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Integrated Geological, Geochemical, and Geophysical Studies of Big Bend National Park

National Coooperative Geologic Mapping (NCGM) - Geologic Mapping in Big Bend National Park and Adjacent Areas

Task Contacts: Robert Bohannon, William Page, and Kenzie Turner | Task Objectives | Task Highlights and Key Findings | Task Products

Task Objectives

Photo of Santa Elena Canyon
Stratigraphic studies in Santa Elena Canyon were part of the mapping effort in the park.

Although BBNP, the 8th largest National Park in the contiguous United States, serving about 350,000 visitors each year has world-class complex unique volcanic, structural, geomorphological, surficial and paleontological characteristics, there is no modern map of BBNP or the region. Maxwell and others (1967) synthesized earlier work that is presently outdated. Accordingly, the NPS has ranked BBNP as second nationally in need of a new bedrock and surficial geologic map. Fundamental problems with the lack of geo-referencing and topographic base make the Maxwell and others (1967) map difficult to digitize accurately. Deficiencies include undivided volcanic and surficial deposit stratigraphy, poorly mapped intrusive bodies, and imprecise dating of igneous rocks. Thus, the main objective of this USGS project task is to produce a modern, 1:100,000-scale, digital geologic map in order to address fundamental product needs of BBNP visitors, Park resource management, and academic purposes.

The size of the mapping task was immense, as BBNP covers 3,236 km2 and parts of 31–7.5' quadrangles. Since the Maxwell and others (1967) map was published, high-standing Albian carbonate mesas have been well mapped by academic groups and are being compiled on a Landsat 7/USGS/topographic base. Academic colleagues either have mapped or continue to map much of the lowlands between the mesas, largely underlain by Upper Cretaceous clastic and carbonate strata. High-standing, rugged, and remote Chisos Mountains, underlain by alkalic volcanic strata and two calderas were studied during this project. Large areas of Quaternary and Pliocene surficial deposits were also mapped during this project. Numerous intrusive bodies or extrusive vents were also studied. The northwestern addition to BBNP, including the laccolithic bodies in the Rosillos Mountains, were mapped and compared to new aeromagnetic data. The USGS, in collaboration with partners from the NPS, universities, and state surveys provided a basic geologic framework for BBNP including bedrock and surficial geologic mapping, geophysical, geochronological, and geochemical surveys, and a variety of topical studies. New geologic mapping and compilation of existing geologic maps at 1:100,000 scale by the USGS and academic partners were compiled into the new map of BBNP.

Highlights and Key Findings

Compilation of the geologic map continued into 2008, and the main objective of work focused on final preparation of the BBNP 1:100,000-scale geologic map and accompanying pamphlet. The USGS hosted a Big Bend Technical Session at the 2007 Geological Society of America annual conference in Denver, where the results of many geological, geophysical, and geochemical studies of BBNP were presented.

Geologic mapping was completed in areas of data gaps in the Cerro Castellan and Smoky Creek quadrangles. Checking newly identified edge matching errors and data gaps were completed. Current geologic line work, which is divided into multiple databases, was generalized into an appropriate scale and combined into one comprehensive digital database allowing standardization of attributes.

Surficial mapping in BBNP was completed in the Ernst Valley, Sue Peaks, Stillwell Crossing, Mesa de Anguila, and Lajitas 1:24,000-scale quadrangles. Integration of surficial geologic mapping from other scientists in the Glenn Spring, Solis, San Vicente, and Rio Grande Village quadrangles was compiled into the 1:100,000-scale geologic map.

The USGS worked in collaboration with university mappers and geochronologists in establishing a stratigraphic correlation scheme for the igneous rocks based primarily on trace element whole rock geochemical analyses. The work was helpful in defining the stratigraphic framework and map units of the igneous rocks for the new geologic map of BBNP. Research from this task of the BBNP project resulted in publication of summaries of the regional tectonic history in the Big Bend area and a study of volcanic rocks in the western part of BBNP, which were presented in USGS Circular 1327.

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