplift system located within Texas now constitutes the classic Permian Basin. The carbonate platform and basin configuration of the Permian Basin is similar in topography and scale to that of the Cretaceous to modern Bahamas Platform. The basin is probably best known for the distinctive “clinoform” stratigraphy of the Capitan Reef, one of the first places where the lateral facies transition from back reef, through reef crest, foreef slope to basin floor was mapped and described in detail, based on superb outcrops in the Guadalupe Mountains. Sediments of the Absaroka Sequence (Uppermost Mississippian to Lower Jurassic) are widely distributed across the continental interior. For much of the Carboniferous to Permian, the Earth was under the influence of repeated, high frequency glacioeustatic sea-level changes. These caused transgressions and regressions that shifted shorelines and depositional systems back and forth hundreds to thousands of kilometers across low-relief continental interiors. The classic Pennsylvanian cyclothems of the southern US Midcontinent are the most characteristic and well-known products of this process. Crustal loading of the continental margin by colliding Gondwana terranes commencing in the Mid-Pennsylvanian generated typical foreland-type basins which now constitute the Ouachita system, and including such foreland basins as the Forth Worth, Arkoma, and Black Warrior basins. In the Ouachita Mountains of Oklahoma and Arkansas some 3,500 m of structurally disturbed Late Cambrian to Mississippian pre-orogenic strata have been mapped. They consist mainly of shales and sandstones, the latter representing a variety of sediment-gravity flow mechanisms.