Structural style of the Wichita and Arbuckle Orogenies, Southern Oklahoma.

Abstract

Structural style shows significant variation along the mountain front. Two types of variation in style are present. The first is an abrupt variation, occurring where a compartmental fault offsets the mountain front and style shows significant variation across the compartmental fault or across a steep lateral ramp. The second is a gradational variation, occurring as the result of change in fold shape, plunge, gradual variation in elavation of lateral ramps, fault-to-fold interchanges, and progressive loss of slip along strike.

Structural style is of horizontal compression along low-angle basement-involved thrusts. Structural style is determined by magnitude of basement folding during early-stages of deformation. Shortening was accomplished primarily along southwest-dipping thrusts, although significant northeast-dipping back thrusts are present. The major basement-cored uplifts form an en echelon arraignment which trend northwest-southeast, with primary vergence to the northeast. Basment thrusts lose slip laterally, terminating as fault-fold interchanges or against compartmental faults. Two end members of basement deformation exists, though in most areas deformation is a hybrid between end members. Mode I is similar to Berg's (1962) fold-thrust model. Foreland detachment structures, which form large intra-basinal folds, provide strong geometric evidence for syncline crowding and evidence folding prior to the development of the main mountain-flank fault. In mode II, initial folding is relatively minor. Deformation occurs primarily by faulting along a low-angle thrust whose shape may be modified by fault-bend folding. After leaving the basement, the fault typically travels in the Arbuckle Group as a flat or low-angle ramp.

Pennsylvanian deformation in the Southern Oklahoma Foreland occurred as a basement-involved fold belt which resulted in intra-plate crustal shortening foreland of the Ouchita System. Deformation is characterized by northwest trending faults which dip at low- to moderate-angles to the southwest and northeast, is superimosed across a Precambrian-Cambrian grain of extension, and was part of regional Mississippian-Permian intra-plate crustal shortening. Deforamation occurred in two pulses: (1) the Wichita Orogeny, which occurred from Mississippian through Atokan, which uplifted the Amirillo-Wichita Mountains, and (2) the Arbuckle Orogeny, which occurred from Virgilian to early Wolfcampian and uplifted the Arbuckle Anticline. Deformation moved from southwest to northeast as a wave.