Pennsylvanian Foreland Deformation of Wichita Uplift, Southwest Oklahoma
Pennsylvanian foreland deformation associated with the Ouachita orogene reactivated a west-northwest-east-southeast Cambrian basement trend, the southern Oklahoma aulacogen, to form the Wichita uplift, southwest Oklahoma. The 30-km-wide subsurface Frontal fault zone separates the uplift from the Anadarko basin to the north. Horizontal shortening across this fault zone is estimated at 7-15 km (20-40%), vertical displacement totals 9-10 km from the uplift to the basin.
Under the assumed deformation conditions (effective pressure 50 MPa, strain rate 10-15 sec-1, temperature 100°C), the basement rocks were brittle and rigid. Shortening of the basement occurred along moderate angle (30°-60°) reverse faults with no apparent folding of the upper basement surface. The overlying Paleozoic sedimentary rocks were represented by (1) a well-bedded, 3,500-m Cambrian-Devonian dominantly carbonate section, (2) a 1,250-m Silurian-Mississippian clastic section. Strain was accommodated within these rocks by displacement along the basement reverse faults (mountain flank thrusts) and by northeast-verging asymmetric folds with planar limbs and moderate-tight hinges. These folds are mapped on an interformational scale within the Fron al fault zone, and on an intraformational scale (Cambro-Ordovician Arbuckle Group) in the Slick Hills, southwest Oklahoma. Additional shortening occurred along southwest dipping mountain flank thrusts and on bedding plane thrusts, respectively.
Hanging wall blocks of major faults contain the shallow dipping limb and anticlinal hinge zone of the interformational scale folds. Oil and gas production is generally restricted to these anticlinal crests within Paleozoic rocks. Deep wells (> 6,000 m) that have penetrated footwall imbricates of the mountain flank thrusts have drilled through steep-overturned beds and tight recumbent folds before passing through faults into a normal stratigraphic sequence. Basement thrust loading of the southern margin of the Anadarko basin controlled the trend (west-northwest-east-southeast) of the axis of maximum deposition within the basin during the Pennsylvanian.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.