Paper No. 11
Presentation Time: 11:30 AM
GEOLOGIC MAP OF BIG BEND NATIONAL PARK, TEXAS: A NEW DIGITAL GEOLOGIC MAP
Big Bend National Park is geologically diverse, and tectonic events such as the Marathon and Laramide orogenies, basin-and-range extension, and volcanism and plutonism have produced much of the spectacular topographic expression within the park. This geologic diversity showcased in the park is linked to the extraordinary modern-day biodiversity within the expansive, protected Chihuahuan desert. This new digital geologic map provides Big Bend managers with comprehensive digital geologic coverage of the park, which is critical for natural resource and ecosystem management. New mapping from the U.S. Geological Survey, university professors and students, and the Texas Bureau of Economic Geology includes areas of the High Chisos Mountains, the more recently acquired (1987) Harte Ranch section in the northern part of the park, and revised park-wide mapping of Cretaceous to Eocene carbonate and clastic sedimentary rocks. Mapping of Upper Cretaceous to Paleogene sedimentary rocks identified a more restricted distribution of the Aguja and Javelina Formations and greatly expands the distribution of the Black Peaks Formation. These units document an important transition from marine to continental sedimentation preceding, and overlapping with, the Laramide orogeny, and provide a diverse suite of fossils including dinosaur, giant crocodile, and sea turtle, among others, that were used to decipher depositional environments and to correlate units across the park. Extensive new geochronology and geochemistry contributed to significant revisions in the volcanic stratigraphy, and temporal relationships of intrusive bodies throughout the park were better defined. New mapping of surficial deposits throughout the entire park resulted in characterizing periods of erosion, down-cutting, and aggradation related to integration of Big Bend basins with the Rio Grande. Long-term degradation periodically interrupted by episodes of aggradation up to modern times are recorded in multiple levels of gravel-capping pediments and terraces throughout the park. Extensive erosion in Big Bend during the Quaternary contributed to destabilization of bedrock slopes resulting in the development of large, multi-event landslides.