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BIXLER, WILLIAM G., and JAMES J. WILLIS, Department of Geology; Baylor University Waco, TX

ABSTRACT: Structural Style and Tectonic History of the Arbuckle Mountains, Southern Oklahoma

Construction of U.S. Interstate Highway 35 across the Arbuckle Mountains of southern Oklahoma resulted in a series of roadcuts that provide a nearly continuous "cross section" of the regional structure and stratigraphy. Although these outcrops are frequently used as stops on numerous academic and industry field trips in the Arbuckle region, virtually no work involving the detailed analysis of small-scale structures exposed in these roadcuts has been published. We therefore systematically identified, described, and interpreted these exposed structures, applying additional surface and subsurface observations made elsewhere in the Arbuckle region, in order to determine the overall structural style and tectonic history of the Arbuckle uplift.

Structures exposed in the Arbuckle region record a dynamic deformational history, but are generally consistent with an overall structural style of concentric (or parallel) deformation in response to regional horizontal compression.

Willis (1992) previously classified five types of geologic structures which commonly develop in parallel-folded strata: fore-limb ("rabbit-ear"), back-limb, and cross-crestal structures, pop-out anticlines, and synclinal-hinge faulting. Examples of each of these structures, as well as other characteristics of concentric deformation, including geometric fold habit and multiple detachment levels, were identified in the Interstate 35 roadcuts and elsewhere within the Arbuckle region. These features and additional structures, including bedding-plane and tectonic stylolites, and fractures (both shear and tension gashes), were used to reconstruct the stress/strain history ofthe Arbuckle uplift.

During the late Precambrian to middle Cambrian, the Arbuckle Mountain region was affected by the initial development of the southern Oklahoma aulacogen. Crustal rifting was accompanied by the formation of major marginal normal faults and emplacement of rhyolites, basalts, and hypabyssal intrusions. Rapid sedimentation and subsidence within the aulacogen resulted in the accumulation of thick sedimentary Sequences. As sedimentation andburial continued, numerous bedding-plane stylolites and perpendicular calcite-filled tension gashes formed in response to the increasing vertical overburden stresses. Later plate-tectonic reorganization during the late Paleozoic, however, shifted the maximum principal stress from a vertical to near-horizontal orientation, thereby resulting in regional hori ontal compression which culminated in the closure of the aulacogen system and formation of the Arbuckle-Wichita trend. In the Arbuckle region, uplift occurred primarily in response to basement-involved thrusting along the Washita Valley fault and the blind Arbuckle thrust. Early stages of thrust-related folding were dominated by layer-parallel compression, as indicated by conjugate shear fracture orientations, tectonic stylolites with "teeth" parallel to bedding, and small-scale thrust systems. Bedding-parallel slippage (or flexural slip) is indicated by numerous bedding-parallel slicken lines, and appears to have played an important role throughout all stages of fold development.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.