Central Wyoming Research Articles

Waterborne outbreak of gastroenteritis associated with a norovirus.

The Wyoming Department of Health investigated an outbreak of acute gastroenteritis among persons who dined at a tourist saloon in central Wyoming during October 2001. Human caliciviruses (HuCVs) were suspected as the etiological agent of the outbreak based on the incubation period, duration of illness, and symptoms observed in ill patrons. A retrospective cohort study demonstrated that ill patrons were 4.5 times more likely to have exposure to drinking water and/or ice than nonill patrons. No food items were associated with illness. An environmental investigation gave evidence that the saloon's groundwater was contaminated with sewage. Water from the saloon's only well was processed for viruses. The processed water sample and stool samples collected from three ill patrons were analyzed by reverse transcription-PCR (RT-PCR) for the presence of HuCV. All positive RT-PCR results were confirmed by sequence and phylogenetic analyses of cloned RT-PCR products. A genogroup I, subtype 3, HuCV stain was found to be present in the well water sample and two stool samples. In addition, a genogroup II, subtype 6, strain was detected in one stool sample. The identification of the same HuCV strain in both the well water and stool samples strongly suggests a link between exposure to well water and the outbreak of gastroenteritis. The presence of a genogroup II, subtype 6, strain in one of the stool samples suggests that multiple HuCV strains may have been involved in this outbreak. The laboratory isolation of HuCV strains from outbreak-associated drinking water is relatively novel in the United States. This investigation outlines the procedure for virus isolation and illustrates the utility of RT-PCR for the identification of HuCV in large volumes of water and stool samples obtained during outbreaks of acute nonbacterial gastroenteritis.

Prevalence of antibodies to Neospora caninum, Sarcocystis neurona, and Toxoplasma gondii in wild horses from central Wyoming.

Sarcocystis neurona, Neospora caninum, N. hughesi, and Toxoplasma gondii are 4 related coccidians considered to be associated with encephalomyelitis in horses. The source of infection for N. hughesi is unknown, whereas opossums, dogs, and cats are the definitive hosts for S. neurona, N. caninum, and T. gondii, respectively. Seroprevalence of these coccidians in 276 wild horses from central Wyoming outside the known range of the opossum (Didelphis virginiana) was determined. Antibodies to T. gondii were found only in 1 of 276 horses tested with the modified agglutination test using 1:25, 1:50, and 1:500 dilutions. Antibodies to N. caninum were found in 86 (31.1%) of the 276 horses tested with the Neospora agglutination test--the titers were 1:25 in 38 horses, 1:50 in 15, 1:100 in 9, 1:200 in 8, 1:400 in 4, 1:800 in 2, 1:1,600 in 2, 1:3,200 in 2, and 1:12,800 in 1. Antibodies to S. neurona were assessed with the serum immunoblot; of 276 horses tested, 18 had antibodies considered specific for S. neurona. Antibodies to S. neurona also were assessed with the S. neurona direct agglutination test (SAT). Thirty-nine of 265 horses tested had SAT antibodies--in titers of 1:50 in 26 horses and 1:100 in 13. The presence of S. neurona antibodies in horses in central Wyoming suggests that either there is cross-reactivity between S. neurona and some other infection or a definitive host other than opossum is the source of infection. In a retrospective study, S. neurona antibodies were not found by immunoblot in the sera of 243 horses from western Canada outside the range of D. virginiana.

Cloud Creek structure, central Wyoming, USA: Impact origin confirmed

Abstract— The circular Cloud Creek structure in central Wyoming, USA is buried beneath ˜1200 m of Mesozoic sedimentary rocks and has a current diameter of ˜7 km. The morphology/morphometry of the structure, as defined by borehole, seismic, and gravity data, is similar to that of other buried terrestrial complex impact structures in sedimentary target rocks, e.g., Red Wing Creek in North Dakota, USA. The structure has a fault‐bordered central peak with minimum diameter of ˜1.4 km, composed predominantly of Paleozoic carbonates thickened by thrust faulting and brecciation, and is elevated some 520 m above equivalent strata beyond the outer rim of the structure. There is a ˜1.6 km wide annular trough sloping away from the central peak (maximum structural relief, 300 m) and terminated by a detached, fault‐bounded, rim anticline. The youngest rocks within the structure are Late Triassic (Norian?) clastics and these are overlain unconformably by post‐impact Middle Jurassic (Bathonian?) sandstones and shales. Thus, the formation of the Cloud Creek structure is dated chronostratigraphicly as ˜190 ± 20 Ma.Reported here for the first time are measurements of planar deformation features (PDFs) in shocked quartz grains in thin sections made from drill cuttings recovered in a borehole drilled at the southern perimeter of the central peak. Other, less definitive microstructures consistent with impact occur in samples collected from boreholes drilled into the central peak and rim anticline. The shock‐metamorphic evidence confirms an impact origin for the Cloud Creek structure.

A New Pterosaur Tracksite from the Jurassic Summerville Formation, Near Ferron, Utah

Pterosaur tracks (cf. Pteraichnus) from the Summerville Formation of the Ferron area of central Utah add to the growing record of Pteraichnus tracksites in the Late Jurassic Summerville Formation and time-equivalent, or near time-equivalent, deposits. The site is typical in revealing high pterosaur track densities, but low ichnodiversity suggesting congregations or “flocks” of many individuals. Footprint length varies from 2.0 to 7.0 cms. The ratio of well-preserved pes:manus tracks is about 1:3.4. This reflects a bias in favor of preservation of manus tracks due to the greater weight-bearing role of the front limbs, as noted in other pterosaur track assemblages. The sample also reveals a number of well-preserved trackways including one suggestive of pes-only progression that might be associated with take off or landing, and another that shows pronounced lengthening of stride indicating acceleration. One well-preserved medium-sized theropod trackway (Therangospodus) and other larger theropod track casts (cf. Megalosauripus) are associated with what otherwise appears to be a nearly monospecific pterosaur track assemblage. However, traces of a fifth pes digit suggest some tracks are of rhamphorynchoid rather than pterodactyloid origin, as usually inferred for Pteraichnus. The tracks occur at several horizons in a thin stratigraphic interval of ripple marked sandstones and siltstones. Overall the assemblage is similar to others found in the same time interval in the Western Interior from central and eastern Utah through central and southern Wyoming, Colorado, northeastern Arizona, and western Oklahoma. This vast “Pteraichnus ichnofacies,” with associated saurischian tracks, remains the only ichnological evidence of pre-Cretaceous pterosaurs in North America and sheds important light on the vertebrate ecology of the Summerville Formation and contiguous deposits.

Effects of Environmental and Land Use Regulation in the Oil and Gas Industry Using the Wyoming Checkerboard as an Experimental Design

This paper estimates the extra costs of drilling for oil and gas on federal land as compared to private land in the Wyoming Checkerboard. The Checkerboard, an important site of recent oil and gas activity, is a 40-mile-wide strip of land, 20 miles on each side of the Union Pacific Railroad right-of-way, extending westward approximately 200 miles from Rawlins in south central Wyoming to the Utah state line. The Pacific Railway Acts of 1862 and 1864 conveyed to the railroad both surface and mineral rights to the odd-numbered (square-mile) sections of land in this area, while retaining the even-numbered sections as federal property.1 Thus, four private (railroad) sections surrounded each federal section and four federal

The "Cowboyification" of Wyoming Agriculture

In the 1947 film, Angel and the Badman, Dr. Mangram (played by Tim Powers) says to a farmer's wife, Mrs. Russell (bit player), This isn't civilized Pennsylvania, this is the raw frontier?this is a place where mayhem, theft and murder are the commonplace instead of the usual. The portrayal of the range-cattle industry in nineteenth-century Wyoming reinforced this image. Cattlemen eliminated rustlers, even hired killers such as Tom Horn, and fought sheepmen for control of the range, then turned their aggression against farmer/settlers. In the classic western, Shane, for example, the setting is central Wyoming where Jack Schaefer's protagonist confronts the grasping rancher, Ryker, and his hired gunslinger, Wilson. It sharply draws the line between good and evil, the civilized farmer and the primitive rancher. The sod-busters are no match for Ryker's power and strong-arm tactics, as Wilson proves when he murders one of the farmers. Shane confronts Wilson and Ryker in the local saloon, and says to Ryker, Your kinda days are over. After Shane's revenge by gunning down Wilson and Ryker, Shane rides off into the mountains taking his aura of violence with him, and one assumes that the vindicated farmers will prosper unmolested by the cattlemen.1

Morphology of the Casper Mountain uplift and related, subsidiary structures, central Wyoming: Implications for Laramide kinematics, dynamics, and crustal inheritance

The general east-west trend of the regional-scale, fault-related Cas per Mountain uplift in central Wyoming reflects a preexisting Pre cambrian fabric along which there was Laramide compressional re activation. Initial fault displacement on the south-dipping Casper Mountain fault zone probably predates displacement on the inter secting, northwest-trending, northeast-dipping Casper arch thrust that forms the northeastern border of the Wind River basin. Later phase, incremental, Laramide displacements occurred along both fault zones: left-oblique slip on the Casper Mountain fault zone, dip slip on the crosscutting Casper arch thrust. Basement-involved thrust generation of the subsidiary Laramide, northwest-trending Iron Creek and Emigrant Gap anticlines along the north (footwall) side of the Casper Mountain fault zone also occurred during this later phase Laramide deformation. Perturbation of far-field, northeast-southwest, Laramide max imum horizontal paleostress trajectories (s1) to local, nearly fault-normal orientation at Casper Mountain, together with strain par titioning, is proposed to explain the apparent coeval development of divergent hanging-wall and footwall, basement-involved, fault-related structures. This kinematic and dynamic interpretation may be applied conditionally to other east-west-trending Laramide up lifts in the central Rocky Mountain foreland province.

Calcite cement distribution and its effect on fluid flow in a deltaic sandstone, Frontier Formation, Wyoming

Precipitation of extensive calcite cement during burial diagenesis can strongly modify the depositional permeability of a sandstone reservoir and affect fluid flow during production. To predict subsurface flow through cemented reservoirs, permeability distributions used in fluid-flow models must reflect this diagenetic overprint. Calcite cements in sandstones commonly occur as irregularly distributed concretions, which makes it difficult to predict diagenetic permeability modifications in the subsurface from typically spaced wells. Outcrops can provide a continuous image of heterogeneity produced by concretionary calcite cements. The size and distribution of calcite concretions were mapped in outcrops of the Frewens sandstone, Frontier Formation, in central Wyoming. Large, tabular calcite concretions in this deltaic sandstone generally follow basinward-inclined bedding. Median thickness of the concretions is 0.6 m, length is 4.2 m, and width is 5.3 m. The highest cement fraction is in the high-permeability facies at the top of the sandstone body. Concretion centers are approximately Poisson distributed within the sandstone. The upward-increasing cement fraction is caused by upward-increasing concretion size. Lateral variation in the fraction of the sandstone cemented by calcite has a normal distribution, with a mean of 12% (s = 5%). Spatial distribution of calcite cement in the Frewens sandstone was modeled using indicator geostatistics. Variograms were inferred from outcrop maps of cement. Indicator semivariograms of cement have a range of 30 m horizontally and 2.5 m vertically, dimensions that correspond approximately to the size of the largest concretions. Stochastic images of cement were created using indicator simulation with vertically varying cement proportion. Flow models indicate that concretions make flow paths more tortuous and retard flow in the coarser facies near the top of the sandstone. The fastest path through the sandstone is in the lightly cemented, high net-to-gross center of the sandstone body. Because the cement mainly occurs within the highest permeability facies in the sandstone body, a model based on depositional facies alone would overestimate upscaled permeability of the Frewens sandstone.

Lowstand deltas in the Frontier Formation, Powder River basin, Wyoming: Implications for sequence stratigraphic models

Deposits of lowstand deltas formed on the floor of the Cretaceous Interior seaway of North America are found in the Cenomanian, lower Belle Fourche Member of the Frontier Formation, central Wyoming. Sandstones located in similar distal basin locations, hundreds of kilometers basinward of highstand shoreline deposits, form important hydrocarbon reservoirs isolated within marine shales, but interpretation of their origin has been highly controversial. The distribution, geometry, and internal facies of these sandstones are documented by an extensive outcrop study and regional subsurface correlations to develop genetic facies models for these deposits. This integrated record of lithofacies, ichnofacies, palynofacies, paleocurrent data, bedding relationships, and isolith maps incorporates observations from nearly 100 measured outcrop sections and about 550 subsurface well logs. Four episodes of sediment progradation and subsequent transgression each left behind gradually upward-coarsening deltaic sandstones that have eroded tops. These deltaic sandstones have a lobate to elongate geometry, basinward-dipping internal clinoform bedding, radiating paleocurrents, a low to moderate degree of shallow-marine burrowing, and show variable wave influence and tidal influence on deposition. Delta plain, paralic, and nonmarine facies have been eroded from the top of deltaic successions. Erosion surfaces capping progradational deltaic successions are the only stratal discontinuities that can be mapped regionally, and they appear to record transgressive ravinement enhanced over areas of structural uplift, compared with lowstand surfaces of erosion, which record the bypass of sediments basinward. Low accommodation during lowstands left little room for sandstones to stack vertically, and successive episodes of delta progradation were offset along strike. More tide-influenced delta deposits formed within shoreline embayments (Begin page 262) defined by the topography of older wave-influenced delta lobes and subtle syndepositional deformation of the basin floor. Standard sequence stratigraphic terminology is difficult to use in broad lowstand systems like the Frontier Formation because sandstones do not show simple vertical stacking patterns, major stratal discontinuities can form by processes other than lowstand fluvial erosion, and minor syndepositional deformation of the basin floor exerts a first-order influence on depositional and sediment preservation patterns. Although many basin-distal sandstones have been interpreted to be deposits of offshore bars, shelf-isolated valley fills, and stranded shorelines, the Frontier Formation examples documented here suggest that many of these deposits may be top-eroded deltas formed where rivers delivered sediment to lowstand coastlines. The external geometry and internal heterogeneities of hydrocarbon reservoirs found in these types of deposits reflect processes active on the low accommodation deltaic shoreline, even in cases where subsequent ravinement has significantly truncated the deposits during transgression.

Food Habits of Northern Goshawks Nesting In South Central Wyoming

Northern Goshawks (Accipiter gentiles) nesting in south central Wyoming consumed at least 33 species of prey; 14 were mammals and 19 were birds. Based on percent occurrence in regurgitated pellets, dominant (>10% frequency) prey species included: red squirrel (Tamiasciurus hudsonicus; present in 50% of pellets), Northern Flicker (Colaptes auratus; 34%), American Robin (Turdus migratorius; 30%), golden-mantled ground squirrel (Spermophilus lateralis; 27%), and Uinta or least chipmunk (Tamias spp.; 10%). Woodpeckers [combined frequency of occurrence for Northern Flicker, Red-naped Sapsucker (Sphyrapicus nuchalis), Hairy Woodpecker (Picoides villosus), Three-toed Woodpecker (Picoides tridactylus), and unknown species] were present in 52% of pellets. Unusual food items in the diet included mule deer (Odocoileus hemionus) and American marten (Martes americana).

Cave Gulch 3-D Survey, Wind River Basin, Wyoming: A major gas discovery developed using poststack depth migration

Waltman Arch, a transbasinal arch that trends northward across the Wind River Basin of central Wyoming, is overridden by the Owl Creek Thrust at its northern terminus (Figures 1 and 2). Fields along Waltman Arch produce from multiple stacked sandstone pays in the Fort Union, Lance, Meeteetse, Mesa Verde, Frontier, Muddy, and Lakota Formations (Figures 3 and 4). To the northwest, in Madden Field, there is excellent production from deeper Madison carbonates.

Quantitative Outcrop Data for Flow Simulation

ABSTRACT An architectural analysis documents variations in bedding geometry and rock properties within a tide-influenced deltaic sandstone exposed in the Cretaceous Frontier Formation of central Wyoming, USA. Digital maps of bedding, lithofacies, and diagenetic cements, as well as vertical logs of grain size, lithofacies, and permeability, describe rock properties that potentially influence fluid flow behavior. These records are used to construct simulation models that assess the relative importance of different types of geologic variability on prediction of subsurface fluid flow. Two 25-meter-thick tide-influenced deltaic sandstone bodies coarsen upward and contain inclined beds that reflect episodic delta-front progradation. Decimeters- to meters-thick beds within bodies alternate between cross-stratified sandstones formed during rapid flows and shales deposited during more quiescent conditions. Down depositional dip, bed-draping shales are more continuous and lithofacies within sandstone beds become finer-grained and increasingly heterolithic. As sandstone beds fine down dip, mean permeability values decrease and coefficients of variation increase, permeability values change from nearly normal distributions to highly right-skewed, and permeability values become more strongly spatially correlated. Nodular cements also affect permeability. All of these variations were modeled using stratigraphic cornerpoint grids that preserve stratal geometry and gridblocks with properties assigned using a combination of rock property maps and statistical models based on rock property logs. Simulations predict effects on fluid flow of geologic heterogeneity at different scales, the influences of process variables, and the effects of different methods of grid construction and rock property assignment. Flow simulations of water flooding through a 22 m thick by 360 m long segment of a deltaic sandstone oil reservoir predict that: (1) rapid flow through coarser-grained deposits at the top of the sandstone body tends to draw water upward; (2) thin shales draping sandstone beds shunt downdip-directed flow downward and updip-directed flow upward; (3) cement nodules cause more tortuous flow patterns but have little effect on recovery efficiency; (4) Methods of predicting intrafacies correlation of permeability have little effect on flow behavior at this scale. A simulation model constructed using a high-resolution Cartesian grid did not resolve the effects of inclined shales, demonstrating the usefulness of stratigraphic cornerpoint grids for modeling flow through complex geologic deposits. Flow simulations of tracer flow through a meter-thick cross-stratified bed within the deltaic sandstone body showed that at this scale shale drapes and models of the intrafacies distribution of permeability have statistically significant effects.

Multi-component seismic surveying for near surface investigations: examples from central Wyoming and southern England

Within the crust, the weathered layer has been shown to contain some of the greatest values of shear wave velocity anisotropy. There are two main causes of this shear wave velocity anisotropy. In all rock types, anisotropy results from structural weaknesses commonly manifest as aligned open fractures. In sedimentary rocks, additional anisotropy can result from mineral or grain particle alignment and layering or bedding. Unconsolidated sediments also show this preferential particle alignment which causes ordered heterogeneity or anisotropy that can be described as transverse isotropy. Both forms of anisotropy can have significant implications not only for the strength of a material but also for the passage of fluids through it. Two case histories are presented that describe these forms of anisotropy in the near surface and the implications for environmental investigations. In central Wyoming, a downhole survey was conducted using 28 borehole locations instrumented with three-component (3C) receivers and surface shear wave impact sources. The sandstone bedrock at the site showed anomalous areas of high shear wave anisotropy that were interpreted to be due to a dominant regional fracture pattern. In southern England, a downhole survey was conducted in two boreholes using an array of 3C receivers and both surface and down hole shear wave sources. At this site, the heavily overconsolidated Oxford Clay showed transverse isotropy due to the strong preferential particle alignment. Both examples illustrate the use of shear wave seismic studies for mapping near surface geological features that may have important impacts for environmental and hydrogeological investigations.

Aeolian sediments in lower to middle (?) Triassic rocks of central Wyoming

The Lower to Middle(?) Triassic Red Peak and Crow Mountain Formations of central Wyoming have commonly been interpreted as being of shallow marine or shelf origin. This paper presents conclusive evidence of an aeolian origin for parts of the two formations. The interpretation is based on highly indicative sedimentary structures including wind ripple, grainfall and grainflow strata, lag deposits, and granule ripples in the sediments of these formations. Facies in the upper Red Peak and lower Crow Mountain Formations represent aeolian dune, sandsheet, wet interdune and sabkha environments. Emphasis is placed on the recognition and interpretation of correlative surfaces of regional extent, which not only allow subdivision of the aeolian sediments into different genetic sequences, but also aid in the reconstruction of the depositional history. The recognition of an aeolian deposystem and of regional bounding surfaces adds valuable information to the efforts of reconstructing the Triassic paleogeography of the Western Interior.

Combining Outcrop Data and Three-Dimensional Structural Models to Characterize Fractured Reservoirs: An Example from Wyoming

Combining a detailed outcrop characterization of fracture and fault occurrence with attributes from a three-dimensional model of an anticlinally folded clastic reservoir body, we determine which characteristics of the structural form and evolution are most closely related to the development of important reservoir-scale structures. Our example reservoir body studied is the Frontier Formation 1 sandstone in Oil Mountain, an asymmetric anticline on the western flank of Casper arch in central Wyoming. The three-dimensional model of the structure was constructed using an iterative scheme designed to maximize interpretation accuracy and precision. The model was analyzed to determine the spatial variance in morphologic and kinematic attributes. Using a quantitative testing approach, we found that the intensity of tectonically produced fractures is closely related spatially to rate of dip change and total curvature, with the former having the strongest correlation. This folding is a low-strain process compared to tear faulting, which has the strongest spatial correlation to larger strains. The location and magnitude of these higher strain areas can be adequately predicted by three-dimensional restoration and forward modeling of the upper bounding surface of the reservoir body. We use these results to build a predictive model for fault and fracture distribution at Oil Mountain and to discuss how this approach can aid in the exploitation of analogous producing reservoirs.

A Method to Estimate Length Distributions from Outcrop Data

Dimensions of shales and other geologic bodies that affect fluid flow through reservoirs and aquifers are often estimated from analogous deposits exposed in outcrops. Shale lengths observed in outcrops are biased because the finite length of outcrops truncates longer shales and long shales tend to be overrepresented in the sample. Shale length distributions can be modeled using an Erlangian probability density function based on termination frequency. Termination frequency can be calculated from outcrop observations even if the shales are incompletely exposed. Termination frequency is unbiased regardless of underlying shale length distribution and outcrop size and shape. Complex length distributions can be represented by a weighted sum of Erlangian models, each with a distinct termination frequency. The proportions and termination frequencies of the component models can be estimated using Bayes' theorem. Subsamples of the outcrop area can be analyzed to quantify spatial trends in termination frequency and thus shale length. These methods can be applied to estimate length distributions of any geologic object exposed in outcrops or other spatially limited samples. In many cases estimated termination frequency is normally distributed, and its variance can be estimated using closed-form expressions. Shale length distributions for the Frewens Sandstone were modeled using one- and two-component Erlangian probability density functions. The Frewens Sandstone is a tide-influenced deltaic sandstone body within the Cretaceous-age Frontier Formation, exposed in central Wyoming, USA. Length observations and Erlangian models agree reasonably well. Because the models correct for the effects of shale truncation in limited outcrop exposures, predicted means and proportions of long shales are substantially greater than observed values. There is a vertical trend and pronounced vertical cyclicity in termination frequency, indicating that shales become shorter upward and intervals of longer and shorter shales alternate. Along strike, termination frequency decreases away from the sandstone-body axis, reflecting greater preserved shale lengths toward sandstone-body margins. No correlation was observed between distance along dip and termination frequency. Termination frequencies and histograms of shale length for adjacent, perpendicular walls are similar, indicating that there is no anisotropy in shale length.

Revision of the Wind River faunas, Early Eocene of central Wyoming. Part 14. Postcranium of Shoshonius cooperi (Mammalia: Primates)

Revision of the Wind River faunas, Early Eocene of central Wyoming. Part 14. Postcranium of Shoshonius cooperi (Mammalia: Primates)

Architecture of a tide‐influenced river delta in the Frontier Formation of central Wyoming, USA

The Frewens sandstone is composed of two elongate tide‐influenced sandstone bodies that are positioned directly above and slightly landward of a more wave‐influenced lobate sandstone. The 20‐km‐long, 3‐km‐wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre‐thick heterolithic cross‐strata and, finally, to metres‐thick sandstone‐dominated cross‐strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb‐dominated and nearly parallel the trend of sandstone‐body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large‐scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone‐dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100‐metre‐wide lenses that shingle off the sandstone‐body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide‐influenced river delta. Metres‐thick cross‐strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened.

A METHOD FOR DETECTING DEW A TERING EFFECTS OF UNDERGROUND MINING ACTIVITIES ON SURF ACE WETLANDS

In 1996 US Energy/Kennecott Uranium Company initiated a large-scale, long-term monitoring program to document whether or not proposed uranium mining activities under Green Mountain in Central Wyoming would cause a groundwater draw-down resulting in changes in the existing riparian/wetland habitats. The monitoring program consisted of establishing 12 study drainages on Green Mountain and six control drainages on an adjacent but hydrologically isolated mountain not scheduled for mining. Baseline data were collected in 1996 and 1997 prior to the commencement of mining. For each drainage, breeding bird densities (birds/km) and richness (species/km), winter wild ungulate fecal pellet group densities (groups/km), small mammal densities (captures/trap night), and density and species composition of aquatic macro invertebrates were measured along permanent, marked transects within each riparian zone. In order to characterize the baseline vegetation and isolate the effects of livestock grazing, species composition, percent cover, production, and type boundary delineation of riparian vegetation were quantified within adjacent fenced and unfenced half-acre sample sites within each drainage. Baseline photographs were taken at permanent marked points from fixed angles at each of the sample sites. Piezometer holes were drilled at each monitoring site for measuring potential changes in ground water levels over time. If, during mining,more » water levels are found to drop significantly from baseline, a new study of wildlife and vegetative parameters would be conducted to determine whether or not significant decreases in wetland function or changes from baseline characteristics have occurred.« less

Abstract: Geology of the Cloud Creek Impact Structure on the Casper Arch, Central Wyoming 

Abstract: Geology of the Cloud Creek Impact Structure on the Casper Arch, Central Wyoming