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At least 1,441 records · Page 80Linked to original sources
USGS2004

Bedrock geology and mineral resources of the Knoxville 1° x 2° quadrangle, Tennessee, North Carolina, and South Carolina

The Knoxville 1°x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesvil Ie fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or silli manite grade of Manuscript approved for publication February 22, 1991. regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1°x2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge, Vermiculite produced from a large deposit near Tigerville, S.C-, in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains Abstract Figure 1. Location of the Knoxville 1ºx2º quadrangle, with state and county boundaries National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

North Carolina, South Carolina, Tennessee↗
USGS1961

Geologic control of mineral composition of stream waters of the eastern slope of the Southern Coast Ranges, California

Chemical analyses of waters of streams that drain the semiarid eastern slope of the southern Coast Ranges in California demonstrate that differences in the anion composition, especially in the ratio of bicarbonate to sulfate, are related chiefly to the lithologic character of the rocks exposed in the tributary drainage area. Where more than hall the drainage area of a typical eastern-slope stream is underlain by clastic marine sedimentary rocks of Jurassic and Cretaceous age, bicarbonate generally predominates over sulfate; the ratio of bicarbonate to sullate, both expressed in equivalents per million, in samples of the streams at low-flow stage ranges from 0.8 to 6. Conversely, where more than hall the drainage area is underlain by marine and continental deposits of Tertiary age and continental deposits of Quaternary age, sulfate predominates over bicarbonate, and the ratio of bicarbonate to sulfate in samples taken during the low-flow stage ranges from 0.02 to 0.7. Organic siliceous marine shale of Tertiary age deposited in a reducing environment is probably the primary source of sullate in the region. Secondary deposits of sulfate minerals, chiefly gypsum, which are abundant in the continental deposits of late Tertiary and Quaternary age, also contribute sullate to the stream waters.

Water Supply Paper↗
USGS2005

Subduction erosion of the Jurassic Talkeetna-Bonanza arc and the Mesozoic accretionary tectonics of western North America

The Jurassic Talkeetna volcanic arc of south-central Alaska is an oceanic island arc that formed far from the North American margin. Geochronological, geochemical, and structural data indicate that the arc formed above a north-dipping subduction zone after ca. 201 Ma. Magmatism migrated northward into the region of the Talkeetna Mountains ca. 180 Ma. We interpret this magmatism as the product of removal of the original forearc while the arc was active, mainly by tectonic erosion. Rapid exhumation of the arc after ca. 160 Ma coincided with the sedimentation of the coarse clastic Naknek Formation. This exhumation event is interpreted to reffect collision of the Talkeetna arc with either the active margin of North America or the Wrangellia composite terrane to the north along a second north-dipping subduction zone. The juxtaposition of accreted trench sedimentary rocks (Chugach terrane) against the base of the Talkeetna arc sequence requires a change from a state of tectonic erosion to accretion, probably during the Late Jurassic (before 150 Ma), and definitely before the Early Cretaceous (ca. 125 Ma). The change from erosion to accretion probably reflects increasing sediment flux to the trench due to collision ca. 160 Ma. ?? 2005 Geological Society of America.

Geology↗
USGS2006

High REE and Y concentrations in Co-Cu-Au ores of the Blackbird district, Idaho

Analysis of 11 samples of strata-bound Co-Cu-Au ore from the Blackbird district in Idaho shows previously unknown high concentrations of rare earth elements (REE) and Y, averaging 0.53 wt percent ???REE + Y oxides. Scanning electron microscopy indicates REE and Y residence in monazite, xenotime, and allanite that form complex intergrowths with cobaltite, suggesting coeval Co and REE + Y mineralization during the Mesoproterozoic. Occurrence of high REE and Y concentrations in the Blackbird ores, together with previously documented saline-rich fluid inclusions and Cl-rich biotite, suggest that these are not volcanogenic massive sulfide or sedimentary exhalative deposits but instead are iron oxide-copper-gold (IOCG) deposits. Other strata-bound Co deposits of Proterozoic age in the North American Cordillera and elsewhere in the world may have potential for REE and Y resources. IOCG deposits with abundant light REE should also be evaluated for possible unrecognized heavy REE and Y mineralization. ?? 2006 by Economic Geology.

Economic Geology↗
USGS2003

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

IMAP↗
USGS1957

Geology and ground-water resources of Goshen County Wyoming with a section on chemical quality of the ground water

Goshen County, which has an area of 2,186 square miles, lies in southeastern Wyoming. The purpose of this study was to evaluate the ground-water resources of the county by determining the character, thickness, and extent of the waterbearing materials; the source, occurrence, movement, quantity, and quality of the ground water; and the possibility of developing additional ground water. The rocks exposed in the area are sedimentary and range in age from Precambrian to Recent. A map that shows the areas of outcrop and a generalized section that summarizes the age, thickness, physical character, and water supply of these formations are included in the report. Owing to the great depths at which they lie beneath most of the county, the formations older than the Lance formation of Late Cretaceous age are not discussed in detail. The Lance formation, of Late Cretaceous age, which consists mainly of beds of fine-grained sandstone and shale, has a maximum thickness of about 1,400 feet. It yields water, which usually is under artesian pressure, to a large number of domestic and stock wells in the south-central part of the county. Tertiary rocks in the area include the Chadron and Brule formations of Oligocene age, the Arikaree formation of Miocene age, and channel deposits of Pliocene age. The Chadron formation is made up of two distinct units: a lower unit of highly variegated fluviatile deposits that has been found only in the report area; and an upper unit that is typical of the formation as it occurs in adjacent areas. The lower unit, which ranges in thickness from a knife edge to about 95 feet, is not known to yield water to wells, but its coarse-grained channel deposits probably would yield small quantities of water to wells. The upper unit, which ranges in thickness from a knife edge to about 150 feet, yields sufficient quantities of water for domestic and stock uses from channel deposits of sandstone under artesian pressure. The Brule formation, which is mainly a siltstone, ranges in thickness from a knife edge to about 450 feet and yields water to domestic and stock wells from fractures and from lenses of sandstone. The Arikaree formation ranges in thickness from a knife edge to about 1,000 feet, and yields water to several domestic and stock wells in the northwestern part of the area. The Pliocene channel deposits, which probably do not exceed 25 feet in thickness, are not a source of water for wells in Goshen County. The upland deposits, which are mainly of Pleistocene age, generally are dry and do not serve as aquifers; however, test drilling revealed several deep, buried channels occupied by deposits which probably would yield moderate quantities of water to wells if a sufficient saturated thickness were penetrate The deposits of the third terrace, which are of Pleistocene age, range in thickness from a knife edge to about 210 feet and yield water to a large number of irrigation wells in the area. The flood-plain deposits, which are of Pleistocene and Recent age, range in thickness from a knife edge to about 200 feet. Those in the valley of the North Platte River yield abundant water to many large supply wells. The flood-plain deposits along the valley of Rawhide Creek consist mainly of fine-grained materials and yield large supplies of water to well only in the lower stretches of the creek valley near its confluence with the valley of the North Platte River. The deposits along the valleys of Horse and Bear Creeks generally are relatively thin and fine grained. In the vicinity of Ls grange, however, the deposits, which are about 45 feet thick, yield moderate, supplies of water to several irrigation wells. Other Recent deposits in the area--dune sand, loesslike deposits, and slope wash--generally are fine grained and relatively thin and, hence, are not important sources of ground water. The unconsolidated sand and gravel of the flood-plain and terrace deposits are the principal aquifers in the area.

Wyoming↗
USGS1964

Geology and ground water of the Luke area, Maricopa County, Arizona

Luke Air Force Base, in the Salt River Valley in central Arizona. is within an intermontane basin--the Phoenix basin--in the Basin and Range lowlands province. The Luke area, the subject of this study, extends beyond the limits of the base. Ground-water resources of the Luke area were studied to determine the possibility of developing a water supply of optimum quantity and quality to supplement the base supply. Several wells drilled for this purpose, prior to the study, either produced an inadequate supply of water or produced ware-that had a high dissolved-solids content. The Phoenix basin is filled with unconsolidated to semiconsolidated Tertiary and Quaternary sedimentary rocks that are referred to as valley fill. Although its total thickness is unknown, 2,784 feet of valley fill--primarily consisting of clay, silt, sand, and gravel--has been penetrated. Percentage-distribution maps of fine-grained materials indicate a gross-facies pattern and a selective depositional area of the valley-fill materials. The maps also indicate that the areal distribution of fine-grained materials increases with depth. In general, the better producing wells, regardless of depth, are in areas where tee valley fill is composed of less than 60 percent fine-grained materials. The water table in the area is declining because large quantities of water are withdrawn and recharge is negligible. The decline near Luke Air Force Base during the period 1941-61 was about 150 feet. Ground water was moving generally southwest in the spring of 1961. Locally, changes in the direction of movement indicate diversion toward two major depressions. The dissolved-solids content of the ground water ranged from about 190 to 6,300 ppm. The highest concentration of dissolved solids is in water from the southern part of the area and seems to come from relatively shallow depths; wells in the northern part generally yield water of good quality. After a reconnaissance of the area, the U.S. Geological Survey located and supervised the drilling of two test wells--wells (B-2-1) 9bcb and (B-2-1) 5abc?on Luke Air Force Base. The quantity of water produced by the wells was adequate. The dissolved-solids content of water from the wells was low, and the overall quality of water from well (B-2-1) 5abc was good. When well (B-2-1) 9bcb was perforated between 907 and 977 feet, the water had a fluoride concentration of 4.4 ppm; however, the fluoride concentration decreased to 2.8 ppm when new perforations were cut at a shallower depth, and it was decided that dilution with other base water supplies probably would alleviate any possible fluoride problem.

Water Supply Paper↗
USGS1990

Geochemical evidence for Se mobilization by the weathering of pyritic shale, San Joaquin Valley, California, U.S.A.

Acidic (pH 4) seeps issue from the weathered Upper Cretaceous-Paleocene marine sedimentary shales of the Moreno Formation in the semi-arid Coast Ranges of California. The chemistry of the acidic solutions is believed to be evidence of current reactions ultimately yielding hydrous sodium and magnesium sulfate salts, e.g. mirabilite and bloedite, from the oxidation of primary pyrite. The selenate form of Se is concentrated in these soluble salts, which act as temporary geological sinks. Theoretically, the open lattice structures of these hydrous minerals could incorporate the selenate (SeO 4 −2 ) anion in the sulfate (SO 4 −2 ) space. When coupled with a semi-arid to arid climate, fractional crystallization and evaporative concentration can occur creating a sodium-sulfate fluid that exceeds the U.S. Environmental Protection Agency limit of 1000 μg l −1 for a toxic Se waste. The oxidative alkaline conditions necessary to ensure the concentration of soluble selenate are provided in the accompanying marine sandstones of the Panoche and Lodo Formations and the eugeosynclinal Franciscan assemblage. Runoff and extensive mass wasting in the area reflect these processes and provide the mechanisms which transport Se to the farmlands of the west-central San Joaquin Valley. Subsurface drainage from these soils consequently transports Se to refuge areas in amounts elevated to cause a threat to wildlife.

California↗
USGS2005

Vitrinite reflectance data for the Permian Basin, west Texas and southeast New Mexico

This report presents a compilation of vitrinite reflectance (Ro) data based on analyses of samples of drill cuttings collected from 74 boreholes spread throughout the Permian Basin of west Texas and southeast New Mexico (fig. 1). The resulting data consist of 3 to 24 individual Ro analyses representing progressively deeper stratigraphic units in each of the boreholes (table 1). The samples, Cambrian-Ordovician to Cretaceous in age, were collected at depths ranging from 200 ft to more than 22,100 ft. The R 0 data were plotted on maps that depict three different maturation levels for organic matter in the sedimentary rocks of the Permian Basin (figs. 2-4). These maps show depths at the various borehole locations where the R 0 values were calculated to be 0.6 (fig. 2), 1.3 (fig. 3), and 2.0 (fig. 4) percent, which correspond, generally, to the onset of oil generation, the onset of oil cracking, and the limit of oil preservation, respectively. The four major geologic structural features within the Permian Basin–Midland Basin, Delaware Basin, Central Basin Platform, and Northwest Shelf (fig. 1) differ in overall depth, thermal history and tectonic style. In the western Delaware Basin, for example, higher maturation is observed at relatively shallow depths, resulting from uplift and eastward basin tilting that began in the Mississippian and ultimately exposed older, thermally mature rocks. Maturity was further enhanced in this basin by the emplacement of early and mid-Tertiary intrusives. Volcanic activity also appears to have been a controlling factor for maturation of organic matter in the southern part of the otherwise tectonically stable Northwest Shelf (Barker and Pawlewicz, 1987). Depths to the three different Ro values are greatest in the eastern Delaware Basin and southern Midland Basin. This appears to be a function of tectonic activity related to the Marathon-Ouachita orogeny, during the Late-Middle Pennsylvanian, whose affects were widespread across the Permian Basin. The Central Basin Platform has been a positive feature since the mid to-late Paleozoic, during which time sedimentation occurred along its flanks. This nonsubsidence, along with the lack of supplemental heating (volcanism), implies lower maturation levels.

New Mexico, Texas↗
USGS1962

Bedrock geology of the Mount Carmel and Southington quadrangles, Connecticut

New data concerning the geologic structure, stratigraphy, petrography, origin, and ages of bedrock formations in an area of approximately 111 square miles in south-central Connecticut were obtained in the course of detailed geologic mapping from 1957 to 1960. Mapping was done at a scale of 1:24,000 on topographic base maps having a 10-foot contour interval. Bedrock formations are classified in two principal categories. The first includes metasedimentary, meta-igneous, and igneous rocks of Precambrian to Devonian age, which crop out in the western parts of both quadrangles. The second includes sedimentary and igneous rocks of the Newark Group of Late Triassic age, which crop out in the eastern parts of the quadrangles. Diabase dikes, which are Late Triassic or younger in age, intruded rocks in both the western and eastern parts of the map area. Rocks in the western part of the area underwent progressive regional metamorphism in Middle to Late Devonian time. The arrangement of the chlorite, garnet, biotite, staurolite, and kyanite zones here is approximately the mirror-image of metamorphic zones in Dutchess County, New York. However, garnet appeared before biotite in politic rocks in the map area, because the ration MgO/FeO is low. Waterbury Gneiss and the intrusive Woodtick Gneiss are parts of a basement complex of Precambrian age, which forms the core of the Waterbury dome. This structure is near the southern end of a line of similar domes that lie along the crest of a geanticline east of the Green Mountain anticlinorium. The Waterbury Gneiss is believed to have been metamorphosed in Precambrian time as well as in Paleozoic time. The Woodtick Gneiss also may have been metamorphosed more than once. In Paleozoic time, sediments were deposited in geosynclines during two main cycles of sedimentation. The Straits, Southington Mountain, and Derby Hill Schists, which range in age from Cambrian to Ordovician, reflect a transition from relatively clean politic sediments to thinly layered sediments that contained rather high percentages of fine-grained volcanic debris. Metadiabase and metabasalt extrusives above Derby Hill Schist south of the map area represent more intense volcanic activity before or during the early stages of the Taconic disturbance in Late Ordovician time. Impure argillaceous, siliceous, and minor calcareous sediments of the Wepawaug Schist, which is Silurian and Devonian in age, were deposited unconformably on older rocks during renewed subsidence of a geosyncline. The Wepawaug now occupies the trough of a tight syncline, which formed before and during progressive regional metamorphism at the time of the Acadian orogeny in middle to Late Devonian time. Felsic igneous rocks were intruded into the metasedimentary formations of Paleozoic age before the climax of the latest progressive regional metamorphism. Intrusives that gave rise to the Prospect and Ansonia Gneisses were emplaced mainly in the Southington Mountain Schist, and the igneous rocks as well as the host rocks were metamorphosed in the staurolite zone. Although it is possible that these two intrusives were emplaced during the Taconic disturbance, the writer believes it more likely that the igneous rocks from which the Prospect and Ansonia Gneisses formed were emplaced during the Acadian orogeny. Woodbridge Granite, which intruded the Wepawaug Schist, is Devonian in age and undoubtedly was emplaced during the Acadian orogeny. In this area the granite is essentially unmetamorphosed, because it is in the chlorite, garnet, and biotite zones. Southwest of the map area, however, metamorphic equivalents of the Woodbridge are found in Wepawaug Schist in the staurolite zone. The Ansonia Gneiss, therefore, may be a metamorphic equivalent of the Woodbridge Granite. Rocks of Late Triassic age formerly covered the entire map area, but were eroded from the western part after tilting and faulting in Late Triassic time. The New Haven Arkose of the Newark

Open-File Report↗
USGS1982

Hydrology of the low-level radioactive solid waste burial site and vicinity near Barnwell, South Carolina

Geologic and hydrologic conditions at a burial site for low-level radioactive waste were studied, and migration of leachates from the buried waste into surrounding unconsolidated sediments were evaluated. The burial site and vicinity are underlain by a sequence of unconsolidated sediments of Late Cretaceous, Tertiary, and Quaternary age. These sediments are deposited over a graben which has been filled with sedimentary rocks of Triassic age. Hydraulic properties of the sediments beneath the burial site were determined by laboratory and field tests. Laboratory hydraulic conductivity values ranged from about 10^-7 to 10^-1 feet per day for the clayey sediments to nearly 22 feet per day for aquifer sands. Field aquifer tests indicate a transmissivity of about 22,000 feet squared per day for Cretaceous sediments and about 6,000 feet squared per day for Tertiary sediments. Aquifer tests indicate heterogeneity in the upper 200 feet of the Tertiary sediments. Water samples were analyzed from 51 wells, 5 streams, a Carolina bay, and rainfall at the burial site. The total dissolved solids of the ground water ranged from about 7 to 40 milligrams per liter in the upper clayey sediments to about 150 milligrams per liter in the water in the deeper calcareous sediments. The pH of the ground water ranges from 4.8 to 6.5. This slightly acidic water is corrosive to buried metal. Tritium activity greater than background was detected in sediment cores taken from drill holes adjacent to the burial trenches. High tritium activity occurred at depths above the trench floor. This indicates upward movement of water or vapor to the land surface. Tritium and organic constituents greater than background concentrations were observed in a monitoring well about 10 feet from a trench, indicating lateral migration of radionuclides from the buried waste. Traces of cobalt-60 and tritium greater than background activity were observed in sediment cores collected 5.8 feet beneath the trench floor at one site. A hydrologic model was used to simulate ground-water flow in the study area. Based on the model results the minimum time of travel for ground water to move from the burial site to the nearest stream, Marys Branch Creek, is about 50 years. Radionuclides will move more slowly than the water, and will diminish in activity, because of dispersion and radioactive decay.

South Carolina↗
USGS1979

Geology and tectonic development of the continental margin north of Alaska

The continental margin north of Alaska, as interpreted from seismic reflection profiles, is of the Atlantic type and consists of three sectors of contrasting structure and stratigraphy. The Chukchi sector, on the west, is characterized by the deep late Mesozoic and Tertiary North Chukchi basin and the Chukchi Continental Borderland. The Barrow sector of central northern Alaska is characterized by the Barrow arch and a moderately thick continental terrace build of Albian to Tertiary clastic sediment. The terrace sedimentary prism is underlain by lower Paleozoic metasedimentary rocks. The Barter Island sector of northeastern Alaska and Yukon Territory is inferred to contain a very thick prism of Jurassic, Cretaceous and Tertiary marine and nonmarine clastic sediment. Its structure is dominated by a local deep Tertiary depocenter and two regional structural arches. We postulate that the distinguishing characteristics of the three sectors are inherited from the configuration of the rift that separated arctic Alaska from the Canadian Arctic Archipelago relative to old pre-rift highlands, which were clastic sediment sources. Where the rift lay relatively close to northern Alaska, in the Chukchi and Barter Island sectors, and locally separated Alaska from the old source terranes, thick late Mesozoic and Tertiary sedimentary prisms extend farther south beneath the continental shelf than in the intervening Barrow sector. The boundary between the Chukchi and Barrow sectors is relatively well defined by geophysical data, but the boundary between the Barrow and Barter Island sectors can only be inferred from the distribution and thickness of Jurassic and Cretaceous sedimentary rocks. These boundaries may be extensions of oceanic fracture zones related to the rifting that is postulated to have opened the Canada Basin, probably beginning during the Early Jurassic.

Alaska↗
USGS2012

Gulf of Mexico Gas Hydrate Joint Industry Project Leg II logging-while-drilling data acquisition and analysis

One of the objectives of the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (GOM JIP Leg II) was the collection of a comprehensive suite of logging-while-drilling (LWD) data within gas-hydrate-bearing sand reservoirs in order to make accurate estimates of the concentration of gas hydrates under various geologic conditions and to understand the geologic controls on the occurrence of gas hydrate at each of the sites drilled during this expedition. The LWD sensors just above the drill bit provided important information on the nature of the sediments and the occurrence of gas hydrate. There has been significant advancements in the use of downhole well-logging tools to acquire detailed information on the occurrence of gas hydrate in nature: From using electrical resistivity and acoustic logs to identify gas hydrate occurrences in wells to where wireline and advanced logging-while-drilling tools are routinely used to examine the petrophysical nature of gas hydrate reservoirs and the distribution and concentration of gas hydrates within various complex reservoir systems. Recent integrated sediment coring and well-log studies have confirmed that electrical resistivity and acoustic velocity data can yield accurate gas hydrate saturations in sediment grain supported (isotropic) systems such as sand reservoirs, but more advanced log analysis models are required to characterize gas hydrate in fractured (anisotropic) reservoir systems. In support of the GOM JIP Leg II effort, well-log data montages have been compiled and presented in this report which includes downhole logs obtained from all seven wells drilled during this expedition with a focus on identifying and characterizing the potential gas-hydrate-bearing sedimentary section in each of the wells. Also presented and reviewed in this report are the gas-hydrate saturation and sediment porosity logs for each of the wells as calculated from available downhole well logs.

Gulf Of Mexico↗
USGS2007

Metallogeny of the nikolai large igneous province (LIP) in southern alaska and its influence on the mineral potential of the talkeetna mountains

Recent geologic mapping has identified areas of extrusive basalts of the Middle to Late Triassic Nikolai Greenstone within the Wrangellia terrane that extend at least 80 km southwest of their previously known extent. Abundant dolerite sills of similar composition intrude Paleozoic and Mesozoic stratigraphy below the Nikolai throughout the central Talkeetna Mountains. The Talkeetna Mountains, therefore, have newly identified potential for copper, nickel, and platinum-group elements (PGEs) as disseminated, net-textured, or massive magmatic sulfide deposits hosted in mafic and ultramafic sill-form complexes related to emplacement of the Nikolai. Because of their potential high grades, similar magmatic sulfide targets have been the focus of increasing mineral exploration activity over the last decade in the Amphitheater Mountains and central Alaska Range, 100-200 km to the northeast. The Nikolai Greenstone, associated intrusions, and their metamorphosed equivalents also have potential to host stratabound disseminated "basaltic copper" deposits. Sedimentary and metasedimentary rocks overlying the Nikolai have the potential to host stratabound, disseminated, or massive "reduced-facies" type Cu-Ag deposits. Ultramafic rocks have been identified only in the extreme northeastern Talkeetna Mountains to date. However, coincident gravity and magnetic highs along the leading (northwestern) edge of and within Wrangellia in the Talkeetna and Clearwater Mountains suggest several areas that are highly prospective for ultramafic rocks related to extrusion of Nikolai lavas. In particular, the distribution, geometry, and composition of sills within the pre-Nikolai stratigraphy and the structural and tectonic controls on intrusive versus extrusive rock distribution deserve serious examination. Copyright ?? 2007 The Geological Society of America.

Special Paper of the Geological Society of America↗
USGS2004

Geochronology of the western and central Brooks Range, Alaska: Implications for the geologic evolution of the Anarraaq and Red Dog Zn-Pb-Ag deposits

A compilation of published geochronology of rocks and minerals from the western and central Brooks Range provides a framework for understanding the complex history of the Brooks Range and northern Alaska. A simplified timeline of events comprises (1) Devonian extension, (2) Mississippian extension and Zn-Pb-Ag mineralization, (3) a passive interval, (4) pre-Brooks Range orogeny rock-formation and thermal event, (5) inception of Brooks Range orogeny, (6) exhumation and the end of main-stage deformation, and (7) subsequent episodic deformation. This compilation is supplemented by new 40Ar/39Ar dates of white mica from the Anarraaq and Red Dog Zn-Pb-Ag (+ barite) deposits from the western Brooks Range. The deposits are hosted in black shale and carbonate rocks of the Late Mississippian-Early Pennsylvanian Kuna Formation. Quartz-pyrite-white mica grains in sedimentary rocks above the Anarraaq deposit yield an age of 195.0 ?? 2.0 Ma, and paragenetically late quartz-pyrite-white mica from the Main orebody at the Red Dog deposit has an age of 126.1 ?? 0.7 Ma. These white micas are much younger than the age of Zn-Pb-Ag mineralization at Red Dog (338 ?? 5.8 Ma Re-Os age of pyrite). The date for white mica from Anarraaq (???195 Ma) appears to be related to a large-scale thermal event in the region immediately before the inception of the Brooks Range orogeny. The white mica from the Red Dog deposit (???126 Ma) correlates with the later stages of the orogeny, a period of blueschist metamorphism, extension, and rapid exhumation, which varied with geographic location. These dates suggest that the Red Dog deposits underwent significant hydrothermal overprinting during multiple episodes of the Brooks Range orogeny. ?? 2004 by Economic Geology.

Economic Geology↗
USGS2006

Sedimentary textures formed by aqueous processes, Erebus crater Meridiani Planum, Mars

New observations at Erebus crater (Olympia outcrop) by the Mars Exploration Rover Opportunity between sols 671 and 735 (a sol is a martian day) indicate that a diverse suite of primary and penecontemporaneous sedimentary structures is preserved in sulfate-rich bedrock. Centimeter-scale trough (festoon) cross-lamination is abundant, and is better expressed and thicker than previously described examples. Postdepositional shrinkage cracks in the same outcrop are interpreted to have formed in response to desiccation. Considered collectively, this suite of sedimentary structures provides strong support for the involvement of liquid water during accumulation of sedimentary rocks at Meridiani Planum.

Geology↗
USGS2004

Gravity study through the Tualatin Mountains, Oregon: Understanding crustal structure and earthquake hazards in the Portland urban area

A high-resolution gravity survey through the Tualatin Mountains (Portland Nills) west of downtown Portland exhibits evidence of faults previously identified from surface geologic and aeromagnetic mapping. The gravity survey was conducted in 1996 along the 4.5-km length of a twin-bore tunnel, then under construction and now providing light-rail service between downtown Portland and communities west of the Portland Hills. Gravitational attraction gradually increases from west to east inside the tunnel, which reflects the tunnel's location between low-density sedimentary deposits of the Tualatin basin to the west and high-density, mostly concealed Eocene basalt to the east. Superimposed on this gradient are several steplike anomalies that we interpret as evidence for faulted contacts between rocks of contrasting density. The largest of these anomalies occurs beneath Sylvan Creek, where a fault had previously been mapped inside the tunnel. Another occurs 1200 m from the west portal, at the approximate intersection of the tunnel with an aeromagnetic anomaly associated with the Sylvan fault (formerly called the Oatfield fault). Lithologic cross sections based on these gravity data show that the steplike anomalies are consistent with steeply dipping reverse faults, although strike-slip displacements also may be important. Three gravity lows correspond with topographic lows directly overhead and may reflect zones of shearing. Several moderate earthquakes (M ??? 3.5) occurred near the present-day location of the tunnel in 1991, suggesting that some of these faults or other faults in the Portland Hills fault zone are seismically active.

Bulletin of the Seismological Society of America↗
USGS2012

Integration of new geologic mapping and satellite-derived quartz mapping yields insights into the structure of the Roberts Mountains allochthon applicable to assessments for concealed Carlin-type gold deposits

Geologic mapping and remote sensing across north-central Nevada enable recognition of a thick sheet of Middle and Upper Ordovician Valmy Formation quartzite that structurally overlies folded and faulted Ordovician through Devonian stratigraphic units of the Roberts Mountains allochthon. In the northern Independence Mountains and nearby Double Mountain area, the Valmy Formation is in fault contact with Ordovician through Silurian, predominantly clastic, sedimentary rocks of the Roberts Mountains allochthon that were deformed prior to, or during, emplacement of the Valmy thrust sheet. Similar structural relations are recognized discontinuously for 200 kilometers along the strike of the Roberts Mountains allochthon in mapping guided by regional remote-sensing-based (ASTER) quartz maps. Overall thicknesses of deformed Roberts Mountains allochthon units between the base of the Valmy and the top of underlying carbonate rocks that host large Carlin-type gold deposits varies on the order of hundreds of meters but is not known to exceed 700 meters. The base of the Valmy thrust sheet is a complimentary datum in natural resource exploration and mineral resource assessment for concealed Carlin-type gold deposits.

Nevada↗