STRATIGRAPHIC FAULT INDUCTION, APPLICATIONS TO ROTATIONAL BLOCKS IN LISTRIC FAULT SYSTEMS, SIERRA DIABLO BOUNDING FAULT SYSTEM, VAN HORN, TX

The Sierra Diablo is located at the eastern edge of the Basin and Range Province. Development of the Sierra Diablo escarpment is the result of at least 2000 feet of displacement along a normal fault dominated imbricate fault system. The arid climate has preserved outcrop of both shales and carbonates in stratigraphic position and original thickness. Arroyo development has cut through the bounding fault system, enabling study of the fault system in three dimensions.

The outcrop studied in this research shows the rotational nature of fault blocks when an incompetent layer arrests fault development. A paleosol arrested normal fault propagation and initiated listric fault development. With the removal of side load due to the slivered nature of the imbricate fault system, down slope movement of the overlying competent layers resulted in shear between beds and rotation of the entire overlying unit with no apparent effect on bedding below the incompetent layer.

In one of the larger arroyos, an intermediate fault block is exposed that contains a 300 foot section of 2-8 foot thick beds of Permian fusulinid limestone with a south strike and dips ranging from 45 deg. distally to 90 deg. proximal to the Sierra Diablo Horst. This steeply dipping limestone is stratigraphically above a 35-40 foot thick clay-rich paleosol. This paleosol separates the Permian limestone above from a Pennsylvanian basinal limestone with an east strike and dip of 3-5 deg. Local strike and dip of non-faulted Permian carbonates is nearly horizontal, with clinoform architecture causing an apparent easterly dip.

The outcrop was mapped using a laser rangefinder and was verified with measurements of strike, dip, bed length, and analyzed for evidence of extensional/compressional features within beds. Data was used to create a 3-D model for the initiation and development of rotational features in imbricate fault systems.

This model is applicable to fault development in the Canyonlands of Utah and the Corsair Fault of the Texas Gulf Coast. These fault systems developed due to extensional processes and the architecture is defined by the presence of incompetent layer shear and fault propagation arrest. Understanding these processes is important for understanding geologic hazards and reservoir partitioning.