NEW GEOLOGIC MAP OF BIG BEND NATIONAL PARK, TEXAS: INITIAL EFFORT

Work is underway to produce a modern 1:100K-scale geologic map of Big Bend National Park that upgrades a 1960's-vintage, planimetric-based geologic map. Mapping is planned as a team effort involving geologists from the USGS, universities (Univ. Texas Austin, Permian Basin, and San Antonio; Texas Tech Univ.; Lamar Univ.; Texas Christian Univ.; Sul Ross Univ.; Baylor Univ.; Univ. of Louisiana, Lafayette), state surveys (Texas; Kansas), and the Park itself. The map will be a compilation of published and unpublished modern sources that will be field-checked and modified where necessary and new field mapping that will fill gaps in the modern geologic map coverage. The final map will be digitized in a GIS format, will be plotted on a 1:100K-scale topographic and Landsat 7 base, and will include modern Park boundaries, roads, and trails. Cretaceous through Paleocene sedimentary rocks underlie Eocene through Oligocene alkalic volcanic and plutonic rocks and abundant Neogene bolson and Quaternary surficial deposits. The Park structural setting includes Ouachita-Marathon contractional deformation overprinted by Laramide contraction and by Tertiary Basin-Range style extension. Large areas of the Park underlain by Albian Cretaceous carbonates have been well mapped by Univ. Texas Austin graduate students; these maps have been scanned and incorporated in the new map. Upper Cretaceous and Paleocene sedimentary rocks have either been mapped or are being mapped by academic colleagues. Although pervious investigators mapped the volcanic strata of the Chisos Mountains and plutons within the Park, we recognize that new mapping must concentrate on these igneous areas because their field relations and genesis are not well understood and because large modern mapping gaps exist. Pre- and post-volcanic, basin-fill deposits have been mapped by academic colleagues and are scanned, but will require careful compilation and integration with surrounding areas. Enormous areas of unmapped Quaternary and Pliocene (?) surficial deposits present a serious gap in mapping; these areas will be mapped using aerial photographic interpretation aided by field checking. This team effort will provide an informative map to the public, a resource for park management, and a valuable contribution to the geoscience community.