ABSTRACT: Structural Development of McKelligon Canyon, Franklin Mountains, Texas

STACY, JOHN K., and FRANCES E. JULIAN, University of Texas at El Paso, El Paso, TX

McKelligon Canyon is located in the south-central Franklin Mountains of west Texas. The Franklin Mountains are a north-south-trending, tilted fault block mountain range. Most workers who have studied the Franklins agree that range uplift occurred after the Cenomanian. Rio Grande rift extension and Laramide age compression are the most commonly cited mechanisms for range uplift. Recently, McKelligon Canyon was suggested to contain Laramide thrust faults at several locations. This study, however, shows that the canyon's structural pattern is characterized by much extensional faulting. No evidence of thrust faults or other compressional features were found. Steep, northeast-dipping (55-80 degrees) normal faults, which strike N60 degrees W and N10 degrees W, are the primary structures wit in the canyon. These faults are oblique to the general north-south trend of the range and have a maximum vertical offset, as measured by stratigraphic separation, of approximately 650 m. Strain values obtained from oriented limestone samples collected from the field suggest an early Rio Grande rift origin for the structures found in this area. Additionally, paleokarst collapse breccias occur in abundance throughout the study area and are confined to the McKelligon Canyon Formation and the lower 2-3 m of the Scenic Drive Formation. The presence of karsting in the upper part of the Scenic Drive Formation and the overlying Florida Mountains Formation could not be verified in the field. These karst features appear to be randomly distributed as seen on the surface, however, this may be due to preferred differential erosion.

AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)