LATE PALEOZOIC TECTONIC SETTING OF THE EASTERN SHELF: FROM FAULTED OUACHITA FOREDEEP TO INTRACRATONIC BASIN FLANK WITHIN THE ANCESTRAL ROCKY MOUNTAINS

Although the Eastern Shelf of the West Texas (Permian) Basin has only a few recognized structural elements, it lies within the broad Late Paleozoic framework of the Ancestral Rocky Mountains (ARM), as well as on the fringe of Ouachita orogenic foredeep basins. Both Ouachita and ARM uplifts have shed sediment into the area.

In Early Pennsylvanian time, the area was located on the forebulge of the Fort Worth Basin, a foredeep basin that developed beneath and west of the advancing Ouachita thrust sheets. Early Pennsylvanian strike-slip fault systems also occur in the area, notably the Fort Chadbourne and Matador/Red River systems. Foredeep-related subsidence continued into Late Pennsylvanian time, advancing or broadening westward. Uplift of the Wichita ARM axis to the north probably occurred throughout the Pennsylvanian, as seen on its better-dated northern flank.

Beginning in mid-Pennsylvanian time, the West Texas Basin began to subside as an intracratonic basin with its center near Pecos, Texas; this subsidence continued throughout the Permian, overlapping but outlasting ARM deformation. The Eastern Shelf was tilted westward (forming the Bend Arch as mapped today), and a high-relief carbonate/clastic shelf margin developed that bounded the deep-water Midland Basin from Missourian through Leonardian time. A small amount of additional westward tilting took place in the Mesozoic (probably as rift-flank uplift to Gulf-forming extension), forming the regional sub-Albian truncation evident in surface map patterns.

Hydrocarbon generation and migration were controlled by the successive tectonic regimes. Most Pennsylvanian hydrocarbon reservoirs were probably sourced by updip migration from the Midland Basin either in the late Permian or the early Mesozoic. However, Mississippian source rocks were locally important, with lateral migration from the Fort Worth depocenter and vertical migration along the Red River axis possibly charging significant accumulations.