MISSISSIPPIAN BLACK SHALE IN AN OBLIQUE SLIP MOBILE ZONE: THE CANEY SHALE IN THE ARDMORE BASIN, SOUTHERN OKLAHOMA

The Caney Shale (Visean–Serpukhovian) is part of a belt of basinal black shale units that extends from the Texas Promontory to the Alabama Promontory in the Appalachian-Ouachita foreland. The Ardmore Basin is near the center of this belt and is part of an oblique-slip mobile zone where an Iapetan transform intersects the Ouachita Orogen. The Caney overlies the Tournaisian–Visean Sycamore Limestone and includes phosphatic black shale that is part of the Barnett-Fayetteville-Floyd section overlain by progradational carbonate at the fringe of the Pitkin-Bangor carbonate bank.

The Admore Basin is bounded by and contains giant (>7 km amplitude) oblique-slip fault-propagation folds that strike northwest, are basement-cored, and formed above a mid-crustal detachment. Thin-skinned thrusts also are present, and an arcuate imbricate fan in the Ouachita Orogen marks the southeast end of the basin. Basin modeling demonstrates that the Ardmore Basin has a prolonged structural history tied to Laurentian tectonic events punctuated by rapid, high-magnitude transpression and elevator subsidence associated with reactivation of the Iapetan transform during the intracratonic Wichita and Arbuckle Orogenies.

This research includes the fi­rst modern basin models of the Ardmore Basin and was performed to assess the tectonic evolution and thermal maturation of Devonian-Mississippian black shale. All models show thermal subsidence following Iapetan rifting, shelf stability during the mid Paleozoic, Mississippian-Pennsylvanian synorogenic subsidence, and Permian relaxational subsidence. This was followed by Late Permian–Early Cretaceous uplift and unroofing and Cretaceous–Paleogene subsidence of the Gulf of Mexico Coastal Plain.

The Devonian–Mississippian shale section has a broad range of thermal maturity (R_o = 0.4–2.0%), which is strongly dependent on structural position. Isoreflectance lines are subhorizontal and cross-cut structure, indicating a post-kinematic signature in which strata are immature in uplifts and overmature in the deepest synclines. The post-kinematic pattern is a product of a rapid, early phase of synkinematic maturation that has been obscured by a prolonged period of post-kinematic maturation.