Alton A. Brown, "Regional Controls on Pennsylvanian Fort Worth Basin and Eastern Shelf Deposition"

The Desmoinesian transition from the foreland Fort Worth Basin (FWB) to the passive margin Eastern Shelf (ES) was first recognized by Cheney over 70 years ago. Since then, industry and academic studies have deepened our understanding of tectonics responsible for this change as well as the tectonic and eustatic controls on sediment sources during FWB-ES sedimentation. This is an overview of these data and an interpretation of large-scale tectonic, eustatic, and sediment supply controls on sedimentation.

Maximum FWB subsidence rate shifted from west of the Muenster arch (Mississippian) to west of the Ouachita tectonic belt (Morrow-Early Desmoinesian) as growth rates of these structures changed. Foreland subsidence patterns terminated in early Desmoinesian, marking the end of the FWB deposition. Subsidence patterns indicate FWB origin by intraplate stress rather than with foreland loading.

Relatively high Late Desmoinesian – Canyon subsidence south of the Red River Uplift created a shelf basin (Knox-Baylor Trough) separated from the Midland Basin by carbonate banks nucleated on the FWB forebulge (Concho Platform). The northwest end of the shelf basin remained open to the Midland Basin and provided the major pathway for Late Strawn and Canyon sediment transport to the deep Midland Basin. The basin was filled mainly by NW-prograding Missourian carbonates and clastics. The east-to-west progradation pattern characteristic of Virgilian and Wolfcampian ES deposition initiated after filling of the shelf basin.

Eustatic sea level and marine circulation controlled depositional environment distribution and architecture. Termination of FWB deposition is approximately synchronous with onset of high-frequency, high-amplitude, eustatic sea-level changes. Relative sea-level variations created much of the Strawn-Canyon lithostratigraphic complexity. A major marine current system connected the Midcontinent Sea to the open ocean through the easter Midland Basin during most Late Strawn to Cisco deposition. This current helped maintain Midland starved-basin deposition, growth of heterotrophic carbonates on the Strawn-Canyon outer bank system, and growth of the Horseshoe Atoll. Late Virgilian closure of the Amarillo Uplift – Bravo Dome gap in the north and narrowing of the Hovey Channel reduced this circulation, changed Midland Basin carbonate ecology and possibly contributed to drowning of the Horseshoe Atoll.

Most sediment supplied to the FWB and ES was delivered over the southern Muenster Arch. Most sediment shed south from the Wichita Uplift was trapped north of the Red River High in the Hollis basin. The Ouachita tectonic belt was not a major Missourian-Virgilian sediment source because it is a narrow feature that was probably never a major mountain range near the FWB. The Sabine Terrane was not a direct sediment source because it was a Desmoinesian to Wolfcampian marine sedimentary basin. Detrital zircons indicate ES sandstones have Coahuilan Neoproterozoic and Laurentian Mesoproterozoic sources. This is most consistent with sediment reworked during exhumation of the Ouachita Uplift and Arkoma Basin. Sediment supply rate increase during Virgilian due to tectonic reactivation in southern Oklahoma.