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At least 487 records · Page 27Linked to original sources
USGS1979

Preliminary report on the Pierre Shale in North Park, Colorado, and its correlation to Boulder, Middle Park, and Northwest Colorado

The Pierre Shale consists of interbedded marine shale and sandstone representing nearly continuous marine sedimentation during Late Cretaceous time. The Pierre Shale and time-equivalent marine units in the western interior United States contain 28 ammonite range zones. The ammonites show such rapid evolution and such wide geographic extent that their range zones are useful for time-stratigraphic correlation of marine rocks. The Pierre Shale is exposed around the margins of the North Park basin in Colorado where its maximum thickness is about 5,500 feet. The formation overlies the Upper Cretaceous Niobrara Formation and is unconformably overlain by the Paleocene and Eocene Coalmont Formation. The Pierre Shale, which consists of an upper sandy member and a lower shaly member, is primarily marine in origin; however, the sandy member includes minor amounts of coal. Twelve ammonite range zones can be recognized in North Park, including ammonites as old as the early Campanian Baculites obtusus and as young as the early Maestrichtian Baculites eliasi. Zonal distribution indicates that the contact between members becomes older to the northwest. Comparison of the biostratigraphy of the Pierre Shale in North Park with that of the Pierre Shale near Boulder, Colorado, and in Middle Park, and of time-equivalent units in northwestern Colorado, indicates the following: (1) the Pierre Shale in North Park correlates to the upper Mancos Shale, lies Formation, and the lower Williams Fork Formation in northwestern Colorado; (2) two of the three strandlines, represented by nonmarine deposits in the sandy member, correlate to regionally recognized regressions of the Pierre sea; (3) parts of the North and Middle Park structural basin were eroded 1,900-2,300 feet deeper than the Boulder area during the Laramide orogeny; and (4) northwestern North Park was eroded 2,000 feet deeper than northeastern North Park and the area of the stratigraphic section in Middle Park.

Open-File Report↗
USGS1980

Preliminary report on the mineral resource potential of the Red Rocks Escarpment Instant Study area, Clark County, Nevada

The Red Rocks Escarpment Instant Study area in Clark County, Nevada, is 2 mi (32 km) west of Las Vegas and covers about 31,000 acres (12,500 ha) of the rugged Sandstone Bluffs area in the Spring Mountains (fig. 1). It includes the crest of the range, which is slightly higher than 7,200 ft (2,190 m), the Sandstone Bluffs east of the crest where steep cliffs as high as 2,500 ft (760 m) occur, and part of the gently sloping western range front. The Instant Study area (fig. 2) is within land administered by the U.S. Bureau of Land Management.

Nevada↗
USGS1980

Preliminary report on the mineral resources of the Powderhorn Instant study area, Gunnison and Hinsdale counties, Colorado

The Powderhorn Instant Study Area covers approximately 51,000 acres of land under BLM administration located about 80 km (50 mi) southwest of Gunnison, Colorado. A mineral resource survey, made in 1979 by the U.S. Geological Survey and the U.S. Bureau of Mines, indicates that both the mineral potential and the energy potential for the Powderhorn Instant Study Area are low. This report is based on geologic and geochemical investigations, examination of prospects, and an aeromagnetic survey. Spectrographic analyses were made of approximately 120 stream-sediment and rock samples. No mining districts are located within the study area.

Colorado↗
USGS1980

Preliminary report on the geology of the continental slope adjacent to OCS Lease Sale 55, eastern Gulf of Alaska: Petroleum resource implications

Forty samples of Tertiary and Cretaceous outcrop or suspected outcrop were dredged along the 250-km-long northwest-trending continental slope between long 138°00' W. and 142°30' W. These samples, from water depths of 3,150 m to 200 m, combined with seismic reflection data, identify seven rock units in apparently normal stratigraphic position. From oldest to youngest they are: Unit A: Hard graywacke, argillite, and possible intrusive rocks of inferred Late Cretaceous age that crop out in the eastern part of the slope and probably underlie much of the Fairweather Ground. Unit B: At least 900 m of sandstone, conglomerate, shale, and subordinate basaltic volcanic rocks west of Yakutat Seavalley between 142° W. and 143° W. that is not dated but is probably of late Paleocene to early Eocene age. Unit C: 1,300 m of basaltic flow and pyroclastic rocks with associated clastic marine sedimentary rocks that makes up much of the rugged lower slope throughout the area. This sequence is largely, or entirely, of early Eocene age. Unit D: Up to 2,100 m of early and middle Eocene sandstone, conglomerate, siltstone, and tuffaceous organic-rich shale that partly overlies, and partly intertongues with, the volcanic unit. Unit E: 800 m of early to late Eocene and early Oligocene(?) organic-rich shale, tuffaceous shale, siltstone, and sandstone that partly intertongues with, and partly overlies units C and D. Unit F: 300+ m of siltstone, at least in part of late Oligocene age, that crops out locally along the upper slope where it unconformably overlies Unit E. Unit G: Up to 2,000 m of late Cenozoic (middle Miocene? and younger) clastic sedimentary rocks including abundant glaciomarine deposits that unconformably overlie all the older units. The early Tertiary sequence sampled on the continental slope differs strikingly in lithology and structure from coeval rocks exposed onshore or penetrated in unsuccessful exploratory wells on the adjacent mainland. Units B, D, and E include abundant source rocks that have undergone a thermal history resulting in local generation of hydrocarbons. Sandstones from Units D and E locally have secondary porosities up to 31 percent and permeabilities to 36 md. Seismic reflection data indicate that the sequence with the most favorable source and reservoir potential (Units B, D, E) dips northeastward beneath OCS Lease Sale 55 where it could be a favorable exploratory target if involved in suitable traps. Young anticlinal folds are not present, but other important traps are likely to include drape structures, horsts, and faults within the early Tertiary sequence and pinchouts, fault traps, or combination structural/stratigraphic traps along the northeastern margin of the early Tertiary basin.

Alaska↗
USGS1980

Channel erosion and sediment transport in Pheasant Branch basin near Middleton, Wisconsin; a preliminary report

The purpose of this 5-year study is to (1) evaluate the sediment transport, streamflow characteristics, and stream-channel morphology, (2) relate the above to land-use practices; and (3) evaluate the effect that changes in land-use practices will have on Pheasant Branch basin near Middleton, Wis. This report presents findings of sediment transport, streamflow characteristics, and stream-channel morphology from the first year of the study and documents historical erosion. The study is being conducted by the U.S. Geological Survey in cooperation with the city of Middleton and the Wisconsin Geological and Natural History Survey. Pheasant Branch, a tributary to Lake Mendota, drains 23.1 square miles of glacial drift. Channel erosion is severe within Middleton, requiring extensive use of erosion-control structures. Occasionally, channel dredging near the mouth and into Lake Mendota is required for boating. Comparison of stream-channel surveys of 1971 and 1977 shows the lowest part of the channel lowered 3 to 4 feet at some sites in the urban reach from U.S. Highway 12 downstream to Century Avenue. Downstream from Century Avenue, channel width increased from about 35 to 48 feet and channel cross-section area increased about 86 percent. A survey of Pheasant Branch in 1971 provided data for quantification of stream-channel changes since that time. Six erosion-control structures previously installed appear to have had some benefit in controlling head cutting in the channel. (USGS).

Wiscoonsin↗
USGS1980

A preliminary report of the geohydrology of the Mississippi salt-dome basin

The U.S. Department of Energy is investigating the suitability of salt domes in the Mississippi salt-dome basin as repositories for storing radioactive wastes. The Department of Energy has requested that the U.S. Geological Survey describe the groundwater hydrology of the Mississippi salt-dome basin, giving special attention to direction and rate of movement of water. In this first part of a continuing investigation the data obtained from one year of extensive literature search and data compilation are summarized. The regional groundwater hydrology in the salt-dome basin is defined with respect to (1) groundwater flow, (2) facies changes, (3) geological structure, (4) recharge and discharge, (5) freshwater-saltwater relations, and (6) identification of localities where additional data are needed. From the 50 piercement-type salt domes in the Mississippi salt-dome basin three domes (Richton, Cypress Creek, and Lampton) were selected for more intensive study. To further evaluate the geohydrology of Richton, Lampton, and Cypress Creek domes as possible sites for storage of radioactive waste, an intensive geohydrologic study based on a comprehensive test drilling program near the domes is planned. (USGS)

Mississippi↗