Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “The Mountain Geologist”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
USGS1981

Geologic controls of uranium mineralization in the Tallahassee Creek uranium district, Fremont County, Colorado.

Two important orebodies have been defined by drilling in the Tallahassee Creek uranium district, Fremont County, Colorado, namely the Hansen and the Picnic Tree. Host rocks are respectively the upper Eocene Echo park Alluvium, and the lower Oligocene Tallahassee Creek Conglomerate. Average ore grade is about 0.08% U3O8. The principal source rock is the lower Oligocene Wall Mountain Tuff. Leaching and transportation of the uranium occurred in alkaline oxidizing ground water that developed during alteration of the ash in a semi-arid environment. The uranium was transported in the groundwater and deposited in a reducing environment controlled by carbonaceous material and associated pyrite. Localization of the ore was controlled by groundwater flow conditions and by the distribution of organic matter in the host rock. -from Author

Mountain Geologist↗
USGS1985

Airfall tuff in the Browns Park Formation, northwestern Colorado and northeastern Utah.

Bedded airfall tuffs, mainly rhyolitic in composition and locally very thick, occur throughout the Browns Park Formation (upper Oligocene to upper Miocene) in northwestern Colorado and northeasternmost Utah. They have received only cursory attention other than for the purpose of radiometric dating. The present writer began study of the tuffs in 1980, hoping to use them as time-stratigraphic marker beds within the formation. Several tuff-rich stratigraphic sections were measured and numerous samples were collected. The results of petrographic and petrochemical studies of these samples are presented. -from Author

Mountain Geologist↗
USGS1980

Evaluation of organic matter, subsurface temperature and pressure with regard to gas generation in low-permeability Upper Cretaceous and Lower Tertiary sandstones in Pacific Creek area, Sublette and Sweetwater Counties, Wyoming.

The onset of overpressuring occurs at c.3,500 m, near the base of the U. Cretaceous Lance Formation. The development of overpressuring may involve several processes; however, interpretation of the available information indicates that active generation of large amounts of wet gas is one of the more important processes. The present minimum temperature at the top of overpressuring is at least 88oC. The preservation of abnormally high pressures is due to presently active generation of gas in a thick interval of discontinuous, very low-permeability shales, siltstones, and sandstones. - from Authors

Mountain Geologist↗
USGS1985

Description and origin of the lower part of the Mesaverde Group in Rifle Gap, Garfield County, Colorado.

Rifle Gap cuts through the central part of the Grand Hogback and the gap exposes the entire Upper Cretaceous Mesaverde Group. The best outcrops are on the roadcuts through the coal-rich lower part of the group. These roadcuts border the Rifle Gap dam and reservoir on the southwest, where the coal-rich section can be examined with little climbing away from the road. This coal-rich section consists of 1700 ft (518 m) of uppermost Mancos Shale, overlain by the Iles Formation and the lower part of the Williams Fork Formation of the Mesaverde Group. These formations are composed of members and informal units formed in a late Campanian coastal setting of deltas and intervening strandplains which supported vast peat swamps. The age and the coastal subenvironments of deposition of these units are indicated by fossils and sedimentary structures which can be studied on the roadcuts. The highest, most prominent roadcut exposes a thick, white sandstone called the Trout Creek Sandstone Member, Iles Formation, the correlations of which have been reassessed recently. This sandstone previously was correlated to a sandstone exposed at New Castle: the Rollins Sandstone Member, Mesaverde Formation, of the southern Piceance Creek basin. However, later field mapping showed that the two sandstones cannot be traced to each other but are separated by 310-450 ft (93.9-136.4 m) of strata along the central Grand Hogback. The recorrelations of the Trout Creek and adjacent sandstone members have influenced reconstruction of the local, late Campanian paleogeography of the oscillating shoreline. The sketches of paleogeographic reconstruction show an oscillating shoreline that trended northeast-southwest. This shoreline migrated inland to the area of Wolf Creek on the northern border of the Piceance Creek basin, and seaward only as far as the area of New Castle, until deposition of the Haas sandstone unit of the lower Williams Fork Formation. During the deposition of the Haas, the shoreline continued migrating seaward past New Castle. The general trend and seaward extent of this shoreline are based on regional correlations of ammonite zones and on local paleocurrent indicators from deposits of longshore drift and storm scour exposed in the central Grand Hogback. -Author

Mountain Geologist↗
USGS1985

Drainage development of the Green River Basin in southwestern Wyoming and its bearing on fish biogeography, neotectonics, and paleoclimates.

The Upper Green River flows southward out of the Green River Basin through a series of deep canyons across the Uinta Mountains in a course that post-dates the deposition of the Bishop Conglomerate (Oligocene). After the Eocene lakes disappeared, drainage was generally eastward across the present Continental Divide, until the Green River was captured near Green River, Wyo. by south-flowing drainage in middle Pleistocene time, ca., 600 kyr ago. Capture of the Upper Green River as recently as middle Pleistocene time, if a valid hypothesis, must take into account the marked differences between the endemic and indigenous fish fauna of the Green River and that of the North Platte. -from Author

Mountain Geologist↗
USGS1985

Mineral, chemical and textural relationships in rhythmic-bedded, hydrocarbon-productive chalk of the Niobrara Formation, Denver Basin, Colorado ( USA).

The types of hydrocarbons produced from these chalks are determined by the level of thermal maturity associated with present-day burial or paleoburial conditions. Detailed analyses of deeply-buried chalk from core of the Smoky Hill Chalk Member of the Niobrara Formation in the Champlin Petroleum 2 Boxelder Farms well combined with core data from other Niobrara wells have helped identify many depositional and diagenetic relationships. Porosity of the chalk is proportional to maximum burial depth and inversely proportional to the amount of non-carbonate material (acid- insoluble residue content) in the chalk. Total organic carbon content in the chalk is proportional to the amount of acid-insoluble residue and relative abundance of pyrite in the acid-insoluble fraction. Quartz is inversely proportional to the amount of insoluble material, and the amount of clay tends to increase as insolubles increase, suggesting that detritus in these chalks is greatly influenced by reworked, altered, volcanic products rather than siliceous clastics.-from Authors

Mountain Geologist↗
USGS1988

Stratigraphy, petrology, and provenance of the Albian Blackleaf Formation and the Cenomanian to Turonian lower part of the Frontier Formation in part of Beaverhead and Madison Counties, Montana

The units constitute a dominantly clastic sequence of sandstone, conglomerate, mudstone, and shale deposited in (west) to shallow marine (east) environments. Petrologic and paleocurrent data support an interpretation that Blackleaf and lower Frontier debris was derived from different source areas. -from Authors

Mountain Geologist↗
USGS1988

Facies composition calculated from the sonic, neutron, and density log suite, upper part of the Minnelusa Formation, Powder River basin, Wyoming

Sandstones and dolomites of the Permian upper part of the Minnelusa Formation are treated here as four-component systems consisting of fluid-filled pore space, quartz, dolomite, and anhydrite. Response equations of sonic, neutron, and density logs form a system of four simultaneous equations. With four equations and four unknowns, the composition of upper Minnelusa facies is defined by the three-log suite and can be calculated by solving a 4 ?? 4 matrix. Such calculations of facies composition help in establishing subsurface correlations and yield information on the diagenesis and physical character of upper Minnelusa sandstones and dolomites. Applications of composition calculations are illustrated by examples drawn from the area of the West Mellott field (T52N, R68W), where the upper Minnelusa is at depths of about 7000 ft (2100m). -from Authors

Mountain Geologist↗
USGS1986

Depositional environments of the Rock Springs Formation, southwest flank of the Rock Springs Uplift, Wyoming.

This deltaic Upper Cretaceous Rock Springs Formation of the Mesaverde Group was deposited during early Campanian time near the end of the regressive phase of the Niobrara cyclothem. On the southwest end of the Uplift, part of the delta system is exposed near the seaward edge of a series of transgressive/regressive sequences, which consist of intertonguing prodelta, delta-front, and delta-plain deposits. Eight major delta-front sandstones are vertically stacked and laterally continuous throughout the main study area.-from Author

Mountain Geologist↗
USGS1987

A preliminary report on the bentonite beds of the lower Virgin Creek Member of the Pierre Shale, Stanley County, South Dakota ( USA).

The Virgin Creek Member of the Pierre Shales has been divided by earlier workers into lower and upper zones based on weathering and shale differences. Of the 49 bentonite beds of the lower Virgin Creek, the Government Draw Bentonite Beds, and bentonite bed 20 are the best markers for correlation from stream valley to stream valley. The variation of number and thickness of shale and bentonite beds is due to bioturbation, current activity, differential compaction, basin subsidence, and merging and splitting of bentonite beds. Three distinctive concretion horizons have the potential of also being used as stratigraphic markers within the study area. They include a nodule zone between two bentonite beds, barite(?) concretions that locally mark the lower contact of the Virgin Crrek, and a set of concretions at the contact between the upper and lower Virgin Creek. -from Author

Mountain Geologist↗
USGS1987

Comparing geotechnical to geologic estimates for past overburden in the Pierre-Hayes, South Dakota area: an argument for in-situ pressuremeter determination ( USA).

A knowledge of past overburden thickness is useful for designing underground structures such as waste repositories. This study attempts to determine if a correlation can be made between a geologic estimate and two types of geotechnical calculations of past overburden thickness. In the Pierre-Hayes area, Late Cretaceous Pierre Shales is the only bedrock present, but clasts of the Miocene Ogallala Formation were found in the Pleistocene deposits, suggesting that rocks of the Ogallala Formation once covered this area. Based on the geologic estimate, the Ogallala surface was 1100 ft higher than the present surface. Of the two types of geotechnical data acquired for the Hayes site, the laboratory overconsolidation ratios indicate a past overburden thickness value of 2300 ft, whereas the in situ pressuremeter overconsolidation ratios indicate 1318 ft. We, therefore, believe that in situ determination is a better indicator of past overburden that the laboratory results. However, why the two test results differ to this degree is unknown at present.-from Authors

Mountain Geologist↗
USGS1991

Sedimentology and cyclicity in the Lower Permian De Chelly Sandstone on the Defiance Plateau: Eastern Arizona

The Lower Permian (Leonardian) De Chelly Sandstone crops out along a north-south trend on the Defiance Plateau of eastern Arizona. It is divided into lower and upper members separated by a tongue of the Supai Formation that pinches out to the north. Lithofacies in the De Chelly Sandstone consist of (1) a large-scale trough to tabular- and/or wedge-planar cross-stratified sandstone facies of large-scale eolian dune origin, (2) a small- to medium-scale, trough cross-stratified sandstone also of eolian dune origin, (3) a horizontally stratified, wind-rippled sandstone of sand sheet origin, (4) a wavy, horizontally stratified, wind-rippled sandstone of sabkha origin, and (5) a mud-draped ripple-laminated sandstone of mud-flat origin. The De Chelly Sandstone in the northern Defiance Plateau consists mainly of large-scale dune deposits. Stratigraphic sections in the middle of the plateau are dominated by small- to medium-scale dune and sand sheet deposits whereas those along the southern end of the plateau are composed largely of sabkha and supratidal mud-flat deposits. The lateral distribution of these facies suggests a north-south juxtaposition of central-erg, fore-erg, and mixed sabkha-supratidal depositional environments. Repetitive interbedding of facies in the De Chelly indicates at least twelve depositional cycles in which sabkha and/or supratidal to coastal-plain mud-flats were sequentially overridden by eolian sand sheets and cross-stratified dunes. Lateral and vertical facies relations within the lower and upper members of the De Chelly Sandstone record episodic expansion of the De Chelly erg southward, The comparative abundance of large-scale dune deposits in the upper member suggests that progradation was more extensive during latter stages of deposition. The intervening tongue of Supai Formation and the redbeds that overlie the upper member of the De Chelly at Bonito Canyon document northward transgression of sabkha and supratidal to coastal-plain mud-flat environments. Eolian dune deposition was restricted to the northern Defiance Plateau during deposition of these units.

Arizona↗
USGS1989

Sedimentology and paleontology of the Upper Triassic Chinle Formation, Bedrock, Colorado

Describes a reddish-brown sandstone, siltstone, and mudstone, with minor amounts of siliciclastic-, carbonate-, and chert-pebble conglomerate, and green mudstone. Deposition occurred in continental environments. Lithofacies, trace fossils, and invertebrate and vertebrate fossils indicate that the Late Triassic climate was tropical monsoonal until the close of Chinle deposition when drier seasons became more pronounced. -from Authors

Mountain Geologist↗
USGS1987

Government Draw Bentonite Beds: a newly identified stratigraphic marker in the Virgin Creek Member of the Pierre Shale, central South Dakota ( USA).

A grouping of four bentonite beds, herein named the Government Draw Bentonite Beds, is identified as a stratigraphic marker within the Virgin Creek Member of the Pierre Shale. The beds are found west of Pierre, South Dakota, over an area of at least 130 mi2 (210 km2) where no other markers within the Virgin Creek Member have been identified. In this area, the Government Draw is a potential tool needed to determine the stratigraphic and structural relationships within the upper part of the Pierre Shale, heretofore little known. A better understanding of structural elements found in the Pierre Shale is needed to unravel the Late Cretaceous and younger geologic history of the area. -Authors

Mountain Geologist↗
USGS1986

Southeastern extension of the Lake Basin fault zone in south- central Montana: implications for coal and hydrocarbon exploration ( USA).

The Lake Basin fault zone consists mainly of en echelon NE-striking normal faults that have been interpreted to be surface expressions of left-lateral movement along a basement wrench fault. Information gathered from recent field mapping of coal beds and from shallow, closely-spaced drill holes resulted in detailed coal bed correlations, which revealed another linear zone of en echelon faulting directly on the extended trend of the Lake Basin fault zone. This faulted area, referred to as the Sarpy Creek area, is located 48 km E of Hardin, Montana. It is about 16 km long, 13 km wide, and contains 21 en echelon normal faults that have an average strike of N 63oE. We therefore extend the Lake Basin fault zone 32 km farther SE than previously mapped to include the Sarpy Creek area. The Ash Creek oil field, Wyoming, 97 km due S of the Sarpy Creek area, produces from faulted anticlinal structues that have been interpreted to be genetically related to the primary wrench-fault system known as the Nye-Bowler fault zone. The structural similarities between the Sarpy Creek area and the Ash Creek area indicate that the Sarpy Creek area is a possible site for hydrocarbon accumulation.-from Authors

Mountain Geologist↗
USGS1989

Lower Cretaceous bentonitic strata in southwestern Montana assigned to Vaughn Member of Mowry Shale (East) and of Blackleaf Formation (West)

The Vaughn Member, newly assigned to the Mowry Shale in this report, comprises strata that crop out in the Greenhorn, Gravelly, Madison, and Gallatin ranges, and the Centennial and Beartooth mountains of southwestern Montana. Herein the member is correlated with the Vaughn Member of the Blackleaf Formation, which crops out to the west in the Lima Peaks area, Snowcrest Range, and Pioneer Mountains. Strata assigned to the Vaughn Member of the Blackleaf Formation in southwestern Montana exhibit the same contrasting relationships that exist in northwestern Montana. The Vaughn Member of the Mowry is late Albian in age, determined by bracketing with shallow water marine bivalves in the Muddy Sandstone below and palynomorphs in Mowry strata above. Palynomorphs from the Vaughn Member itself are typically mid-Cretaceous, but do not permit a more exact determination of age. -from Authors

Mountain Geologist↗
USGS1989

Paleogeothermal gradients and timing of oil generation in the Belden Formation, Eagle Basin, northwestern Colorado

Paleogeothermal gradients and timing of oil generation for the Lower and Middle Pennsylvanian Belden Formation have been estimated for four locations in the Eagle Basin of northwestern Colorado, by comparing measured vitrinite reflectance with maturity modeling. Two thermal models were made for each location: one assumes a constant paleogeothermal gradient through time while the other is a two-stage model with changing paleogeothermal gradients. The two-stage paleogeothermal gradient scenario is considered more geologically realistic and is used to estimate the timing of oil generation throughout the Eagle basin. From the data and interpretations, one would expect Belden oil to be found in either upper Paleozoic or Mesozoic reservoir rocks. -Authors

Mountain Geologist↗
USGS1992

Paired, facing monoclines in the Sanpete-Sevier Valley area, central Utah

Several major monoclines that trend northward through the Sanpete-Sevier Valley area of central Utah are paired and face one another. This pairing of monoclines may have occurred when near-horizontal sedimentary and volcanic strata subsided into voids created as salt was removed from a salt diapir concealed beneath valley fill. Removal was mostly by dissolution or extrusion during Neogene time. The paired monoclines, thus, are viewed as collapse features rather than as normal synclinal folds. -from Author

Mountain Geologist↗