Abstract

The Fort Worth basin, one of several Late Paleozoic foreland basins formed along the front of the growing and advancing Ouachita fold and overthrust belt, has long been considered a preserved remnant of the Ouachita geosyncline. In terms of plate tectonic concepts, however, its geologic evolution represents the Wilson cycle, with opening and subsequent closing of an ocean.

A complete accounting of the entire geodynamic evolution from passive plate margin to collisional orogen requires detailed knowledge of the inseparably linked processes of sedimentation, volcanism, metamorphism, and mechanics of deformation. Each of these processes interacted as the area passed through the various stages of its evolution.

The reconstruction of the tectono-sedimentary history of the Fort Worth basin begins with part of a rifted and retreating plate margin over which Early Paleozoic seas advanced to deposit the shelf carbonates of Cambro-Ordovician age in Texas. Thicker sequences of this same facies accumulated in West Texas and Oklahoma in the more rapidly subsiding Delaware and Wichita aulacogens. During the Middle Paleozoic, a period of tectonic unrest resulted in erosion or non-deposition of sediments in this time interval in the Fort Worth basin area.

The Ouachita facies sediments were deposited synchronously with the shelf carbonate facies. With the closure of a marginal sea, the Ouachita fold-thrust belt evolved as the subduction complex composed of the Ouachita facies strata scraped from the subducting oceanic crust.

By Mississippian time, the continental margin was nearing the subduction zone. The subduction complex grew and was thrust over the continental margin and thus became the major source not only for the early synorogenic flysch sequence of Mississippian-Pennsylvanian age but also the later molasse sequence represented by the Atoka and Strawn deposits. As plate convergence continued, the outer arch or rise flexed the subducting craton. The resultant basinal hingeline controlled sediment facies distribution as it retreated cratonward in response to continued cratonic flexing, as the continental margin entered the subduction zone and Pangaea formed.

With the rifting and breakup of Pangaea in the Triassic, and the formation of the Gulf of Mexico, the southern margin of North America once again became a trailing and subsiding plate margin over which Early Cretaceous seas advanced to deposit the Comanche Series that today overlie the tilted and eroded Paleozoic sequence of the Fort Worth basin.