Alton Brown, Ph.D.
The transition from Morrowan-Atokan foreland basin (Fort Worth basin) to west- prograding passive margin (Eastern Shelf) deposition is characterized by a complex distribution of Desmoinesian (Strawn) and Missourian (Canyon) carbonate buildups significantly different from the simple west-prograding mixed carbonate-clastic shelf- slope system characteristic of later Eastern Shelf deposition. The complex Strawn and Canyon depositional patterns reflects the influence of three regional controls: tectonics, sediment supply, and sea level. The purpose of this presentation is to present regional and local sediment distribution data that help explain why the simple east to west Eastern shelf progradation pattern was delayed until the end of Canyon deposition.
Well documented regional sediment distribution data indicate that the regional paleogeographic setting was somewhat different than commonly assumed. (1) The Ouachita belt at this time was relatively narrow and not a voluminous sediment source. Most siliciclastics were delivered from southeastern Oklahoma over the Muenster Arch. (2) The western limit of Ft. Worth foreland basin deposition was the Concho platform, not the Bend Arch. (3) Ft. Worth basin differential subsidence stopped during middle Strawn deposition. Later subsidence was regional and increased towards the Red River Uplift.
The middle-late Strawn buildup trend was nucleated on the Concho Platform axis. Backstepping which isolates small lowstand Strawn buildups was predominantly an eustatic sea-level rise, but drowning on the Concho Platform was probably amplified by tectonics. The Strawn buildup trend confined most Strawn siliciclastics to the east. Siliciclastics were transported west of the buildup trend mainly in the north during times of extended low stand. Canyon deposition is characterized by two regional buildup trends, an outer trend nucleated on the older Strawn buildup trend and an inner shelf trend. A shelf basin developed east of the Canyon buildup trend during Palo Pinto deposition and persisted to end of Canyon deposition. The inner shelf buildup trend formed on the southeastern margin of the shelf basin. The shelf basin was filled mainly by siliciclastics prograding from southeast to northwest during Winchell and later Canyon deposition. The Virgilian (Cisco) west-prograding shelf-slope system developed because the shelf was relatively flat (Canyon shelf basin had filled) and siliciclastic sediment supply increased as tectonic reactivation exhumed source areas in southeastern Oklahoma.