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At least 433 records · Page 24Linked to original sources
USGS2004

Allegheny woodrat (Neotoma magister) use of rock drainage channels on reclaimed mines in southern West Virginia

Allegheny woodrats ( Neotoma magister ) currently receive protected status throughout their range due to population declines. Threats associated with habitat fragmentation (e.g., introduced predators, disease, loss of connectivity among subpopulations and habitat loss) may explain why Allegheny woodrats are no longer found in many areas where they existed just 25 y ago. In southern West Virginia, surface coal mining is a major cause of forest fragmentation. Furthermore, mountaintop mining, the prevalent method in the region, results in a loss of rock outcrops and cliffs within forested areas, typical habitat of the Allegheny woodrat To determine the extent that Allegheny woodrats make use of reclaimed mine land, particularly rock drainages built during reclamation, we sampled 24 drainage channels on reclaimed surface mines in southern West Virginia, collected habitat data at each site and used logistic regression to identify habitat variables related to Allegheny woodrat presence. During 187 trap nights, 13 adult, 2 subadult and 8 juvenile Allegheny woodrats were captured at 13 of the 24 sites. Percent of rock as a groundcover and density of stems >15 cm diameter-at-breast-height (DBH) were related to Allegheny woodrat presence and were significantly greater at sites where Allegheny woodrats were present than absent. Sites where Allegheny woodrats were present differed substantially from other described habitats in West Virginia, though they may simulate boulder piles that occur naturally. Our findings suggest the need for additional research to examine the dynamics between Allegheny woodrat populations inhabiting rock outcrops in forests adjacent to mines and populations inhabiting constructed drainage channels on reclaimed mines. However, if Allegheny woodrats can use human-created habitat, our results will be useful to surface mine reclamation and to other mitigation efforts where rocky habitats are lost or disturbed.

West Virginia↗
USGS2012

Stratigraphic architecture of bedrock reference section, Victoria Crater, Meridiani Planum, Mars

The Mars Exploration Rover Opportunity has investigated bedrock outcrops exposed in several craters at Meridiani Planum, Mars, in an effort to better understand the role of surface processes in its geologic history. Opportunity has recently completed its observations of Victoria crater, which is 750 m in diameter and exposes cliffs up to ~15 m high. The plains surrounding Victoria crater are ~10 m higher in elevation than those surrounding the previously explored Endurance crater, indicating that the Victoria crater exposes a stratigraphically higher section than does the Endurance crater; however, Victoria strata overlap in elevation with the rocks exposed at the Erebus crater. Victoria crater has a well-developed geomorphic pattern of promontories and embayments that define the crater wall and that reveal thick bedsets (3–7m) of large-scale cross-bedding, interpreted as fossil eolian dunes. Opportunity was able to drive into the crater at Duck Bay, located on the western margin of Victoria crater. Data from the Microscopic Imager and Panoramic Camera reveal details about the structures, textures, and depositional and diagenetic events that influenced the Victoria bedrock. A lithostratigraphic subdivision of bedrock units was enabled by the presence of a light-toned band that lines much of the upper rim of the crater. In ascending order, three stratigraphic units are named Lyell, Smith, and Steno; Smith is the light-toned band. In the Reference Section exposed along the ingress path at Duck Bay, Smith is interpreted to represent a zone of diagenetic recrystallization; however, its upper contact also coincides with a primary erosional surface. Elsewhere in the crater the diagenetic band crosscuts the physical stratigraphy. Correlation with strata present at nearby promontory Cape Verde indicates that there is an erosional surface at the base of the cliff face that corresponds to the erosional contact below Steno. The erosional contact at the base of Cape Verde lies at a lower elevation, but within the same plane as the contact below Steno, which indicates that the material above the erosional contact was built on significant depositional paleotopography. The eolian dune forms exposed in Duck Bay and Cape Verde, combined with the geometry of the erosional surface, indicate that these outcrops may be part of a larger-scale draa architecture. This insight is possible only as a result of the larger-scale exposures at Victoria crater, which significantly exceed the more limited exposures at the Erebus, Endurance, and Eagle craters.

Book chapter↗
USGS2007

Steeply dipping heaving bedrock, Colorado: Part 3 - Environmental controls and heaving processes

This paper examines the environmental processes and mechanisms that govern differential heaving in steeply dipping claystone bedrock near Denver, Colorado. Three potential heave mechanisms and causal processes were evaluated: (1) rebound expansion, from reduced overburden stress; (2) expansive gypsum-crystal precipitation, from oxidation of pyrite; and (3) swelling of clay minerals, from increased ground moisture. First, we documented the effect of short-term changes in overburden stress, atmospheric exposure, and ground moisture on bedrock at various field sites and in laboratory samples. Second, we documented differential heaving episodes in outcrops and at construction and developed sites. We found that unloading and exposure of the bedrock in construction-cut areas are essentially one-time processes that result in drying and desiccation of the near-surface bedrock, with no visible heaving response. In contrast, wetting produces a distinct swelling response in the claystone strata, and it may occur repeatedly as natural precipitation or from lawn irrigation. We documented 2.5 to 7.5 cm (1 to 3 in.) of differential heaving in 24 hours triggered by sudden infiltration of water at the exposed ground surface in outcrops and at construction sites. From these results, we interpret that rebound and pyrite weathering, both of which figure strongly into the long-term geologic evolution of the geologic framework, do not appear to be major heave mechanisms at these excavation depths. Heaving of the claystone takes two forms: (1) hydration swelling of dipping bentonitic beds or zones, and (2) hydration swelling within bedrock blocks accommodated by lateral, thrust-shear movements, along pre-existing bedding and fracture planes.

Environmental & Engineering Geoscience↗
USGS2018

New insights on scale-dependent surface-groundwater exchange from a floating self-potential Dipole

In south-central Texas the lower Guadalupe River has incised into the outcrop of the Carrizo-Wilcox aquifer. The river and the aquifer are hydraulically connected across the outcrop, although the connectivity is obscured at the surface by alluvium and surface-water and groundwater exchange dynamics are currently poorly understood. To investigate surface-water and groundwater exchange dynamics between the lower Guadalupe River and the Carrizo-Wilcox aquifer, a geophysical study was completed along a 14.86 km reach of the river by using water-borne gradient self-potential (SP) profiling and two-dimensional direct-current electric resistivity tomography. This paper explores the applicability of these water-borne geoelectric methods in delineating gaining and losing channel reaches, and demonstrates that geoelectric signals in the form of total electric field strength can be logged with an electric dipole and decomposed into component SP signals depicting regional and local groundwater flow patterns attributable to regional and localized hydraulic gradients. Localized SP anomalies of several tens of millivolts, indicative of hyporheic exchange flows, are observed and superimposed upon a 124 mV regional SP anomaly indicative of ambient groundwater exchange flows between the river and the aquifer. The observed SP signals are interpreted through two-dimensional finite-element modeling of streaming potentials attributable to ambient groundwater exchange and hyporheic exchange flow patterns. Variables of the channel environment such as temperature and concentration gradients, depth, and velocity are considered and subsequently eliminated as alternative sources of the SP signals that are presented.

Texas↗
USGS2026

Apatite (U-Th)/He thermochronology from Marsh Creek anticline reconciles Cenozoic and Holocene strain patterns and elucidates the Cenozoic canning displacement zone of Arctic Alaska

The northeastern Brooks Range is a vast fold-thrust belt that records the northernmost expression of Cenozoic deformation in Alaska, likely with complex dynamic linkages to distant tectonic elements. The principal focus of this manuscript is the Marsh Creek anticline (MCA), which is a large and recently active structure within the broader northeastern Brooks Range. The MCA is a complex, polyphase structure mostly buried beneath the Arctic coastal plain. We present apatite (U-Th)/He (AHe) dates from six outcrop samples, all near the structural crest of the anticline, as well as supporting detrital zircon U/Pb (ZUPb) age spectra from five outcrop samples. The AHe sample transect spans ~3 km of structural relief. The four shallowest AHe samples are not reset. However, the two deepest samples exhibit low intrasample variability among replicates and strong date versus grain radius correlations, suggesting post-depositional burial heating to within the AHe partial retention zone. Inverse thermal history modeling of these data resolves a protracted phase of exhumational cooling that began around 33–28 Ma. Detrital ZUPb age spectra from Paleogene strata support an interpretation of diverse inherited thermal histories recorded by the AHe data, and they are also consistent with extant reconstructions of Paleogene sediment dispersal. Placed into regional context, the results constrain a phase of increasing structural relief in the northeastern Brooks Range fold-thrust belt that began by the Eocene. The relief developed in a zone characterized by diminishing structural relief to the west called the Canning displacement zone. Although this zone was active since the Eocene, several structures including the studied part of the MCA were rapidly exhumed in the Oligocene. Lastly, we argue for kinematic compatibility between Cenozoic contraction and active strike-slip in the northeastern Brooks Range, with the temporal change in strain style likely reflecting the increase in structural relief and topography.

Alaska↗
USGS1999

Carboniferous and older carbonate rocks: Lithofacies, extent, and reservoir quality: Chapter CC in The oil and gas resource potential of the Arctic National Wildlife Refuge 1002 area, Alaska

Carboniferous and older carbonate rocks are potential hydrocarbon reservoir facies for four plays in the 1002 area of the Arctic National Wildlife Refuge. These rocks include several units in the pre-Carboniferous basement and the Carboniferous Lisburne Group. Data from exploratory wells west of the 1002 area, outcrops south of the 1002 area, seismic lines, and well logs are synthesized herein to infer carbonate lithofacies, extent, and reservoir character beneath the northeastern Arctic coastal plain. A chiefly shallow-water basement carbonate succession of Late Proterozoic through Early Devonian age (Katakturuk Dolomite, Nanook Limestone, and Mount Copleston Limestone) is interpreted to be present beneath much of the south-central 1002 area; it reaches 3,700 m thick in outcrop and is the primary reservoir for the Deformed Franklinian Play. A more heterogeneous lithologic assemblage of uncertain age forms basement in the northwestern part of the 1002 area; well data define three subunits that contain carbonate intervals 5- 50 m thick. These strata are prospective reservoirs for the Undeformed Franklinian Play and could also be reservoirs for the Niguanak- Aurora Play. Regional lithologic correlations suggest a Cambrian-Late Proterozoic(?) age for subunits one and two, and a slightly younger, later Cambrian-Silurian age for subunit three. Seismic and well data indicate that subunit one overlies subunit two and is overlain by subunit three. The Mississippian and Pennsylvanian Lisburne Group, a predominantly carbonate platform succession as much as 1 km thick, is projected beneath the southernmost part of the 1002 area and is a potential reservoir for the Ellesmerian Thrust-belt and Niguanak-Aurora Plays. Carbonate rocks in the 1002 area probably retain little primary porosity but may have locally well developed secondary porosity. Measured reservoir parameters in basement carbonate strata are low (porosity generally ≤ 5%; permeability ≤ 0.2 md) but drill-stem tests found locally reasonable flow rates (4,220-4,800 bpd) and, in the Flaxman Island area, recovered gas and condensate from these rocks. The Lisburne Group has produced up to 50,000 bbl of oil/ day from the Lisburne field at Prudhoe Bay. Reservoir parameters of the Lisburne in northeastern Alaska range from low (porosities ≤ 5% in most limestones) to good (porosities average 6.5-10% in some dolostones). Reservoir quality in Carboniferous and older carbonate strata in the 1002 area should be greatest where these rocks are highly fractured and (or) truncated by the Lower Cretaceous Unconformity.

Alaska↗
USGS1949

Heavy mineral zonation of Cretaceous and Tertiary rocks of the central area of northern Alaska

This report presents the general conclusions pertaining to the correlation of Cretaceous and Tertiary rocks in test wells and outcrops in the central area of northern Alaska (fig. 1) by means of heavy minerals. Approximately 1.000 drill and outcrop samples have been studied. In order to relate the materiel here presented to the regional geologic picture of the central area, the restored facies cross-sections A-A' and B-B' of T.G. Payne 1/ are used as a basis for the graphic presentation of the heavy mineral zonation. Section C-C' of Payne is not used because most of it lies outside the area treated in this report and because of new geological and geophysical interpretations in the Barrow area as the result of recent exploration. Instead, the heavy mineral zonation along a somewhat different section C-C' (see fig. 1) is discussed but not illustrated.

Alaska↗
USGS1947

Preliminary report on the stratigraphy and structure of the Titaluk and upper Ikpikpuk Rivers, Alaska

Geological Survey Party No. 4 was assigned an investigation of the Ikpikpuk and Titaluk Rivers and East Fork of the Ikpikpuk River mainly for the purpose of obtaining stratigraphic information which would be of use in determining the parts of the Upper Cretaceous sequence that underlie the areas investigated by United Geophysical Company parties 43 and 46. A total of five days were spent in geological investigations of the Titaluk River with a Cub plane equipped with pontoons. The party was composed of the geologist and Don Hulshizer, pilot of Wien Alaska Airlines. The geologist and Ronald K. Sorem, field assistant, traversed the Ikpikpuk River by boat from the junction of Maybe Creek and the Kigalik River to near the junction of the East Fork. From the northernmost point reached by boat traverse, the river was examined by plane to north of latitude 70° N., but no outcrops or rubble indicating bedrock were seen. The East Fork was also examined from the air but no outcrops or rubble were observed.

Alaska↗
USGS1963

Geology of the Inyan Kara Mountain quadrangle, Crook and Weston Counties, Wyoming

The Inyan Kara Mountain quadrangle includes about 215 square miles on the west side of the Black Hills, in Crook and Weston Counties, Wyo. It is about 10 miles south of Sundance, 6 miles east of Upton, and 10 miles northeast of Newcastle, Wyo. Exposed sedimentary rocks, exclusive of surficial deposits, are about 4,000 feet thick and range in age from Mississippian to Cretaceous. Sandstone, siltstone, and shale make up most of the sedimentary sequence; limestone, gypsum, bentonite, and coal are present in lesser quantities. The Pahasapa limestone of Mississippian age is the oldest formation exposed. It is overlain by the Minnelusa formation of Pennsylvanian and Permian age, followed in turn by the Opeche formation and Minnekahta limestone of Permian age, the Spearfish formation of Permian and Triassic age, the Gypsum Spring, Sundance, and Morrison formations of Jurassic age, and the Lakota, Fall River, Skull Creek, Newcastle, Mowry, Belle Fourche, Greenhorn, and lower part of the Carlile formations of Cretaceous age. A small plug of syenite porphyry that crosscuts all formations from the Pahasapa to the Spearfish crops out at Inyan Kara Mountain in the northern part of the quadrangle. The sedimentary rocks have a fairly uniform dip of 1 to 3 degrees to the southwest. This simple monoclinal structure is interrupted by sharply folded domes at Inyan Kara and nearby Strawberry Mountains in the northern part of the quadrangle. The Inyan Kant Mountain dome is about 1 1/2 miles across and has about 1,800 feet of structural closure in the outcropping Pahasapa limestone and younger rocks. A fault with a curving trace open to the northeast outlines the fold. Igneous and sedimentary rocks within the area circumscribed by the fault are upthrown as much as 600 feet. The Strawberry Mountain dome is about 11/2 miles across and has about 450 feet of closure; the Minnelusa is the oldest formation exposed on the crest of the fold. Other less sharply folded anticlines or domes involve outcrops of the Opeche, Minnekahta, and Spearfish formations in the northeast corner of the quadrangle; the Sundance formation along Oil Creek in the southeastern part; and the Skull Creek, Newcastle, and Mowry formations near Turner Creek in the southeastern part. Mineral resources include oil in the Newcastle, Mowry, and Belle Fourche formations at the Osage oil field, which extends about a mile into the southwestern part of the quadrangle ; gypsum in the Gypsum Spring and Spearfish formations ; small amounts of bituminous coal in the Lakota formation ; bentonite in the Newcastle, Mowry, and Belle Fourche formations; and sand and gravel from stream terraces.

Wyoming↗
USGS1993

Stratigraphy of the late Proterozoic Murdama Group, Saudi Arabia

The Murdama group is in the upper part of the sequence of Proterozoic layered rocks in the Precambrian shield of Saudi Arabia. It consists of clastic sedimentary rocks and small amounts of limestone and volcanic rocks. The Murdama crops out in the eastern part of the exposed part of the shield, within 200 km of its margin. The principal outcrop area, herein designated the Afif belt, is 600 km long and has a maximum width of 80 km. Two other significant outcrop areas lying to the south are designated the Jabal Hadhah and the Mistahjed belts. The Murdama group unconformably overlies older plutonic rocks that range in composition from diorite to granite and volcanic rocks ranging from basalt to rhyolite. It is unconformably overlain in the north part of the Afif belt by sedimentary and volcanic rocks of the Jurdhawiyah group, and in many areas is intruded by younger granite. In the south part of the Afif belt the Murdama group lies in the Maslum synclinorium, a structure characterized by tight folding near its northwest margin and open folding elsewhere. To the north, the synclinorium is much broken up by faulting, particularly by left-lateral faults of the Najd system. Sections on the west flank of the Mast urn synclinorium in the south part of the Afif belt have apparent thicknesses of about 5,300 m at Jabal Murdama, 5,700 m at Jabal Raqabah, and 1 ,400 and 4,000 m at As Sawadah. The strata in these sections consist mostly of greenish-gray, very fine to coarse-grained volcanic arenite that is poorly sorted and consists of angular grains. Basal conglomerates are thin and inconspicuous, but coarse arenite, locally pebbly, predominates in the jabal Raqabah section. A prominent air-fall ash tuff caps Jabal Murdama, and an ash-flow tuff caps Jabal Raqabah. Sections on the east flank of the synclinorium have apparent thicknesses of about 2,500 m at Jabal Farida, 3,600 m at Jabal Damkh, 12,400 m at Jabal Zaydi, and 16,800 m, adjusted for folding, at Wadi Sirrah. Jabal Farida and Jabal Damkh are underlain principally by limestone of distinctive tan- and gray-weathering types, which has been named the Farida marble. Limestones of these and other colors occur in all the belts composing the Murdama and form a unifying element. The other sections consist mostly of sandstone similar to that at Jabal Murdama. Sections in the north part of the Afif belt have apparent thickness of about 3,300 and 7,600 m at Wadi Jarir, 840 m at Jabal Ajam, 534 and 1,833 m at Jabal Muwasham, about 3,800 m adjusted for folding east of jabal Silsillah, 4,900 m at Jabal Khidar, and 8,400 m at jabal umm Sammah. The Wadi Jarir section consists of sandstone very similar to that at Jabal Murdama, with thin basal conglomerate and local ash tuff. The other sections consist of conglomerate, sandstone, and siltstone. The predominance of silicic volcanic lithic grains in Murdama sandstones of the Afif belt indicates a source in a silicic volcanic belt, and discontinuous belts of such rocks lie to the southwest. Paleocurrent indicators also suggest a source from the southwest. In the north part of the belt, the lower part of the Murdama is probably a subaerial mass-movement or fluvial deposit. The strata in the rest of the belt were probably deposited at a prograding lacustrine or marine strandline. Near the northwest edge of the basin, particularly from Jabal Farida north, locally derived conglomerate was deposited and carbonate bank deposition prevailed for a time. In the jabal Hadhah belt, limestone is identical to that at Jabal Farida. It is apparently overlain by conglomerate that fines upward to sandstone and may be part of the Murdama. Structure in the Mistahjed belt is more complex and the stratigraphic sequence is less certain than in the Afif belt. Murdama rocks have been assigned to a number of formations, and traverses were made across most units. The rocks include sandstone, siltstone, limestone, conglomerate, and volcanic rock; much of the volcanic rock may not be part of the Murdama group. The source of sedimentary materials in the Mistahjed belt, as in the Afif belt, appears to be a belt of volcanic rocks lying to the southwest. The Junaynah belt of sedimentary rocks lies to the west of the Mistahjed belt. The rocks consist of basal cobble conglomerate grading up to coarse- and finegrained sandstone. These rocks have been assigned to the Murdama group in the past, but I conclude that they should be restricted from it, because their tectonic setting and age appear to be different. Radiometric ages suggest an age range of 650 to 615 Ma for the Murdama group, the laterally equivalent Hibshi formation, and the overlying Jurdhawiyah group in the Afif belt. Ages from the Mistahjed belt suggest that the Murdama rocks there are younger than 650 Ma and ages Abstract from the junaynah area suggest that the sedimentary section is younger than 61 0 Ma. The Murdama group probably was deposited in a back-arc basin on a continental platform bounded on the west by an active volcanic arc above an east-dipping subduction zone. The position of the subduction zone, which was active during most of the deposition in the Afif belt, is marked by a belt of gabbro and ultramafic rocks herein named the jabal Burqah belt. The subduction zone later stepped out to the southwest to the Nabitah belt, and Murdama strata were deposited in the Jabal Hadhah, Mistahjed, and smaller basins.

Bulletin↗
USGS2001

Potential for deep basin-centered gas accumulation in Hanna Basin, Wyoming

The potential for a continuous-type basin-centered gas accumulation in the Hanna Basin in Carbon County, Wyoming, is evaluated using geologic and production data including mud-weight, hydrocarbon-show, formation-test, bottom-hole-temperature, and vitrinite reflectance data from 29 exploratory wells. This limited data set supports the presence of a hypothetical basin-centered gas play in the Hanna Basin. Two generalized structural cross sections illustrate our interpretations of possible abnormally pressured compartments. Data indicate that a gas-charged, overpressured interval may occur within the Cretaceous Mowry, Frontier, and Niobrara Formations at depths below 10,000 ft along the southern and western margins of the basin. Overpressuring may also occur near the basin center within the Steele Shale and lower Mesaverde Group section at depths below 18,000 to 20,000 ft. However, the deepest wells drilled to date (12,000 to 15,300 ft) have not encountered over-pressure in the basin center. This overpressured zone is likely to be relatively small (probably 20 to 25 miles in diameter) and is probably depleted of gas near major basement reverse faults and outcrops where gas may have escaped. Water may have invaded reservoirs through outcrops and fracture zones along the basin margins, creating an extensive normally pressured zone. A zone of subnormal pressure also may exist below the water-saturated, normal-pressure zone and above the central zone of overpressure. Subnormal pressures have been interpreted in the center of the Hanna Basin at depths ranging from 10,000 to 25,000 ft based on indirect evidence including lost-circulation zones. Three wells on the south side of the basin, where the top of the subnormally pressured zone is interpreted to cut across stratigraphic boundaries, tested the Niobrara Formation and recovered gas and oil shows with very low shut-in pressures.

Bulletin↗
USGS1954

Stripping-coal deposits on lower Lignite Creek, Nenana coal field, Alaska

Stripping-coal reserves in an area of about 9.4 square miles extending from the Nenana River about 6 miles up the valley of Lignite Creek are estimated to amount to about 95, 000, 000 tons. The stripping-coal reserves are located in the lower and middle members of the Tertiary coal-bearing formation. Five continuous beds in the middle member range in thickness from 5 to 30 feet, and a discontinuous bed at the base of the lower member is about 60 feet thick. Analyses of outcrop samples, as received at the laboratory, show a heating content of 7,500--8,200 Btu, an ash content of 6 to 14 percent, and a moisture content of 25 percent. The reserve estimate is based on a maximum thickness of overburden of 200 feet. Coal below the level of Lignite Creek or its major tributaries was not considered as it was assumed that stripping would be by hydraulic methods. Uncertainties regarding the position of the coal outcrops and the extent of burning of the coal beds are the basis for a recommendation that, where possible, the stripping reserves be tested by drilling. Overburden consists largely of weakly consolidated sandstone and includes some coarse gravel and a few boulders 20 feet or more in diameter. Water for hydraulic mining can be obtained from the Nenana River. Lignite Creek does not appear to be a dependable source. Disposal of debris may affect the channel of the Nenana River causing damage to railroads and structures. Landslides are common in the valley of Lignite Creek and will affect mining operations and transportation routes.

Circular↗
USGS1961

Availability of ground water in the Gallup area, New Mexico

A thick succession of sedimentary rocks (about 6,000 feet) underlies the town of Gallup and crops out nearby. Although all the sedimentary rocks are capable of yielding some water, only a few units of sandstone and limestone yield water in sufficient quantity and of acceptable quality to be considered as sources of large supplies. The five stratigraphic units that are most productive of ground water form three aquifers, as follows: (a) the Glorieta sandstone and San Andres limestone, (b) the Westwater Canyon member of the Morrison formation and the Dakota sandstone, and (e) the Gallup sandstone. The Glorieta sandstone yields only small amounts of water to wells, except where it is intensely fractured. It probably contributes large amounts of water to the overlying, more permeable San Andres limestone by slow vertical leakage over large areas, as water is withdrawn from the San Andres. The San Andres limestone is discontinuous in the eastern part of the area, wedging out entirely a few miles east of Gallup. Its permeability varies widely because locally the permeability has been greatly increased by fractures and solution channels. On the north flank of the Zuni Mountains, near its outcrop, the San Andres yields as much as 1,100 gpm (gallons per minute) of water to wells. The specific capacity of wells that tap the aquifer formed by this Glorieta sandstone and San Andres limestone ranges from 0.1 to 29 gpm per foot of drawdown. In general, the water in the Glorieta sandstone and San Andres limestone is hard, because it contains much calcium. Both bicarbonate and sulfate anions are abundant. The chemical quality of the water deteriorates with increasing distance from the outcrop. The Westwater Canyon member of the Morrison formation and the Dakota sandstone form a single hydrologic unit extending from about 5 miles east of Gallup westward into Arizona. To the east they are separated by shale of the Brushy Basin member of the Morrison formation. The water-bearing properties of the Westwater Canyon member and the Dakota sandstone are ill defined, because few wells in the area tap either of them exclusively. The specific capacity of wells that tap the Westwater Canyon member, the Dakota sandstone, or both ranges from 0.02 to 2.3 gpm per foot of drawdown. Water in this aquifer generally contains less that 1,000 ppm (parts per million) of dissolved solids. The concentration of sodium and bicarbonate typically is high, and the concentration of sulfate is high locally. The Gallup sandstone is the principal aquifer in the immediate vicinity of, and to the north and south of, Gallup. It yields as much as 260 gpm of water to wells; the specific capacity of wells that tap the Gallup sandstone ranges from 0.08 to 4.7 gpm per foot of drawdown. In general, the water in the Gal]up sandstone is potable, although in places it yields water high in iron, sulfate, and dissolved solids; the concentration of dissolved solids generally is less than 1,000 ppm. Because the yields of all the formations tested at Gallup are small, the town needs a better source of water. The San Juan River discharges annually a larger volume of water than is available from any other source in northwestern New Mexico. Gallup has applied for 15,000 acre-feet of San Juan River water a year, an average of 13,400,000 gpd (gallons per day). This water would be expensive, because about 50 miles of pipeline would be required to transport the water, and it would have to be liked about 1,000 feet over a high ridge north of town. Despite the expense involved, at this time the San Juan River seems to offer the most secure long-term supply of water for the Gallup area.

New Mexico↗
USGS1934

Geology of the North and South McCallum anticlines, Jackson County, Colorado, with special reference to petroleum and carbon dioxide

The McCallum anticlines, embracing an area about 2 miles wide and 12 miles long, are about 6 miles east of the town of Walden, Jackson County, Colo., on the east side of the Continental Divide. A cover of flat-lying Quaternary gravel obscures the outcrop of Pierre shale at many points on the two anticlines. Wells start in the upper part of the Pierre and penetrate all of the underlying Upper Cretaceous series to the top of the Dakota sandstone, where production of oil and carbon dioxide is obtained. The first prospecting for oil was reported in 1912, but it was not until December 1926 that oil was discovered in commercial quantities. Two geologic sections across the anticlines, extending to the outcrop of the Dakota sandstone at the base of the Medicine Bow Range, to, the east, disclosed a marked thickening between this formation and a fossiliferous sandstone in the Pierre shale which was used as a key bed. Immediately beneath the Dakota sandstone along ore of these cross sections a sandy volcanic ash resembling that found at the horizon of the Mowry shale in Wyoming was discovered. However, it is considered here the top bed of the Morrison formation. The impossibility of obtaining dips along the crests, owing to the cover of terrace gravel, made it necessary to construct ten structure sections across these anticlines, using the geometry of conic sections in their development. From the geometric figures developed structure contours were obtained graphically. The occurrence of carbon dioxide in large volumes in association with petroleum on each of these anticlines provides an unusual problem in oil production. Experimental data relative to the physical properties of this gas offer an approach to the solution of the problem. The applicability of such data to actual operating conditions is yet to be tried, but the work of early investigators in the field of physical chemistry suggests the feasibility of mixing air with the carbon dioxide to assure continuity of production, which heretofore has not been attained in this area.

Colorado↗
USGS1950

A glossary of uranium- and thorium-bearing minerals

During 1980, an estimated 121 million gallons of water per day was pumped in a 26-county area in east-central Georgia from sand aquifers of Paleocene and Late Cretaceous age. Maximum withdrawals were at the kaolin mining and processing centers in Twiggs, Wilkinson, and Washington Counties, where water levels have declined as much as 50 ft since 1944-50. In the southern two-thirds of the study area, water levels have shown little, if any, change. Declining water levels and increasing competition for groundwater have caused concern over the adequacy of groundwater supplies. This report defines the areal extent and describes the geohydrology of the Paleocene-Upper Cretaceous aquifers of east-central Georgia, and evaluates the effects of man on the groundwater flow system. Geohydrologic data from four test wells indicate that the aquifers consist of alternating layers of sand and clay that are largely of deltaic origin. In the northern third of the study area, the confining unit between the Dublin and Midville aquifer systems is absent and the aquifer systems combine to form the Dublin-Midville aquifer system. The aquifer systems range in thickness from 80 to 645 ft and their transmissivities range from 800 to 39,000 sq ft/day. The hydraulic conductivity ranges from 15 to 530 ft/day. Wells yield as much as 3,400 gpm (gallons per minute). Chemical analyses of water from 49 wells indicate that water from both aquifer systems is of good quality except in the central part of the study area, where iron concentrations are as high as 6,700 micrograms/L and exceed the 300 micrograms/L recommended limit for drinking water. The principal recharge to the aquifer systems is from precipitation that occurs within and adjacent to the outcrop areas. The principal discharge is to streams in the outcrop area. (Author 's abstract)

Circular↗
USGS1951

Selected abstracts on engineering geology and related subjects

Interlayered sand, silt, and clay of middle Eocene to late Paleocene age in east-central Georgia form the Gordon aquifer system which ranges in thickness from about 20 to 180 ft. Estimated transmissivities range from 620 to 13,000 sq ft/day. During 1980, approximately 24 million gpd (gallons per day) was withdrawn from the Gordon aquifer system, of which about 70% was used for irrigation. Water levels in the aquifer throughout the study area generally showed little change during 1934-68; however, during 1969-81, local declines as great as 33 ft have occurred in areas of increased irrigation or large scale municipal and industrial pumping. The Gordon aquifer system is recharged by precipitation in the outcrop area and in interstream drainage divides in and near the outcrop area, and by leakage through adjacent confining units. Discharge from the aquifer occurs predominantly as flow into streams or as leakage into underlying and overlying units. Water from the Gordon aquifer system is generally a calcium bicarbonate type that ranges from soft to hard, and in most areas has constituent concentrations that are within the Georgia Environmental Protection Division recommended drinking water standards. (Author 's abstract)

Circular↗
USGS2005

Water-level altitudes in wells completed in the northern segment of the Edwards Aquifer, Travis, Williamson, and Bell Counties, Texas, March-June 2005

During March-June 2005, the U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality (TCEQ), measured water levels in 80 Edwards aquifer wells in the outcrop of the northern segment of the aquifer in Travis, Williamson, and Bell Counties. Public-supply and private wells were selected in areas where outcrop water-level data were sparse. The altitude data can be used in the TCEQ Source Water Assessment and Protection program to help delineate zones of capture around sources of public water supply. Altitudes range from about 490 to about 935 feet above North American Vertical Datum of 1988.

Texas↗
USGS1999

Distribution of hydrogeologic units in the Black Hills area, South Dakota

This report is a product of the Black Hills Hydrology Study, which was initiated in 1990 to assess the quantity, quality, and distribution of surface water and ground water in the Black Hills area of South Dakota (Driscoll, 1992). This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators. The map in this report is part of a series of 1:100,000-scale maps that are being produced for the study. Other maps include structure-contour maps (altitudes of the tops of formations) for five formations that contain major aquifers in the study area, and potentiometric maps for these five major aquifers (the Inyan Kara, Minnekahta, Minnelusa, Madison, and Deadwood aquifers). The study area consists of the topographically defined Black Hills and adjacent areas located in western South Dakota. The Black Hills area is an elongated, dome-shaped feature, about 125 miles long and 60 miles wide, which was uplifted during the Laramide orogeny (Feldman and Heimlich, 1980). The oldest geologic units in the study area are Precambrian metamorphic and igneous rocks, which are exposed in the central core of the Black Hills. Surrounding the Precambrian core is a layered series of sedimentary rocks including limestones, sandstones, and shales that are exposed in roughly concentric rings around the uplifted flanks of the Black Hills. The bedrock sedimentary units typically dip away from the uplifted Black Hills at angles that approach or exceed 10 degrees near the outcrops, and decrease with distance from the uplift. Many of the sedimentary units contain aquifers, both within and beyond the study area. Recharge to these aquifers occurs from infiltration of precipitation upon the outcrops and, in some cases, from infiltration of streamflow (Hortness and Driscoll, 1998). Artesian conditions generally exist within these aquifers where an upper confining layer is present. Flowing wells and artesian springs that originate from confined aquifers are common around the periphery of the Black Hills.

Hydrologic Atlas↗