76 research outputs found
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Geology of Sierra Del Carmen, West Texas and Mexico: A General Geologic Framework to Support Mapping of Biologic (Botanical) Resources
The purpose of this study is to provide geologic base maps to support the mapping of biological (botanical) resources in the Sierra del Carmen, Coahuila, Mexico, and adjacent areas in Big Bend National Park, Brewster County, Texas. Sierra del Carmen, which generally trends north-northwestward, includes the eastern part of Big Bend National Park and extends southerly into adjacent Coahuila. The range, which is within the Chihuahuan Desert, rises abruptly from the desert floor and has topographic relief that exceeds 2,000 m. The terrain is rugged, and the range is marked by numerous narrow and steep-sided canyons and valleys. The stratigraphic framework of the range is one aspect that controls the distribution of vegetation throughout the area. In general, different rock types can weather into soils of different composition, and the rocks and soils may contain different amounts of moisture. Thus, different plant species may be associated with specific rock lithologies. Geologic structures such as faults, folds, and fracture zones control the position of the rock units and influence landforms, drainage directions, and canyon development. Structures may also influence the concentration and retention of surface moisture. The geologic map of this region is intended to assist other scientists, students, and interested visitors in understanding the geology of this fascinating area and in interpreting the influence of the geologic framework on related sciences. The map emphasizes bedrock and surficial units that can be important controls on the distribution of plant communities.Bureau of Economic Geolog
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Regional Geologic Setting of the Eagle Flat Study Area, Hudspeth County, Texas
The Eagle Flat study area lies near the eastern limit of the Basin and Range geologic province in Trans-Pecos Texas. The geologic features of the region record a long history of geologic events. By describing the regional geologic setting, we can place the Eagle Flat study area within a larger context, and the significance of the site-specific investigations can be more properly understood. In general, the discussions are arranged chronologically, from oldest to youngest; each characterizes the regional geologic framework and describes how the proposed site at Faskin Ranch fits within that geologic setting.
The oldest rocks in the region are metamorphosed Precambrian sedimentary and igneous rocks. Precambrian rocks crop out about 6 miles (9 km) east of the proposed repository site and are extensively exposed in the hills in the northeast part of the study area and in the Carrizo Mountains east of the Eagle Flat study area. Precambrian rocks are also present in isolated occurrences on the northeast flank of the Eagle Mountains, southeast of the site, on the Diablo Plateau, and in the Franklin Mountains, and in New Mexico. In northeastern Chihuahua, Precambrian rocks are present in limited outcrops but are known primarily from deep exploratory drilling. The Precambrian rocks show evidence of sedimentation, magmatism, metamorphism, and deformation before deposition of overlying Paleozoic and younger strata. The greater depth of burial of Precambrian rocks in Chihuahua is interpreted to be partly a manifestation of Precambrian faulting and subsidence associated with a wide northwest-trending zone that parallels the Rio Grande. This zone, the Texas Lineament, broadly trends through the study area and locally coincides with younger geologic structures.Bureau of Economic Geolog
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Summary Report for the 1997-1998 STATEMAP Project: Geological Mapping to Support Improved Data Base Development and Understanding of Critical Aquifers of Texas
This Texas STATEMAP project involves the geologic mapping of areas where improved
geologic information can impact development, land use, public education, environmental
protection, and the economy. The study is divided into two subprojects. Work for subproject 1
deals with the second year of mapping for a three-year mapping study of karst aquifer areas
undergoing rapid urban growth along the Edwards aquifer and recharge zone. Three map areas
are included in subproject 1: West San Antonio, Austin-Georgetown, and Del Rio (fig. 1). These
areas include some of the fastest-growing urban areas in Texas. Development of this area has
been further stimulated by NAFTA because the region is traversed by major transportation routes
from Mexico. Part of the Edwards aquifer is currently the sole-source aquifer of San Antonio.
Geologic maps of subproject 1 areas provide basic information necessary for managing water
and land resources and construction practices.Bureau of Economic Geolog
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Summary Report for the 2001–2002 STATEMAP Project: Geological Mapping to Support Improved Database Development and Understanding of Urban Corridors and Critical Aquifers of Texas
This Texas STATEMAP project involves geologic mapping of areas where improved geologic information can assist development, land use, public education, environmental protection, and the economy. Work during the past year focused on new mapping and digital compilation projects within four study areas (fig. 1): (1) digital compilation (1:100,000) of geology of the northern segment of the Edwards aquifer recharge zone, south-central Texas, Project 1; (2) geologic mapping (1:24,000) of the Hill Country Trinity aquifer recharge zone, south-central Texas, Project 2; (3) geologic mapping (1:24,000) of the San Marcos-Seguin corridor, Project 3; and (4) digital compilation of geology of Quihi and Timber Creek quadrangles-part of the West San Antonio corridor and Edwards aquifer, Addendum Project 4. Geologic maps produced by each of the projects address groundwater resource and urban development issues that are of paramount importance to the affected regions of Texas. Improved geologic maps benefit the management of two major aquifers that are critical to Texas, the Edwards and Hill Country Trinity aquifers, and a minor aquifer, the Leona aquifer. The improved geologic maps of each of the areas produced by this project will aid professionals and the public in making informed decisions regarding land use, aquifer management, and environmental protection for urban-growth corridors in south-central Texas.
Deliverables produced for this 2001-2002 contract year are (1) Project 1: digital 1:100,000-scale open-file map of the northern Edwards aquifer, Geologic Map of the West Half of the Taylor, Texas 30 x 60 minute Quadrangle; (2) Project 2: 12 open-file geologic quadrangle maps (1:24,000) of the Hill Country Trinity aquifer west of Austin and north of San Antonio; (3) Project 3: 2 open-file geologic quadrangle maps (1:24,000) of the San Marcos-Seguin corridor; and (4) Addendum Project 4: draft digital map/GIS database of Quihi and Timber Creek quadrangles, two quadrangles within the West San Antonio corridor and Edwards aquifer, Quihi and Timber Creek quadrangles.Bureau of Economic Geolog
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Summary Report for the 2002-2003 STATEMAP Project: Geological Mapping to Support Improved Database Development and Understanding of Urban Corridors and Critical Aquifers of Texas
This Texas STATEMAP project involves geologic mapping of a portion of the Seymour aquifer of North-Central Texas (Fig. 1). The "Geologic Map of Seymour Aquifer Deposits, Vernon, Texas, 30 x 60 Minute Quadrangle," the deliverable for this 2002-2003 contract year, addresses groundwater-resource issues related to the aquifer. The map and related geologic data are intended for a diverse audience, including geologists, hydrologists, engineers, students, and laypersons. Uses include (a) identifying aquifer recharge boundaries, (b) characterizing attributes and variations within the aquifer strata, and (c) providing information necessary for land-use activities such as locating landfills and other waste-disposal sites. The map and related geologic data can also be used with Seymour aquifer information to analyze the aquifer's groundwater flow and response to pumpage and recharge for future water-management decisions. The aquifer has been an important source of water for irrigation, municipal pumpage, and industrial and livestock use in the area.Bureau of Economic Geolog
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Description and Quaternary History of the Campo Grande Fault of the Hueco Basin, Hudspeth and El Paso Counties, Trans-Pecos Texas
The Hueco Basin of Trans-Pecos Texas and Chihuahua, Mexico, formed in response to Basin and Range extensional tectonism that began about 24 million years ago and continues to the present. The southeastern arm of the basin is asymmetrical with the thickest sediments deposited along the fault-bounded basin axis near the southwestern flank. Approximately 45 km long and striking northwestward, the Campo Grande fault is 12 km from the northeastern basin edge; it divides the downthrown, central part of the basin (>2,000 m of fill) from the shallower (175 m of fill) northeastern flank. Another major northwest-striking fault dips northeastward and bounds the southwestern basin margin in Mexico.
The Campo Grande fault trend is composed of en echelon fault strands that are 1.5 to 10 km long and have strikes of N25° to 75°W. Dips are between 60° and 90° southwest. Displacements decrease near terminations of strands. Grooves on fault planes indicate mostly dip-slip movement. Fault scarps have been modified by erosion of the footwall and deposition on the hanging wall. Erosion-resistant caliche (stages IV to V) at the surface aids in preserving scarp heights of between 1.5 and 11.5 m and scarp slopes of 4° to 17°.
Analysis of faulted upper Tertiary and Quaternary units indicates that successively younger units have less displacement. Maximum vertical offset measured across fault strands cutting the middle Pleistocene Madden Gravel (0.6 to 0.4 million years old), which caps the Camp Rice Formation, is about 10 m. Repeated arroyo incision and fluvial aggradation since the middle Pleistocene have developed Pleistocene terraces that are locally correlative and are mapped as parts of the regionally outcropping Ramey and Balluco Gravels. Holocene terraces also occur. Maximum throws across fault strands that cut Ramey terraces (0.4 to 0.1 million years old?) are 2.5 to 3 m, but some Ramey deposits overlie fault strands and are not faulted. Offset of Balluco (0.1 to 0.025 million years old?) and Holocene terraces has not been observed at fault strands that cut Ramey terraces. The average recurrence interval is 0.1 million years (maximum), and the last faulting episode was late Pleistocene. On the downdropped block of one fault strand, faulted calcic horizons (0.5 to 1.0 m thick; stage III) with vertical separations of 1 to 2 m indicate at least five episodes of movement, deposition, and surface stabilization during the last 0.6 to 0.4 million years. Maximum vertical offset during the last faulting event was about 1 to 1.5 m.Bureau of Economic Geolog
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Mineral Resource Assessment of Lands Administered by the Texas General Land Office in the Franklin Mountains, El Paso County, Texas
The Franklin Mountains, with relief as great as 2,700 feet, bound the west edge of the northwest Hueco Basin. El Paso lies at the southern margin of the mountains where they terminate at the Rio Grande. The mountain range, a west-dipping, tilted fault block that trends northerly, is composed of a relatively continuous stratigraphic section of Precambrian through Permian rocks that are locally intruded by Tertiary igneous rocks (Harbour, 1972; LeMone, 1982, 1988). Quaternary alluvial-fan deposits have built up off the edge of the mountains into the adjacent basins (Raney and Collins, 1994a, b). Tertiary to Quaternary basin-fill fluvial and older lacustrine deposits rarely crop out. We have compiled the geology of the El Paso and North Franklin Mountain quadrangles, which are enclosed in the pocket at the back of this report.Bureau of Economic Geolog
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Summary Report for the New Braunfels, Texas, STATEMAP Project, 1995
Geologic mapping of the 7.5-minute quadrangles that make up the 1:100,000-scale New Braunfels, Texas, sheet (figs. 1 and 2) has continued as scheduled during 1994-1995. Ten quadrangles (Van Raub, Helotes, Waring, Ranger Creek, Jack Mountain, San Geronimo, Comfort, Turkey Knob, Pipe Creek, and Medina Lake) were mapped during this time (fig. 2). During the 1994-1995 contract year, we completed mapping for the 1:100,000-scale New Braunfels, Texas, sheet, an area that contains 32 7.5-minute quadrangles. We anticipate the color 1:100,000-scale geologic map and its text will be published during 1996 as scheduled. This project has succeeded in making useful geologic information for a geologically critical part of Texas available to the public. Thirty-two open-file geologic maps, at 1:24,000 scale, are available, and studies related to the mapping contributed to three published papers (Collins, 1993; Collins, 1994; Collins, in press).Bureau of Economic Geolog
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Late Cenozoic Faults of the Region Surrounding the Eagle Flat Study Area, Northwestern Trans-Pecos Texas
The Eagle Flat study area is located along the southeastern edge of the southern Basin and Range-Rio Grande tectonic province in Trans-Pecos Texas. The desert region that encompasses the study area consists of the broad Diablo Plateau and a series of mountain ranges and adjacent intermontane basins that formed by extensional faulting that probably occurred in the last 24 mya. There has been no historical surface rupturing of faults in Trans-Pecos Texas, although earthquakes have occurred and faults that displace Quaternary (present to approximately 2 mya) deposits are present (fig. 1). Geologic investigations of faults active during the Quaternary provide important data (tables A-1 and A-2) for seismic risk studies of the proposed Eagle Flat low-level radioactive waste repository. Most of the Quaternary faults of Trans-Pecos Texas are between about 11 and 24.8 mi (18 and 40 km) long (table A-1). Many of the faults are sections of longer fault zones that are between 43 and 64 mi (70 and 105 km) long. Strikes of individual faults are variable, although most of the fault zones strike northwestward or northward. Faults dip between 50° and 89°. Fourteen Quaternary faults are within 31 mi (50 km) of the proposed repository.Bureau of Economic Geolog
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Regional Geologic Setting of the Fort HancockStudy Area, Hudspeth County, Texas
The Fort Hancock study area is located within the Basin and Range geologic province in Trans-Pecos Texas. The geologic features of the region record a long history of geologic events. By describing the regional geologic setting, the Fort Hancock study area can be placed within a larger context, and the significance of the site-specific investigations can be more properly understood.
The oldest rocks present in the region are Precambrian crystalline rocks, although none crop out within about 20 mi (32 km) of the proposed repository site. Precambrian rocks are present in the Hueco Mountains to the west and in isolated occurrences on the Diablo Plateau to the north of the study area. In northeastern Chihuahua, Precambrian rocks are known primarily from deep exploratory drilling. The Precambrian rocks show evidence of sedimentation, magmatism, metamorphism, and deformation prior to deposition of overlying Paleozoic strata. The greater depth of burial of Precambrian rocks in Chihuahua is interpreted to be a manifestation of Precambrian faulting and subsidence southwest of a structural zone that parallels the Rio Grande. This structural zone, which projects close to the study area, is also coincident with younger geologic structures and has been termed the Texas Lineament.Bureau of Economic Geolog
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