Fracture Density and Spacing Along Washita Valley Fault, Arbuckle Mountains, Oklahoma

C. D. Ferebee, J. B. Tapp

We document fracture density and spacing associated with the Washita Valley fault, a major strike-slip fault. The Washita Valley fault strikes northwest-southeast with up to 80 mi of exposure in southern Oklahoma and may be an early bounding fault of the Southern Oklahoma aulacogen (Ardmore/Marietta basins). Horizontal displacement on the fault has been estimated to be up to 40 mi, with vertical displacement on the order of 10,000 ft.

Samples collected from traverses across the Washita Valley fault have been analyzed. The traverses cross the fault at different stratigraphic levels from Proterozoic igneous basement, through the Cambrian-Ordovician Arbuckle Group, Ordovician Simpson and Viola Groups, to the Silurian-Devonian Hunton Group. Several types of fracture systems are documented that reflect mechanical stratigraphy, burial depth during deformation, and episodic movement on the fault. The fractures in the study area include open fracture systems, calcite-filled fractures, tension gashes, and fractures related to pressure solution.

The samples were cut parallel to the strike of the fault, vertical-normal to the fault, and horizontal-normal to the fault. These cuts allow examination of the total fracture strain, characterization of the fractures, and statistical analysis of fracture density. From these data, fracture density is shown to decrease exponentially moving away from the primary fault zone.

The increased understanding of fracture patterns and characteristics will assist future exploration and development programs involving carbonate reservoirs associated with strike-slip systems.

AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.