22 research outputs found
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Future Climatic and Envirornmental Conditions in the Texas Panhandle- A Geological Perspective
Among the many factors to be considered in planning a high-level nuclear waste repository in northwestern Texas are future climatic conditions and their role in affecting environmental change. In future millennia, the regional climate will almost certainly undergo episodic variations comparable to those inferred from the paleoclimatic record of the late Quaternary Period. In addition, local and perhaps global weather patterns may change in ways not previously sustained, as a consequence of inadvertent and possibly deliberate human activities. If the scope and duration of these natural and induced climatic changes were significant, they would appreciably influence geomorphic and geohydrologic processes in the Texas Panhandle.Bureau of Economic Geolog
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Environmental geology of abandoned lignitic- and bituminous-coal mines of Texas
Lignitic, canneloid, and bituminous coals have been mined in Texas since at least the early 1800's and possibly the 1750's. Inactive mining districts are located in most regions of the state and mining continues in several areas. The mined seams of coal lie within sedimentary sequences of the Upper Pennsylvanian, Upper Cretaceous, and lower and middle Eocene Series. Most of the production before 1924 was from underground mines, whereas all coal extracted since the late 1940's has come from surficial mines. Prior to the 1970's, few mines were reclaimed. Consequently, many sites of abandoned coal mines in the state exhibit a wide range of adverse, environmental-geologic conditions, varying both in type and intensity. Conditions at these sites include: subsidence and faulting; effects of combustion; production of toxic, geochemical leachates; erosion, sedimentation, and effects on drainage; and the presence of open mine shafts, structural and mechanical debris, large spoil mounds, and miscellaneous refuse. Quantitative assessments of these conditions at selected sites were qualitatively extrapolated to other areas to permit evaluation of conditions statewide. Some of the most severely affected sites have been reclaimed under the regulatory authority of the Railroad Commission of Texas and by the U.S. Soil Conservation Service. Of the more than 260 sites of abandoned coal mines in Texas perhaps one-fourth eventually may require some corrective attention.Geological Science
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Stratigraphy of a Playa-Lake Deposit Within the Proposed Alignment of the Amarillo-Area Superconducting Super Collider
A limited investigation of playa-lake stratigraphy was conducted at a small unnamed playa approximately one mile northeast of Nazareth, Castro County, Texas (figs. 1, 2). This work was done in support of a study of the proposed Amarillo-area site for the Superconducting Super Collider (SSC) and is intended to complement discussion of the areal geology of the Amarillo-area site by Raney and others (1987).
Three shallow boreholes (B6, B6A, and B6B) were drilled in the northeastern quadrant of the playa (fig. 1 inset). Borehole B6 was drilled near the center of the playa basin, B6A approximately half the playa radius to the northeast, and B6B farther northeast, just outside the playa margin. The three boreholes are aligned along a directional azimuth of N68E. Core was collected from each of the boreholes using Shelby tubes. The depth of all three was approximately 70 ft. The playa contained standing water at the time of coring; equipment access was afforded by a narrow levee road constructed across the playa floor. Boreholes B6 and B6A were drilled through the road fill.
Playa deposits are among the most common late Cenozoic stratigraphic units in the Southern High Plains (fig. 2). The number of playas in the Southern and Central High Plains of Texas may exceed 37,000 (Schwiesow, 1965). Several playas are located near the proposed alignment of the Amarillo-area SSC (fig. 2). Despite their large collective areal extent and a long history of scientific interest in playas in general, the age and origin of deposits filling playa basins in this region remain highly controversial (see brief discussion by Raney and others, 1987).
Playas are ephemeral lakes; their deposits typically include a mix of lacustrine and eolian sediments. Lacustrine silty clay and eolian fine sandy silt deposits of varying thickness are found in playas throughout the study area. Although the composition of playa deposits has been reasonably well characterized, the mechanisms by which their associated basins form and are maintained are not fully understood. At many sites, modern playa basins are inset into older lacustrine deposits, indicating possible genetic cyclicity. A variety of mechanisms may be involved in creating and maintaining playas as a group, and many individual playas may be polygenetic.Bureau of Economic Geolog
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Obtaining Practical Information on the Geology of Texas
Information, like gold, is where you find it. Geological information is no exception, but in Texas such data are often readily at hand. The state has one of the highest concentrations of practicing geologists per capita in the United States; and Texans in general are very conscious of the importance of fossil fuels, earth materials, and land and water resources in the state's economy, history, and quality of life. But where does one turn for specific geological information?
Fortunately, there are many sources of information on the geology of Texas, including:
1) State agencies
2) Federal agencies
3) Colleges and universities
4) Geological (and related) societies
5) Museums and nature centers
6) Oil, mining, and consulting companies
7) Public schools
8) Public libraries
These organizations can often provide published information, films, lectures, and professional advice to persons requiring particular information as well as those who simply have a sincere interest in the geosciences. Most of the state and federal agencies, colleges and universities, and geological societies that engage in studies of the geology of Texas are listed in the accompanying appendices (A, B, C, and D), along with their addresses, telephone numbers, and summary statements of their areas of involvement or expertise.Bureau of Economic Geolog
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Modern Eolian Processes on the Southern High Plains
Eolian processes have substantially modified the landscape on the Southern High Plains within historic times. The maximum inferred rate of deflation was 18.9 mm/year at a site in Bailey County, Texas, a region of loose, sandy soils and frequent, seasonal dust storms. At least locally, agricultural practices have accelerated natural rates of erosion and deposition by winds. An extensive cover of windblown sand and silt mantles the gently sloping surface of the Southern High Plains. Eolian deflation and deposition are among the dominant geomorphic processes affecting this region throughout most of the Holocene and Pleistocene time. Historically, human activities have heightened the importance of wind action by disrupting the natural vegetative cover, thereby exposing the unconsolidated sediments.
Agriculture, particularly dry-land cultivation, has been the principal form of land use in the area since the early 1900s or before (Webb, 1931). The effects of tilling practices on deflation are shown in Figure 1. The cultivated field on the right (east) is approximately 0.8 m lower than the range site on the left (west). This long, narrow field was cleared and probably brought into cultivation in the 1920s (C. D. Tunnell, personal communication, 1983). Its furrows run from north to south, along the field's long axis. The orientation of these furrows tends to maximize local deflation, as the furrows are parallel to the dominant winds. During the winter and early spring, some of the strongest winds are from the north, whereas the prevailing wind direction is southerly at other times of the year (Bomar, 1983). Other factors that enhance the erosional impact of the wind include antecedent dry conditions and frost heaving. Both are seasonal effects that increase the soil's susceptibility to removal during the frequent spring dust storms. After becoming entrained, soil aggregates from this field and others like it are transported from their source and redeposited as a broad sheet of eolian sediment.Bureau of Economic Geolog
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Quaternary Faulting in Southeastern Briscoe County, Texas
Downwarped and penecontemporaneously faulted beds of late Quaternary terrigenous sediment are well exposed in southeastern Briscoe County, Texas. Deformation probably was caused by subsidence of the Permian subcrop owing to dissolution of bedded salt at depth. Fluvial sands and gravels and lacustrine clays fill a subsidence basin, producing a locally thickened Quaternary section. A well-developed paleosol above lacustrine deposits was tilted and laterally truncated prior to modern eolian deposition at the site.
Active, recently active, and inactive subsidence features are common in the western Rolling Plains of Texas. Most of these features are small, karstic sinkholes up to 330 ft (100 m) in diameter and subsidence basins a few miles long. Gustavson and others (1982) investigated more than 400 of these features (dolines) in Hall and Briscoe Counties, Texas. These structures formed and are forming as a result of dissolution of Upper Permian (Ochoan and Guadalupian) evaporites, particularly halite, at depths of 650 to 1,000 ft (200 to 300 m) (Gustavson and others, 1982; McGookey and others, in press).
A similar pattern of karstic subsidence produced features of comparable size throughout late Pleistocene and Holocene time. During this interval, subsidence may have been more widespread than it is today because of the wetter climate and presumably greater rates of infiltration and transmissibility of ground water in the late Pleistocene (Carr and McGookey, in press). The moist climate of the late Pleistocene turned sinkholes and subsidence basins into pluvial ponds and lakes, the largest of which probably also received phreatic discharge. Limnic and lacustrine deposits occupy a stratigraphically consistent position in the Quaternary section of the western Rolling Plains. At one site, these deposits are more than 30 ft (9.1 m) thick and show evidence of structurally enhanced deposition.Bureau of Economic Geolog
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Radiocarbon Age of Quaternary Deposits, Western Rolling Plains of Texas
Four laboratories have made more than fifty finite radiocarbon-age determinations on samples from Quaternary deposits covering a large area of the Rolling Plains. These dates span the period from the late Pleistocene Epoch (23,255 ± 2,335 yr B.P.) virtually to the present. Caran and Baumgardner (1984) described a previously unrecognized sedimentary sequence covering more than 7,800 km2 (3,000 mi2) of northwestern Texas. At the time that report was prepared, only a few relevant radiocarbon-age determinations were available. The number of reliable finite dates has now increased to more than fifty, the oldest of which is 23,255 ± 2,335 yr B.P. Older infinite dates and a few questionable finite determinations also have been obtained, some of which were reported previously by other investigators.Bureau of Economic Geolog
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Lineaments of Texas---Possible Surface Expressions of Deep-Seated Phenomena
Geologic structures are important controls on geothermal resources. Buried plutons, intrusions, or diapirs may provide either localized areas of high heat flow or zones of high thermal conductivity. Various structures such as faults, joints, folds, or buried massifs may affect underground fluid flow and thus may alter local thermal regimes. These subsurface hydrologic effects may either enhance or detract from geothermal potential because upwelling of deep-seated fluids increases local geothermal gradient, but recharge decreases geothermal gradient. Geologic structures provide direct controls on heat flow and indirect controls on geothermal gradients via hydrologic processes. Understanding geologic structures, especially buried structures, will therefore aid in assessing the geothermal potential of a given area.
Some lineaments are surface indicators of geologic structures. An analysis of lineaments and an awareness of general hydrologic regimes provide means for delimiting promising areas for geothermal development. Lineaments, however, are polygenetic; not all linear features are related to earth structures at depth. Some are expressions of surface processes alone. Others seem to be essentially random alignments of features such as drainage, topography, soils, or vegetation, and the cause of many such features is unknown or ambiguous. Because of the varying quality of information imparted by individual lineaments, a high "noise-to-signal" ratio exists in lineament data. The geologist's task, in collecting lineament data and in subsequently analyzing them, is to winnow noise from signal—that is, to eliminate patterns that impart no geologic information, and thereby to ascertain which features are significant with respect to local or regional geologic structures. This process entails correlation of lineaments with other mapped features. For geothermal assessment, special emphasis must be placed on recognition of buried structures or other irregularities that may control thermal conditions in subsurface fluids.
Using lineament analysis for ascertaining geothermal potential entails a consideration of the structural (subsurface) control on surface features—especially the recurring motifs of aligned features that constitute regional or statewide linear trends or "grain." In places, lineaments are clearly correlative with buried structures. But lineaments also occur in areas without known subsurface discontinuities, and lineaments also occur in many places that have no geothermal potential. Thus, lineament analysis as a prospecting tool must be used carefully. Some workers have tended to assume that the very presence of a lineament invariably implies geologic control. The data we obtained do not support such a view, but they do indicate that many lineaments are expressions of local structural conditions that may be otherwise hidden or subtle.Bureau of Economic Geolog
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Geologic Review of Propsed Amarillo Area Site for the Superconducting Super Collider (SSC)
In June 1987, the Texas National Research Laboratory Commission commissioned the Bureau of Economic Geology at The University of Texas at Austin to conduct a review and brief report on the geology of the proposed site for the Superconducting Super Collider (SSC) in the Amarillo area. They also requested a surface geologic map of the site. An informal task force was assembled for this purpose, including Jay A. Raney (Coordinator), Thomas C. Gustavson, and S. Christopher Caran from the Bureau of Economic Geology. This report is accompanied by the geologic map (Plate 1) of the proposed Amarillo area site in the Texas Panhandle.Bureau of Economic Geolog
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Paleoclimatic Reconstruction Based on Molluscan (Gastropoda, Pelecypoda) Environmental Indicators-Late Quaternary of Northwestern Texas
Paleoecologic interpretation of fossil molluscan faunas provides a basis for indirect reconstruction of paleoclimates. Terrestrial and aquatic mollusks are abundant in late Quaternary sedimentary deposits of the western Rolling Plains of Texas. These taxa compose a succession of distinct faunal assemblages. Most mollusks represented in late Pleistocene to middle Holocene assemblages of the region are absent from the modern fauna. However, none of the extirpated species are extinct; their distribution has merely been reduced such that at present, these taxa are found northeast or in montane areas west of the Southern High Plains and Rolling Plains. Because they are living species, their environmental requirements, habitat, and climate are relatively well known. Environments that sustain these mollusks today are presumed to have existed in northwestern Texas in the past. Ecological conditions throughout the Pleistocene and Holocene Epochs can be inferred by tracing the range of environmentally sensitive taxa through radiocarbon-dated stratigraphic sequences. Allowance is made for local variations owing to facies changes and temporary modifications of habitat. Conditions in this region during the late Pleistocene favored diverse molluscan faunas. By comparison, the living fauna is depauperate and virtually restricted to species with broad environmental tolerances; climatic and ecological change was gradual, affecting different species at different times. Regional extirpation of a number of species with comparable ecologic requirements indicates a profound change in environment probably related to climate. Data from three well-constrained stratigraphic sections permit refinement of existing paleoclimatic reconstructions. Climatic variations during the Holocene have taken two related but somewhat independent paths. A summer warming trend that began in the latest Pleistocene greatly increased temperatures by about 8,000 years before present. A similar trend toward desiccation was accelerated between 8,000 and 6,000 years before present until essentially modern conditions were attained 3,000 years before present. Other, comparatively minor fluctuations of the regional paleoclimate are evident as well.Bureau of Economic Geolog