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Structural Analysis of Strike-slip Faulting in Ernst Tinaja Canyon, Big Bend National Park, TX


Ernst Tinaja canyon in eastern Big Bend National Park cuts through Cuesta Carlotta and exposes locally folded and faulted Cretaceous strata. The Sierra del Carmen Mountains to the east are uplifted, thrusted Laramide monoclines overprinted by Basin and Range extension. To the west are Tertiary volcanics of the Chisos Mountains. To the north are Paleozoic units that were folded and thrust faulted during the Ouachita orogeny. Thus, Ernst Tinaja sits at the nexus of several major structural and volcanic trends in North America. Short-wavelength folds are common in the thin-bedded Boquillas Formation (Eagle Ford equivalent) near the mega-pothole, Ernst Tinaja. Some clay-rich Boquillas layers thicken slightly in fold hinges, but folds are otherwise mostly parallel, open to tight, flexural-slip folds. Orientation of mesoscale thrusts in the Boquillas match flexural-slip directions. Several steep breccia zones cutting the canyon may be a combination of Basin and Range extension and strike-slip faulting. The Boquillas overlies thick-bedded, faulted Buda Limestone. The Buda is also folded but the wavelength is in miles. Upstream (east) of Ernst Tinaja, the canyon makes a 90 degree turn to the north. Numerous horizontal slickensides in the north/south canyon segment indicate significant, previously unmapped strike-slip movement that was apparently primarily sinistral (though there are also indications of dextral movement). A short, sharp bend in the canyon may have resulted in transpressional deformation. Clay cake modeling is in progress to study the geomechanics of the stresses and structures in this area. A goal of this research aims to contribute to our understanding of transpressional related structures and their evolution through multiple tectonic events. This research is applicable to the Petroleum industry by contributing to an understanding of how the Boquillas Formation, the west Texas equivalent of the Eagle Ford Formation, responded to deformational stresses and what kind of structures may be encountered in this unit in the subsurface. This is work is being conducted for a Master's thesis at Stephen F. Austin State University