Geology topics
Research about Nevada
Source-linked reports with geographic coverage including Nevada.
Hydrogeologic framework of Antelope Valley and Bedell Flat, Washoe County, west-central Nevada
Description of the hydrogeologic framework of Antelope Valley and Bedell Flat in west-central Nevada adds to the general knowledge of regional ground-water flow north of the Reno-Sparks metropolitan area. The hydrogeologic framework is defined by the rocks and deposits that transmit ground water or impede its movement and by the combined thickness of Cenozoic deposits. When data are lacking about the subsurface geology of an area, geophysical methods can be used to provide additional information. In this study, gravimetric and seismic-refraction methods were used to infer the form of structural features and to estimate the thickness of Cenozoic deposits in each of the two valleys. In Antelope Valley, the thickness of these deposits probably does not exceed about 300 feet, suggesting that ground-water storage in the basin-fill aquifer is limited. Beneath Bedell Flat is an elongated, northeast-trending structural depression in the pre-Cenozoic basement; the maximum thickness of Cenozoic deposits is about 2,500 feet beneath the south-central part of the valley. Shallow ground water in the northwest corner of Bedell Flat may be a result of decreasing depth to the pre-Cenozoic basement.
Estimates of evapotranspiration from the Ruby Lake National Wildlife Refuge area, Ruby Valley, northeastern Nevada, May 1999–October 2000
The Ruby Lake National Wildlife Refuge in Ruby Valley, Nevada, contains the largest area of perennial wetlands in northeastern Nevada and provides habitat to a large number of migratory and nesting waterfowl. The long-term preservation of the refuge depends on the availability of sufficient water to maintain optimal habitat conditions. In the Ruby Valley water budget, evapotranspiration (ET) from the refuge is one of the largest components of natural outflow. To help determine the amount of inflow needed to maintain wetland habitat, estimates of ET for May 1999 through October 2000 were made at major habitats throughout the refuge. The Bowen-ratio method was used to estimate daily ET at four sites: over open water, in a moderate-to-dense cover of bulrush marsh, in a moderate cover of mixed phreatophytic shrubs, and in a desert-shrub upland. The eddy-correlation method was used to estimate daily ET for periods of 2 to 12 weeks at a meadow site and at four sites in a sparse-to-moderate cover of phreatophytic shrubs. Daily ET rates ranged from less than 0.010 inch per day at all of the sites to a maximum of 0.464 inch per day at the open-water site. Average daily ET rates estimated for open water and a bulrush marsh were about four to five times greater than in areas of mixed phreatophytic shrubs, where the depth to ground water is less than 5 feet. Based on the seasonal distribution of major habitats in the refuge and on winter and summer ET rates, an estimated total of about 89,000 acre-feet of water was consumed by ET during October 1999-September 2000 (2000 water year). Of this total, about 49,800 acre-feet was consumed by ET in areas of open water and bulrush marsh.
Significance of type Devils Gate Limestone on Devonian proto-Antler forebulge, west of Eureka, Nevada
No abstract available.
Construction and destruction of crinoidal mudmounds on Mississippian Antler forebulge, east of Eureka, Nevada
No abstract available.
Ore-fluid evolution at the Getchell Carlin-type gold deposit, Nevada, USA
Minerals and fluid-inclusion populations were examined using petrography, microthermometry, quadrupole mass-spectrometer gas analyses and stable-isotope studies to characterize fluids responsible for gold mineralization at the Getchell Carlin-type gold deposit. The gold-ore assemblage at Getchell is superimposed on quartz-pyrite vein mineralization associated with a Late-Cretaceous granodiorite stock that intruded Lower-Paleozoic sedimentary rocks. The ore assemblage, of mid-Tertiary age, consists of disseminated arsenian pyrite that contains submicrometer gold, jasperoid quartz, and later fluorite and orpiment that fill fractures and vugs. Late ore-stage realgar and calcite enclose ore-stage minerals. Pre-ore quartz trapped fluids with a wide range of salinities (1 to 21 wt.% NaCl equivalent), gas compositions (H 2 O, CO 2 , and CH 4 ), and temperatures (120 to > 360°C). Oxygen- and hydrogen-isotope ratios indicate that pre-ore fluids likely had a magmatic source, and were associated with intrusion of the granodiorite stock and related dikes. Ore-stage jasperoid contains moderate salinity, aqueous fluid inclusions trapped at 180 to 220°C. Ore fluids contain minor CO 2 and trace H 2 S that allowed the fluid to react with limestone host rocks and transport gold, respectively. Aqueous inclusions in fluorite indicate that fluid temperatures declined to ∼ 175°C by the end of ore-stage mineralization. As the hydrothermal system collapsed, fluid temperatures declined to 155 to 115°C and realgar and calcite precipitated. Inclusion fluids in ore-stage minerals have high δD H2O and δ 18 O H2O values that indicate that the fluid had a deep source, and had a metamorphic or magmatic origin, or both. Late ore-stage fluids extend to lower δ H2O values, and have a wider range of δ 18 O H2O values suggesting dilution by variably exchanged meteoric waters. Results show that deeply sourced ore fluids rose along the Getchell fault system, where they dissolved carbonate wall rocks and deposited gold-enriched pyrite and jasperoid quartz. Gold and pyrite precipitated together as H 2 S in the ore fluids reacted with iron in the host rocks. As ore fluids mixed with local aquifer fluids, ore fluids became cooler and more dilute. Cooling caused precipitation of ore-stage fluorite and orpiment, and late ore-stage realgar. Phase separation and/or neutralization of the ore fluid during the waning stages of the hydrothermal ore system led to deposition of late ore-stage calcite.
Superposed fold-thrust events at the Nevada Test Site
The Nevada Test Site (NTS), in southern Nye County, Nevada, straddles significant pre-Tertiary structural and stratigraphic boundaries. Detailed stratigraphy and biostratigraphy of the Upper Paleozoic section delineates the regional trust sheets and constrains their burial histories. The Paleozoic rocks record three phases of contractional deformation, overprinted by strike-slip faulting. These occurred in the folloing order: (1) foreland-vergant folding and imbricate thrusting in the footwall of the Belted Range thrust; (2) hinterland-vergent folding and thrusting; and (3) north-vergant folding that we interpret as footwall deformation below a third major thrust system. Sinistral slip, typically accompanied by minor east-west shortening, has occurred along a series of north-northeast--north-northwest--striking faults around Yucca Flat. This strike-slip faulting postdates both foreland-vergent and hinterland-vergent deformation, and predates the Cretaceous Climax stock; its age relative to the north-vergent folding and thrusting is unknown. Our new understanding of the geometry of these structures provides new insights into the correlation and interpretation of regional structural features. Field trip stops will examine: (1) the stratigraphic differences that allow us to distinguish the regional thrust sheets and constrain their burial histories; and (2) the field relationships that document the kinematics and relative ages of the penetrative deformational events.
Hydrologic and geologic characteristics of the Yucca Mountain site relevant to the performance of a potential repository
Yucca Mountain, located ~100 mi northwest of Las Vegas, Nevada, has been designated by Congress as a site to be characterized for a potential mined geologic repository for high-level radioactive waste. This field trip will examine the regional geologic and hydrologic setting for Yucca Mountain, as well as specific results of the site characterization program. The first day focuses on the regional setting with emphasis on current and paleo hydrology, which are both of critical concern for predicting future performance of a potential repository. Morning stops will be southern Nevada and afternoon stops will be in Death Valley. The second day will be spent at Yucca Mountain. The field trip will visit the underground testing sites in the "Exploratory Studies Facility" and the "Busted Butte Unsaturated Zone Transport Field Test" plus several surface-based testing sites. Much of the work at the site has concentrated on studies of the unsaturated zone, an element of the hydrologic system that historically has received little attention. Discussions during the second day will compromise selected topics of Yucca Mountain geology, hydrology and geochemistry and will include the probabilistic volcanic hazard analysis and the seismicity and seismic hazard in the Yucca Mountain area. Evening discussions will address modeling of regional groundwater flow, the results of recent hydrologic studies by the Nye County Nuclear Waste Program Office, and the relationship of the geology and hydrology of Yucca Mountain to the performance of a potential repository. Day 3 will examine the geologic framework and hydrology of the Pahute Mesa-Oasis Valley Groundwater Basin and then will continue to Reno via Hawthorne, Nevada and the Walker Lake area.
Reproductive longevity and fecundity associated with nonannual spawning in cui-ui
The cui-ui Chasmistes cujus, a long-lived (40 years or more) and highly fecund catostomid, is often prevented from spawning in drought years. We studied the effect of cui-ui age on egg viability and the effect of nonannual spawning on fecundity in relation to length, age, and growth rate. Egg hatching and survival of swim-up larvae were examined for the offspring of first-time spawners, intermediate-aged females, and old females. Fecundity was tested for three growth categories (fast, intermediate, and slow) in years that were sufficiently wet to allow fish to spawn in the Truckee River and after dry years when fish did not spawn because of river inaccessibility. Females in the fast-growth category were first-time spawners, those in the middle-growth category were young to middle aged, and those in the slow-growth category were middle aged to old. Females up to 44 years of age still had viable eggs and a reproductive life of at least 29 years. Fecundity was greater after no-spawn years (dry year) compared with a spawn year (wet year), especially for fish in the slow-growth category. This study provides insight into the reproductive adaptation of a long-lived western North American catostomid and suggests possible reasons for the wide variation in fecundity in other long-lived catostomids. Our data will be used to improve the accuracy of an existing cui-ui population viability model. The revised model will have greater sensitivity to cui-ui survival relative to their spawning frequency and, thus, contribute to better management of conditions needed for the long-term survival of endangered cui-ui.
Three-dimensional oxygen isotope imaging of convective fluid flow around the Big Bonanza, Comstock lode mining district, Nevada
Oxygen isotope analyses of propylitized andesites from the Con Virginia and California mines allow construction of a detailed, three-dimensional image of the isotopic surfaces produced by the convective fluid flows that deposited the famous Big Bonanza orebody. On a set of intersecting maps and sections, the δ 18 O isopleths clearly show the intricate and conformable relationship of the orebody to a deep, ~500 m gyre of meteoric-hydrothermal fluid that circulated along and above the Comstock fault, near the contact of the Davidson Granodiorite. The core of this gyre (δ 18 O = 0 to 3.8‰) encompasses the bonanza and is almost totally surrounded by rocks having much lower δ 18 O values (–1.0 to –4.4‰). This deep gyre may represent a convective longitudinal roll superimposed on a large unicellular meteoric-hydrothermal system, producing a complex flow field with both radial and longitudinal components that is consistent with experimentally observed patterns of fluid convection in permeable media.
Distribution of the spotted bat (Euderma maculatum) in Nevada, including notes on reproduction
No abstract available.
Geologic and geophysical characterization studies of Yucca Mountain, Nevada, a potential high-level radioactive-waste repository
In recognition of a critical national need for permanent radioactive-waste storage, Yucca Mountain in southwestern Nevada has been investigated by Federal agencies since the 1970's, as a potential geologic disposal site. In 1987, Congress selected Yucca Mountain for an expanded and more detailed site characterization effort. As an integral part of this program, the U.S. Geological Survey began a series of detailed geologic, geophysical, and related investigations designed to characterize the tectonic setting, fault behavior, and seismicity of the Yucca Mountain area. This document presents the results of 13 studies of the tectonic environment of Yucca Mountain, in support of a broad goal to assess the effects of future seismic and fault activity in the area on design, long-term performance, and safe operation of the potential surface and subsurface repository facilities.
Isostatic gravity map of the Battle Mountain 30 x 60 minute quadrangle, north central Nevada
Gravity investigations of the Battle Mountain 30 x 60 minute quadrangle were begun as part of an interagency effort by the U.S. Geological Survey (USGS) and the Bureau of Land Management to help characterize the geology, mineral resources, hydrology, and ecology of the Humboldt River Basin in north-central Nevada. The Battle Mountain quadrangle is located between 40°30' and 41°N. lat. and 116° and 117°W. long. This isostatic gravity map of the Battle Mountain quadrangle was prepared from data from about 1,180 gravity stations. Most of these data are publicly available on a CD-ROM of gravity data of Nevada (Ponce, 1997) and in a published report (Jewel and others, 1997). Data from about 780 gravity stations were collected by the U.S. Geological Survey since 1996; data from about 245 of these are unpublished (USGS, unpub. data, 1998). Data collected from the 400 gravity stations prior to 1996 are a subset of a gravity data compilation of the Winnemucca 1:250,000-scale quadrangle described in great detail by Wagini (1985) and Sikora (1991). This detailed information includes gravity meters used, dates of collection, sources, descriptions of base stations, plots of data, and a list of principal facts. A digital version of the entire data set for the Battle Mountain quadrangle is available on the World Wide Web at: http://wrgis.wr.usgs.gov/docs/gump/gump.html
Preliminary model of the pre-Tertiary basement rocks beneath Yucca Flat, Nevada Test Site, Nevada, based on analysis of gravity and magnetic data
The Environmental Restoration Program of the U.S. Department of Energy, Nevada Operations Office, was developed to investigate the possible consequences to the environment of 40 years of nuclear testing on the Nevada Test Site. The majority of the tests were detonated underground, introducing contaminants into the ground-water system (Laczniak and others, 1996). An understanding of the ground-water flow paths is necessary to evaluate the extent of ground-water contamination. This report provides information specific to Yucca Flat on the Nevada Test Site. Critical to understanding the ground-water flow beneath Yucca Flat is an understanding of the subsurface geology, particularly the structure and distribution of the pre-Tertiary rocks, which comprise both the major regional aquifer and aquitard sequences (Winograd and Thordarson, 1975; Laczniak and others, 1996). Because the pre-Tertiary rocks are not exposed at the surface of Yucca Flat their distribution must be determined through well logs and less direct geophysical methods such as potential field studies. In previous studies (Phelps and others, 1999; Phelps and Mckee, 1999) developed a model of the basement surface of the Paleozoic rocks beneath Yucca Flat and a series of normal faults that create topographic relief on the basement surface. In this study the basement rocks and structure of Yucca Flat are examined in more detail using the basement gravity anomaly derived from the isostatic gravity inversion model of Phelps and others (1999) and high-resolution magnetic data, as part of an effort to gain a better understanding of the Paleozoic rocks beneath Yucca Flat in support of groundwater modeling.
Geologic surface effects of underground nuclear testing, Yucca Flat, Nevada Test Site, Nevada
No abstract available.