Mountain Bighorn Research Articles

Spectral Stratigraphy: Multispectral Remote Sensing as a Stratigraphic Tool, Wind River/Big Horn Basin, Wyoming: ABSTRACT

Stratigraphic and structural analyses of the Wind River and Big Horn basins areas of central Wyoming are in progress. One result has been the development of a new approach to stratigraphic and structural analysis that uses photogeologic and spectral interpretation of multispectral image data to remotely characterize the attitude, thickness, and lithology of strata. New multispectral systems that have only been available since 1982 are used with topographic data to map upper paleozoic and Mesozoic strata exposed on the southern margin of the Bighorn Mountains. Thematic Mapper (TM) satellite data together with topographic data are used to map lithologic contacts, measure dip and strike, and develop a stratigraphic column that is correlated with conventional surface and subsurface sections. Aircraft-acquired Airborne Imaging Spectrometer and Thermal Infrared Multispectral Scanner data add mineralogical information to the TM column, including the stratigraphic distribution of quartz, calcite, dolomite, montmorillonite, and gypsum. Results illustrate an approach that has general applicability in other geologic investigations that could benefit from remotely acquired information about areal variations in attitude, sequence, thickness, and lithology of strata exposed at the Earth's surface. Application of their methods elsewhere is limited primarily by availability of multispectral and topographic data and quality of bedrockmore » exposures.« less

Characteristics of a Hunted Mountain Lion Population in Wyoming

Population characteristics were estimated from June 1981 to July 1983 for a hunted mountain lion (Felis concolor) population occupying a 741-km2 study area in the Big Horn Mountains, Wyoming. Based on the capture-recapture of 46 lions and radio-telemetry, snow-tracking, and harvest data, winter population densities were estimated at 29 km2/lion (1981-82) and 22 km2/lion (1982-83). Sex ratios of 28 kittens and 22 adults did not differ (P > 0.05) from equality. Kittens, born primarily in autumn, comprised about 50% of the population each winter, and 11 postnatal litters averaged 2.7 kittens. Some juveniles dispersed at about 12-15 months of age; 5 were recovered 9-274 km from their natal areas. Two resident females bred at 13and 19-month intervals. The age structure of both sexes was young, the oldest adult being about 7 years old. Observed mortality the 1st year was 27% of the total population and 0% the 2nd year; immigration apparently compensated for mortalities. Home areas of 4 resident females averaged 67 km2 and overlapped almost completely. Those of the 2 resident males overlapped slightly and averaged 320 km2. Male home areas overlapped several female home areas. J. WILDL. MANAGE. 50(4):648-654 Characteristics of unhunted mountain lion populations have been reported in California (Sitton and Weaver 1977; Hopkins et al., in press) and Utah (Hemker et al. 1984). A lightly hunted lion population was described in Idaho (Hornocker 1969, 1970; Seidensticker et al. 1973), and relatively heavily hunted populations were described in Arizona (Shaw 1977), Colorado (Currier et al. 1977), and Nevada (Ashman et al. 1983). This paper reports characteristics of a hunted lion population in the Big Horn Mountains, Wyoming, from June 1981 to July 1983. Impetus for this study was provided by the lack of detailed biological data on lions in Wyoming; information previously was limited to general status reports. Day and Nelson (1929, cited in Nowak 1976) reported that the species was very scarce, and Young (1946) said it was confined mainly to the western mountains. Long (1965:705) believed the lion was nearly extirpated by the early 1960's. Roop (1971) indicated that lions were scarce and restricted to relatively inaccessible areas. Berg et al. (1983) conducted a mail survey in Wyoming and concluded the state's lion population was stable or had increased during the last 10 years, particularly in the Big Horn Mountains. Long-term resident ranchers and trappers in our study area corroborated this apparent, recent increase in mountain lions. This study was funded by the Wyo. Coop. Fish. and Wildl. Res. Unit and the Wyo. Game and Fish Dep. The Sheridan Work Unit of the U.S. Fish and Wildl. Serv. provided radio-telemetry equipment. Assistance also was provided by the Univ. Wyoming, the U.S. Bur. Land Manage., and the U.S. For. Serv. M. E. Bush, J. Hyde, and J. Childs assisted in a variety of important ways. We also are grateful to C. M. Gillin and H. L. Osborn, our technicians, and to the private landowners who cooperated with us during this study. S. H. Anderson, W. G. Hepworth, E. T. Thorne, T. J. Killough, and R. L. Phillips provided valuable support. We thank M. L. David for typing the manuscript.

Evidence that the Crystalline Cores of Uplifts Adjacent to the Powder River Basin Were Breached During Paleocene Time

Sandstones in the upper part of the Paleocene Tongue River Member of the Fort Union Formation in the Powder River basin are dominantly sublitharenite. These rocks contain abundant rock fragments of non-ferroan calcite, dolomite, chert, and foliated tine-grained metamorphic rock (phyllite). The carbonate and chert rock fragments were probably eroded from Paleozoic carbonate sequences flanking the Bighorn Mountains or the Black Hills. The phyllffic rock fragments indicate that the crystalline cores of these uplifts were exposed during Paleocene time, which is earlier during the Laramide Orogeny than has been previously demonstrated.

Phosphoria Reservoir Facies Exposed in the Northeast Bighorn Basin--An Exhumed Cottonwood Creek Oil Field?: ABSTRACT

Detailed stratigraphic correlations between well-exposed outcrops and nearby oil wells permit the delineation of porous carbonate reservoir facies within the Phosphoria Formation (Guadalupian) in the northeastern part of the Bighorn basin. The most significant petroleum reservoirs in this area occur in two depositional facies defined by faunas and vertical sequences of sedimentary and biogenic structures. Effective porosity development in the peritidal facies occurs in intraclast-pellet, dolomite packstone/grainstone, and irregularly laminated, fenestral algal-boundstone. In the restricted-marine facies, reservoir development occurred in bioturbated, dolomite mudstone-wackestone, and phylloid-algal and mollusk dolomite wackestone-packstone. Based on regional analysis, fenestral algal-boundstone pods are thought to have evolved as peninsula-island complexes paralleling reactivated northwest-southeast-trending faults on the east side of the Bighorn basin. In the northeastern Bighorn basin, peninsula-island complexes accumulated on the Bighorn and Sheep Mountain paleohighs. They defined an embayment in which restricted marine rocks were deposited. Porous peritidal rocks appear to have been concentrated along the seaward flanks of the thickest algal-boundstone pods, which grade laterally into porous restricted-marine lithologies. The geologic setting of exposed peritidal and restricted-marine reservoirs in the northeastern Bighorn basin appears to be similar to that of Cottonwood Creek field. An understanding of facies relationships may be useful in themore » further development of Cottonwood Creek field and for exploration for similar types of carbonate stratigraphic traps along the eastern margin of the Bighorn basin.« less

Nature of Thrusting Along Western Flank of Bighorn Mountains, Wyoming: ABSTRACT

Nature of Thrusting Along Western Flank of Bighorn Mountains, Wyoming: ABSTRACT

Two New Species of Cymopterus (Umbelliferae) from Western North America

Two species ofCymopterus are described as new:Cymopterus douglassi from the Lost River and Lemhi ranges of central Idaho and the closely relatedC. williamsii from the southern half of the Big Horn Mountains, Wyoming. Both are diploid on the basex=11 and occur on calcareous or dolomitic substrates. The mature fruit ofCymopterus williamsii differ from those ofC. douglassii in the absence of a functioning carpophore and in having 1, not 3–5 oil tubes in the intervals. Both species are unusual in the genus, though not unique, in that the dorsal ribs of the mericarps are not winged.

Origin of Shape Changes of Sand and Silt in a High-Gradient Stream System

ABSTRACT Changes in shape of sand and silt in streams may be a reflection of changes in source rock rather than the progressive effects of transport. If so, shape characteristics should change as the stream crosses geologic contacts. To clarify the problem, stream sediment samples were collected in two drainage basins on the west flank of the Bighorn Mountains, Wyoming. Three size fractions--fine sand, very fine sand, and coarse silt--were studied, using Fourier analysis and the scanning electron microscope. Provenance discrimination improves with increasing grain size. In all three size ranges sediment derived from a glaciated crystalline rock source can be differentiated from that derived from sedimentary rock sources. Sand from sedimentary rock sources can be subdivided into shape families according to the extent of diagenesis. In very fine sand and fine sand, sediment from the Flathead Sandstone is distinguishable from that derived from other sedimentary rocks. In fine sand the Tensleep and Darwin sandstones are also distinguishable as separate sources. Along Tensleep Creek, changes in the shape composition of sediment occur rather continuously due to transport of sediment by past glacial processes. Along Paintrock Creek, however, shape proportions do not change in a continuous manner but instead change by abrupt, discrete jumps which occur where additional sources provide sediment. The shape changes are due to the dilution of upstream sediment by sediment from adjacent sources. This suggests that downstream sources provide sediment at a greater rate than the upstream sources even though the gradient decreases with distance. This can be explained by the fact that the younger, downstream sedimentary rocks are more friable than the upstream rocks.

Seismic Exploration for Oil and Gas Traps in Wind River Basin: a Laramide Example: ABSTRACT

The Wind River basin in central Wyoming is typical of the large sedimentary and structural basins that formed in the Rocky Mountain region during Laramide deformation in latest Cretaceous and early Tertiary times. Northeast-southwest-oriented seismic profiles across the Wind River basin and flanking Owl Creek and Bighorn Mountains illustrate the structural configuration and correspondent stratigraphic development of a typical Laramide intermontane basin. Understanding the geometry of the basin margin and the timing of structural movement aids in prospecting for mountain-front subthrust structures, like Tepee Flats field, and stratigraphic traps, like Haybarn field, in fluvial and lacustrine basin-fill sequences. The Wind River basin is structurally asymmetric with the basin axis close to the Owl Creek Mountains and Casper Arch thrusts, which form the north and east basin boundaries. Major Laramide deformation began in latest Cretaceous time (beginning of Lance Formation deposition) with pronounced downwarping of the basin trough and broad doming of parts of the peripheral areas. The intensity of movement increased through the Paleocene and culminated in early Eocene time as high mountains were uplifted along thrust faults. Clastic debris, stripped from the surrounding rising mountain arches, was shed basinward, resulting in a pronounced wedge-shaped accumulation of fluvial and lacustrine sediments now representing the Lance, Fort Union, Indian Meadows, and Wind River Formations. End_of_Article - Last_Page 862------------

Stratigraphy, Petrography, and Paleoenvironmental Interpretation of Mississippian-Pennsylvanian Amsden Formation South of La Barge Guard Station, Salt River Range, Western Wyoming: ABSTRACT

The Amsden Formation, named by N. H. Darton in 1904 during mapping of the Bighorn Mountains, Wyoming, consists of red shales, limestones, sandstones, and cherty beds. The Amsden was later subdivided into four members (in ascending order): the Darwin Sandstone (E. Blackwelder, 1918), the Horseshoe Shale (W. W. Mallory, 1967), the Moffat Trail Limestone (W. J. Sando and others, 1975), and the Ranchester Limestone (W. W. Mallory, 1967). All members crop out in the study area. The Darwin Sandstone Member is up to 88.4 m (290 ft) thick, disconformably overlies the Mississippian Mission Canyon Limestone, and is conformably overlain by the Horseshoe Shale Member. It is a quartzarenite with minor amounts of feldspar interpreted as being deposited in a nearshore or beach environment. The Horseshoe Shale Member is 25.9 m (85 ft) thick and conformably overlies the Darwin Member. The Horseshoe Shale Member contains fine-grained terrigenous sediment interpreted to have accumulated in a lagoon or back-reef environment. The lower part is a white to red siltstone with localized areas of pisolitic hematite; the upper part is organic-rich black shale containing palynomorphs. The Moffat Trail Limestone Member is 29.0 m (95 ft) thick and conformably overlies the Horseshoe Shale Member. The Moffat Trail consists of biomicrites, pelmicrites, and silty micrites. It is interpreted to represent open-marine, low-energy carbonate-shelf deposition. The Ranchester Limestone Member is 9.4 m (31 ft) thick and conformably overlies the Moffat Trail Member. The Ranchester contains silty dolomite, carbonate, and red siltstone, representing the maximum transgression of the Pennsylvanian sea. The Pennsylvanian Wells Formation conformably overlies the Ranchester Member. End_of_Article - Last_Page 932------------

Lacustrine Deposits in the Paleocene Fort Union Formation, Northern Bighorn Basin, Montana

ABSTRACT The Fort Union Formation of the northern Bighorn Basin is a complex sequence of interbedded fluvial, lacustrine, and palustrine deposits. A probable lacustrine facies is well developed near the center of the basin. These Tiffanian-age sediments, here designated the Belfry Member, consist of thin, laterally persistent beds of fine-grained lenticular and tabular sandstones, shale and mudstones, lignite, and argillaceous or fossiliferous limestone. In general, their lithologic characteristics, particularly the abundance of sandstones, are very different from those normally associated with lacustrine sequences, and may be misinterpreted as fluvial deposits. Two sections (Cody Road and Silvertip) were examined in detail. Sandstones are generally carbonate-cemented phyllarenites. Compositional differences exist between the two sections, with Silvertip having better textural maturity and more chert. Most limestones are argillaceous micrites, but biomicrudites are found in the upper Silvertip section. Mudstones and shales contain smectite, interstratified smectite-vermiculite, kaolinire, illite, and chlorite separable into 4 major assemblages. These alternate irregularly throughout the sections, but assemblages without an expandable clay occur only in the upper part of Silvertip. The Belfry lakes were apparently shallow and of limited areal extent, with fluctuating water levels and low-energy, muddy shorelines. Clastic input from the rising Beartooth and Bighorn mountains was high, but composition of carbonates and clays suggests that the lake waters were alkaline, slightly saline, with generally sluggish circulation and mildly reducing bottom conditions.

Stratigraphy and Depositional Environment of Middle Member of Minnelusa Formation, Central Powder River Basin, Wyoming: ABSTRACT

Abstract Regional correlations, from the southern to northern Black Hills and across the central Powder River Basin to the Bighorn Mountains, serve as the framework for a depositional model of Middle Minnelusa sediments. In the eastern part of the study area, deposition took place in a carbonate sabkha environment. During transgressive periods most of this region was covered by a restricted, shallow sea. In the northern Black Hills, close to the limit of the transgression, deposition occurred in a coastal dune setting. During regressions, the sabkha prograded westward toward the Lusk Embayment. Coastal dune-fields to the north and isolated dune complexes to the south migrated southwestward across this prograding sabkha. West of the Lusk Embayment, deposition occurred in a sand-dominated tidal flat environment during transgressions and along the coastal edge of an eolian sand sea during regression.

Introduction to Stratigraphy, Structure, and Geologic Problems in Big Horn Basin, Wyoming and Montana: ABSTRACT

End_Page 1342------------------------------As the cumulative production of oil from the Big Horn basin approaches the 2 billion bbl mark, it is appropriate that we look at the geology once again. The Big Horn basin, located in northwestern Wyoming and south-central Montana, is bordered on the east by the Big Horn Mountains; on the south by the Owl Creek Mountains; on the west by the Absaroka and Beartooth Mountains; and on the north by the Nye-Bowler lineament. The combination of a great reservoir-source duet in the Paleozoic rocks and the creation of large anticlines during the Laramide orogeny has been the key to the Big Horn basin's success as an oil producer. Stratigraphy of the Big Horn basin can be divided generally into (1) the Middle Cambrian clastics, (2) the Paleozoic shelf carbonates, (3) the Mesozoic clastics, (4) the Late Cretaceous to Tertiary synorogenic clastics, and (5) the Tertiary post-orogenic clastics and volcanics. By far the most economically important formations have been the Permian Phosphoria and Pennsylvanian Tensleep Formations. This dynamic duo consists of porous eolian and shallow marine, quartz sandstones of the Tensleep overlain by shallow marine, oil-rich carbonates of the Phosphoria. The two have combined to produce over 1.5 billion bbl of oil in the Big Horn basin alone. The draping of the Tensleep and Phosphoria over large Laramide structures (closures of over 5,000+ ft, 1,500 m, and areal extents up to 15 mi2, 40 km2) was the final key. An upcoming afternoon session of papers will explore the proposed anatomies and mechanisms of folding in the Cordilleran foreland. There is a controversy over the morphology of the folds in the foreland. Put simply, there is some disagreement over how much the horizontal or thrusting component contributes to these folds. Stearns, who described the fold at Rattlesnake Mountain in the 1971 Wyoming Geological Association guidebook, favors drape folding over near-vertical faults in the Precambrian. Berg in the 1962 AAPG Bulletin and Gries in the 1983 AAPG Bulletin favor a more thrusted model with reverse fault planes dipping 60° to 30°. Sales in the 1968 AAPG Bulletin agrees with the morphology of Berg and Gries, but feels that the folds in the foreland were generated by faults with strong lateral components. Concerning other problems, Stone in the October 1967 AAPG Bulletin pointed out that the Paleozoic reservoirs often have a common oil-water contact (OWC) within individual structures. He attributed the common OWC to fractures joining the reservoirs. The OWC is commonly tilted; this he attributed to hydrodynamic flow. An understanding of fractures and tilted oil-water contacts is imperative for successful exploration and production programs in the Big Horn basin. End_of_Article - Last_Page 1343------------

Mid-Cretaceous Biostratigraphic Units, Unconformities, and Diastrophism in Wyoming, Colorado, and Adjacent Areas: ABSTRACT

In the central Rocky Mountains and adjoining Great Plains, lithologies and hiatuses within sequences of mid-Cretaceous formations reflect widespread fluctuations of sea level and intermittent tectonism during Cenomanian, Turonian, and Coniacian time (88 to 96 m.y.B.P.). Siliciclastic and carbonate strata of marine origin in the Graneros, Belle Fourche, Greenhorn, Carlile, and Niobrara Formations grade laterally into marine and nonmarine siliciclastic beds of the Frontier Formation. The clastic strata are products of uplift and erosion in both the Sevier orogenic belt of Utah, Idaho, and western Montana, and a contiguous region within Utah, Colorado, Wyoming, Montana, and Nebraska. The ages of these rocks, the durations of intervening hiatuses, and the times of diastrophis were determined mainly from a detailed succession of marine molluscan index fossils. Outcrops at scattered localities in this region, in a western part of the Cretaceous seaway, as well as outcrops in eastern South Dakota and northwestern Iowa, near the eastern shore of the seaway, indicate a marine transgression in the Cenomanian and early Turonian (Belle Fourche and Greenhorn time), a marine regression in the middle Turonian (early Carlile time), and a marine transgression in the late Turonian and Coniacian (late Carlile and early Niobrara time). However, the stratigraphic record of these widespread events has been obscured in most of Wyoming and Colorado by submarine and subaerial erosion and attendant sedimentation associated with episodic orogenic activity during the Turonian and Coniacian (88 to 91 m.y.B.P.). In central and northwestern Wyoming, strata as young as late Cenomanian (early Greenhorn age) are disconformably overlain by beds of early middle Turonian (latest Greenhorn) age. Uplift and erosion in these areas probably occurred during early to earliest middle Turonian time. In western Colorado, early middle Turonian strata (Fairport Member of the Carlile) and older rocks are disconformably overlain by late middle Turonian strata (Blue Hill Member of the Carlile), indicating deformation and truncation in the middle Turonian. Moreover, truncated beds as young as late middle Turonian (Codell Sandstone Member of the Carlile) are overlain by early late Turonian strata (Juana Lopez Member of the Carlile) in Colorado and Wyoming, reflecting earliest late Turonian orogenic activity in the icinity of the Front Range, Laramie Range, and Bighorn Mountains. Some of the rocks of early late Turonian age (a lower part of the Wall Creek Member of the Frontier) were, in turn, uplifted and eroded during later late Turonian time in an area that extends from Yellowstone Park to central Wyoming. Furthermore, at outcrops near the Laramie Range, truncated beds of late Turonian age (Wall Creek Member of the Frontier) and the overlying Coniacian strata (basal Niobrara) indicate earliest Coniacian tectonism and erosion in southeastern Wyoming. Elongate areas of uplift and erosion and of discrete sedimentary facies of mid-cretaceous age commonly trend approximately southeastward and northeastward in the central Rocky Mountains-western Great Plains region. From Yellowstone Park southeast to the vicinity of Casper, Wyoming, intermittent truncation and deposition during the Turonian are especially evident. End_of_Article - Last_Page 513------------

Oil and Gas Prospecting Beneath Precambrian of Foreland Thrust Plates in Rocky Mountains

Only 16 wells in the Rocky Mountain region have drilled through Precambrian rocks to test the 3 to 6 million acres of sedimentary rocks that are concealed and virtually unexplored beneath mountain-front thrusts. One recent test is a major gas discovery, another a development oil well, and over half of the unsuccessful tests had oil or gas shows. These wells have not only set up an exciting play, they have also helped define the structural geometry of the mountain-front thrusts, including the angle of the thrust, the amount of horizontal displacement, and the presence or absence of fault slivers containing overturned Mesozoic or Paleozoic rocks. Important for further geophysical exploration, these wells have provided vital data on seismic velocities in Precambrian rocks. A alysis of these data has stimulated further exploration along the fronts already drilled: in Wyoming, the Emigrant Trail thrust, the Washakie thrust, the Wind River thrust, the thrust at the north end of the Laramie Range, and the Casper arch; in Utah and Colorado, the Uncompahgre and Uinta uplifts. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain-front thrust in the Rockies. An unsuccessful attempt to drill through the Arlington thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial arch in Colorado has not condemned that area; in fact, another well is being drilled at this time. Untested areas that will be explored in the near future are: in Wyoming, the south flank of the Owl Creek Range, the southwest flank of the Gros Ventre Range, the east and west flanks of the Big Horn Mountains, the west flank of the Big Horn basin, the north flank of the Hanna basin; in Utah, the south flank of the Uinta Mountains; and in Colorado, the White River uplift, the no th flank of North Park basin, and the Front Range.

Hydrocarbon Accumulation in Pennsylvanian-Age Ten Sleep Sandstone: The Trapper Creek Tar Sand Deposit, Big Horn Basin, Wyoming: ABSTRACT

Preliminary investigations indicate a potential tar sand accumulation in the Trapper Creek deposit of more than 2.13 million tons of mineralized material with a yield of 0.92 bbl per ton of 5.2° API oil for an approximate resource of 1.96 million bbl of recoverable petroleum. Remote sensing data suggest that the accumulation is in part controlled by two major and four minor lineaments which traverse the area. Stratigraphic and lithologic criteria can be used to infer a Minnelusa-type mode of occurrence. Ancillary stream sediment and outcrop geochemistry data yield locally anomalous but uneconomic concentrations of Mg, Ca, Ti, Mn, Ag, Cu, Mo, V, K, and Si, which may have significance in the identification of similar hydrocarbon accumulations along the west flank of th Bighorn Mountains. End_of_Article - Last_Page 419------------

Hydrocarbon Accumulation in Pennsylvanian-Age Tensleep Sandstone: Trapper Creek Deposit, Wyoming: ABSTRACT

Preliminary investigations indicate a potential hydrocarbon accumulation in the Trapper Creek, Wyoming, deposit of more than 2.13 million tons of mineralized material with a yield of 0.92 bbl per ton of 5.2° API oil for an approximate resource of 1.96 million bbl of recoverable petroleum. Remote sensing data suggest that the accumulation is in part controlled by two major and four minor lineaments which traverse the area. Stratigraphic and lithologic criteria can be used to infer a Minnelusa-type model of occurrence. Ancillary stream sediment and outcrop geochemistry yield locally anomalous, but uneconomic concentrations of magnesium, calcium, titanium, manganese, silver, copper, molybdenum, vanadium, potassium, and silicon, which may have significance in the ident fication of similar hydrocarbon accumulations along the west flank of the Bighorn Mountains. End_of_Article - Last_Page 1330------------

Potentiometric Surface and Quality of the Water of Madison Group, Montana: ABSTRACT

The potentiometric surface map of the Madison Group of Mississippian age in Montana indicates that water in this aquifer generally moves northward. The principal recharge areas of the Madison are the Little Belt and Big Snowy Mountains of central Montana, the Pryor and Bighorn Mountains of south-central Montana and northern Wyoming, and the Black Hills uplift of Wyoming and South Dakota. The dissolved-solids concentration of the water ranges from a few hundred milligrams per liter near mountainous recharge areas to about 300,000 mg/L in the End_Page 1336------------------------------ northeastern part of the state (Williston basin). The ratio of sodium plus potassium plus chloride to dissolved-solids concentration is greatest in northeastern Montana where the Madison contains salt beds, and decreases toward recharge areas. The ratio of sulfate to total anions is greatest in north-central and southeastern Montana where anhydrite probably is the source of the sulfate. The ratio is smallest in northeastern and northwestern Montana; however, the concentration of sulfate, in milligrams per liter, can be greater in northeastern Montana than in other areas because of the greater concentration of all dissolved solids. End_of_Article - Last_Page 1337------------

Trapper Canyon Deposit, Eastern Big Horn Basin, Wyoming: Tar Sand or Heavy Oil?: ABSTRACT

The Trapper Canyon Deposit (Battle Creek Deposit in U.S. Bureau of Mines Monograph 12) is located on the western flank of the Bighorn Mountains approximately 30 mi (48 km) east of Greybull, Wyoming. The petroleum occurs in the upper eolian sequence of the Pennsylvanian Tensleep Sandstone which dips from 5° to 8° to the southwest. The deposit was initially reported by N. H. Darton in U.S. Geological Survey Professional Paper 51 in 1906. A characterization study was made on the deposit which included mapping the deposit and surrounding area, measuring three stratigraphic sections in the Tensleep Sandstone, and sampling 13 outcrop localities. Thickness of the deposit ranged from 0 to 22.5 ft (6.8 m) in the 13 sample localities. Preliminary analyses of outcrop sampl s indicate API gravities and viscosities consistent with the definition of a tar sand. Oil properties are similar to those published for Phosphoria-sourced oils produced from the Tensleep Sandstone in fields to the west. Lateral pinch-out of the deposit, tight characteristics of upper and lower bounding units, and the lack of any apparent structural controls in the area, are all evidence for a stratigraphic trapping mechanism. Recoverable reserves are estimated at 1.96 million bbl over a 67-acre (27 ha.) area. End_of_Article - Last_Page 1359------------

Oil and Gas Prospecting Beneath Precambrian in Rocky Mountains: ABSTRACT

Although the Rocky Mountains have their first large sub-Precambrian hydrocarbon discovery, only 15 wells have been drilled through Precambrian to test the 3 to 6 million acres (1 to 2 million ha.) of sedimentary rocks that are concealed and virtually unexplored beneath mountain front thrusts. More than half of these wells had oil and gas shows and one was a producing development oil well. These wells have not only set up an exciting play for the future, they have also helped define the structural geometry of the mountain front thrusts of the Rocky Mountain foreland, including the angle of the thrust and the presence or absence of fault slivers of overturned Mesozoic or Paleozoic rocks. Most important for further geophysical exploration, these wells have provided vital dat on seismic velocities in Precambrian rocks. Analysis of these data will stimulate further exploration along the fronts already drilled: the Emigrant Trail thrust, the Washakie thrust, the Wind River thrust, the Uinta Mountain thrust, and the thrust at the north end of the Laramie Range. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain front thrust in the Rockies. Wells are presently being drilled on the Casper arch and the west flank of the Big Horn basin adjacent Oregon Basin field. An unsuccessful attempt to drill through the Arlington thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial arch in Colorado has not condemned that area. Untested areas that will be explored in the near future are: the south flank of the Owl Creek Range, the northeast flank of the Beartooth Mountains in Montana, the east and west flanks of the Big Horn Mountains, the north flank of the Hanna basin, the south flank of the Uinta Mountains, the White River uplift, the north flank of North Park basin, and the Front Range. End_of_Article - Last_Page 1180------------

Oil and Gas Prospecting Beneath the Precambrian of Foreland Thrust Plates in The Rocky Mountains

Only 15 wells in the Rocky Mountain region have drilled through Precambrian to test the 3-6 million acres of sedimentary rocks that are concealed and virtually unexplored beneath mountain front thrusts. More than half of these wells had oil and gas shows and one was a producing oil well. These wells have not only set up an exciting play for the future, they have also helped define the structural geometry of the mountain front thrusts, including the angle of the thrust and the presence or absence of fault slivers of overturned Meso­zoic or Paleozoic rocks. Most important for further geophysical exploration, these wells have provided vital data on seismic velocities in Precambrian rocks. Analysis of these data will stimulate further exploration along the fronts already drilled. the Emigrant Trail Thrust, the Washakie Thrust, the Wind River Thrust, the Uinta Mountain Thrust, and the thrust at the north end of the Laramie Range. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain front thrust in the Rockies. Wells are presently drilling on the Casper Arch and the west flank of the Big Horn Basin adjacent Oregon Basin Field. An unsuccessful attempt to drill through the Arlington Thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial Arch in Colorado has not condemned that area. Untested areas that will be explored in the near future are: the south flank of the Owl Creek Range, the northeast flank of the Beartooth Mountains in Montana, the east and west flanks of the Big Horn Mountains, the north flank of the Hanna Basin, the south flank of the Uinta Mountains, the White River Uplift, the north flank of North Park Basin, and the Front Range.