USGS Science⌕ Search

SEARCH · USGS Science

Results for “World & I”

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 1,495 records · Page 83Linked to original sources
USGS1981

Significant results from using earth observation satellites for mineral and energy resource exploration

A large number of Earth-observation satellites orbit our world several times each day, providing new information about the land and sea surfaces and the overlying thin layer of atmosphere that makes our planet unique. Meteorological satellites have had the longest history of experimental use and most are now considered operational. The geologic information collected by the Landsat, Polar Orbiting Geophysical Observatory (POGO), Magsat, Heat Capacity Mapping Mission (HCMM) and Seasat land and ocean observation systems is being thoroughly tested, and some of these systems are now approaching operational use. Landsat multispectral images provide views of large areas of the Earth under uniform lighting conditions and can be obtained at a variety of scales and formats. Not only do the Landsat data provide highly useful images showing surficial materials and structures such as folds and faults, but also measurements and computer-derived ratios of the brightness of different rock types, alteration zones, and mineral associations. These data have led to the finding of a variety of new ore deposits. In addition, the combination of Landsat digital data and aeromagnetic data has extended the use of Landsat as an exploration tool which can be used to readily relate surface features to subsurface anomalies. Magsat data, now being collected, are helping refine information on major crustal anomalies that were first recognized during the analysis of POGO data. The more nearly circular orbit, lower altitude, and increased sophistication of its vector magnetometer enable Magsat to provide more precise information than POGO. Information of this type is required to develop crustal models. Although Magsat is designed to operate for only 4–8 months, the number of orbits that it should be able to make will be sufficient to accomplish its mission and to record a major magnetic storm expected in 1980. HCMM is a two-band visible to near-IR (0.55–1.1 μm) and thermal infrared (10.2–12.5 μm) system designed to measure reflected solar energy, determine the heat capacity of rocks and to monitor soil moisture, thermal effluents, plant canopy temperatures and snow cover. Launched in April 1978, it is in sun-synchronous, circular orbit at an altitude of 620 km. It is a relatively low-resolution system with an instantaneous field of view (IFOV) of 500–600 m and a swath width of 716 km. However, the system is designed to detect objects in the range of 260°–340° K with a sensitivity (NEδT) of 0.4°K at 280°. Recording the thermal radiation of urban heat islands and high thermal inertia of quartzite strata in the Appalachian region are two examples of its land applications. Launched in June 1978, Seasat operated for only 100 days, but successfully acquired much information over both sea and land. The collection of synthetic aperture radar (SAR) imagery and radar altimetry was particularly important to geologists. Although there are difficulties in processing and distributing these data in a timely manner, initial evaluations indicate that the radar imagery supplements Landsat data by increasing the spectral range and offering a different look angle. The radar altimeter provides accurate profiles over narrow strips of land (1 km wide) and has demonstrated usefulness in measuring icecap surfaces (Greenland, Iceland, and Antarctica). The Salar of Uyuni in southern Bolivia served as a calibration site for the altimeter and has enabled investigators to develop a land-based smoothing algorithm that is believed to increase the accuracy of the system to 10 cm. Data from the altimeter are currently being used to measure subsidence resulting from ground water withdrawal in the Phoenix-Tucson area.

Advances in Space Research↗
USGS1974

Bimodal tholeiitic-dacitic magmatism and the Early Precambrian crust

Interlayered plagioclase-quartz gneisses and amphibolites from 2.7 to more than 3.6 b.y. old form much of the basement underlying Precambrian greenstone belts of the world; they are especially well-developed and preserved in the Transvaal and Rhodesian cratons. We postulate that these basement rocks are largely a metamorphosed, volcanic, bimodal suite of tholeiite and high-silica low-potash dacite—compositionally similar to the 1.8-b.y.-old Twilight Gneiss — and partly intrusive equivalents injected into the lower parts of such volcanic piles. We speculate that magmatism in the Early Precambrian involved higher heat flow and more hydrous conditions than in the Phanerozoic. Specifically, we suggest that the early degassing of the Earth produced a basaltic crust and pyrolitic upper mantle that contained much amphibole, serpentine, and other hydrous minerals. Dehydration of the lower parts of a downgoing slab of such hydrous crust and upper mantle would release sufficient water to prohibit formation of andesitic liquid in the upper part of the slab. Instead, a dacitic liquid and a residuum of amphibole and other silica-poor phases would form, according to Green and Ringwood's experimental results. Higher temperatures farther down the slab would cause total melting of basalt and generation of the tholeiitic member of the suite. This type of magma generation and volcanism persisted until the early hydrous lithosphere was consumed. An implication of this hypothesis is that about half the present volume of the oceans formed before about 2.6 b.y. ago.

Precambrian Research↗
USGS1985

Crystalline gold in soil and the problem of supergene nugget formation: Freezing and exclusion as genetic mechanisms

Many of the world's richest gold placer deposits now occur in cold regions despite differences in their climatic history. It therefore seems possible that there may be some fundamental connection between freezing climates and the local chemical behavior of gold in the weathering cycle. This hypothesis, along with the problematical occurrence of gold as euhedral crystals in arctic gravel and soil placers, has led me to review low temperature phenomena that may bear on the geochemistry of gold. Several effects which may influence the weathering of natural gold-bearing rocks, the chemical complexation of gold, and its subsequent mobility and deposition appear to be strongly connected with freeze action. The exclusion of dissolved solutes, solute gases, and particles from ice, subjects rock and soil minerals to increased corrosion from thin, unfrozen, adsorbed water films which remain at particle surfaces throughout the freezing of rocks and soils. The preferential exclusion of cations (over anions) from growing ice crystals creates charge separations and measurable current flow across waterice phase boundaries in freezing soil — a phenomenon which leads to troublesome seasonal electrolytic corrosion of pipelines buried in soil; this phenomenon may also favor the dissolution of normally insoluble metals such as gold during geologic time periods. The ice-induced accumulation of clays, organic acids, bacteria, and other organic matter at mineral surfaces may also speed chemical attack by providing a nearby sink of alternate cation-binding sites and hence rapid removal of liberated cations from solution. The latter mechanism may be operative in both the dissolution and redeposition of gold. These physical, chemical, and electrical effects are favorable to the dissolution of rocks (in addition to frost shattering) and to the dissolution, mobilization, and redeposition of gold and other noble metals and must therefore contribute significantly to the behavior of gold at low temperatures. The occurrence of large numbers of gold placer deposits in northern Canada, Alaska, and Siberia may thus be due in part to the low temperatures common to these regions.

Precambrian Research↗
USGS1992

Metallogeny of the midcontinent rift system of North America

The 1.1 Ga Midcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ∼ 1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments; (2) sediment-hosted copper sulfide and native copper; (3) copper sulfide veins and lodes hosted by rift-related volcanic and sedimentary rocks; and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Magmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include CuNiPGE and TiFe (V) in the Duluth Complex, U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from country rocks; the interaction between magma and country rocks was important in generation of the magmatic CuNi sulfide deposits. A mantle plume origin has been proposed for the formation of the Midcontinent rift. More than 1 million km 3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift, providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines. These brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume. Hydrothermal deposits were emplaced for at least 30–40 m.y. after rift magmatism and extension ceased. This time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift, or may be due to the timing of post-rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep portions of the rift.

Precambrian Research↗
USGS1993

The hydrothermal-convection systems of kilauea: an historical perspective

Kilauea is one of only two basaltic volcanoes in the world where geothermal power has been produced commercially. Little is known about the origin, size and longevity of its hydrothermal-convection systems. We review the history of scientific studies aimed at understanding these systems and describe their commercial development. Geothermal energy is a controversial issue in Hawai'i, partly because of hydrogen sulfide emissions and concerns about protection of rain forests. ?? 1993.

Geothermics↗
USGS1981

Miocene biochronology and paleoceanography of the North Pacific

Biostratigraphic correlation based on microfossil datum levels, directly or indirectly tied to the paleomagnetic time scale, provides a high resolution time control for the Miocene in the equatorial and middle latitude North Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers, reveal the paleoclimatic and paleoceanographic history. The planktic foraminiferal assemblage change in the early Miocene, extinction of Oligocene fauna and rise of a highly diverse Neogene fauna, appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum-Antarctic circulation. An increase in the siliceous productivity in the eastern equatorial Pacific region between 20 and 18 Ma suggests that the vertical and horizontal circulation was intensified at that time. Climates cooled rapidly during the middle Miocene between 14 and 13 Ma suggesting the growth of a major east Antarctic ice sheet. Paleoclimatic conditions remained generally cool, although oscillating, during the late Miocene. In the late early to middle Miocene faunal provincialism developed between low and middle latitudes, and by late Miocene time a distinct provincialism similar to the present was established.

Marine Micropaleontology↗
USGS1992

Host-rock controlled epigenetic, hydrothermal metasomatic origin of the Bayan Obo REEFe-Nb ore deposit, Inner Mongolia, P.R.C.

Bayan Obo, a complex rare earth element (REE) Fe Nb ore deposit, located in Inner Mongolia, P.R.C. is the world's largest known REE deposit. The deposit is chiefly in a marble unit (H8), but extends into an overlying unit of black shale, slate and schist unit (H9), both of which are in the upper part of the Middle Proterozoic Bayan Obo Group. Based on sedimentary structures, the presence of detrital quartz and algal fossil remains, and the 16-km long geographic extent, the H8 marble is a sedimentary deposit, and not a carbonatite of magmatic origin, as proposed by some previous investigators. The unit was weakly regionally metamorphosed (most probably the lower part of the green schist facies) into marble and quartzite prior to mineralization. Tectonically, the deposit is located on the northern flank of the Sino-Korean craton. Many hypotheses have been proposed for the origin of the Bayan Obo deposit; the studies reported here support an epigenetic, hydrothermal, metasomatic origin. Such an origin is supported by field and laboratory textural evidence; 232 Th/ 208 Pb internal isochron mineral ages of selected monazite and bastnaesite samples; 40 Ar/ 39 Ar incremental heating minimum mineral ages of selected alkali amphiboles; chemical compositions of different generations of both REE ore minerals and alkali amphiboles; and evidence of host-rock influence on the various types of Bayan Obo ores. The internal isochron ages of the REE minerals indicate Caledonian ages for various episodes of REE and Fe mineralization. No evidence was found to indicate a genetic relation between the extensive biotite granitic rocks of Hercynian age in the mine region and the Bayan Obo are deposit, as suggested by previous workers.

Applied Geochemistry↗
USGS1996

Spatial radon anomalies on active faults in California

Radon emanation has been observed to be anomalously high along active faults in many parts of the world. We tested this relationship by conducting and repeating soil air radon surveys with a portable radon meter across several faults in California. The results confirm the existence of fault-associated radon anomalies, which show characteristic features that may be related to fault structures but vary in time due to other environmental changes, such as rainfall. Across two creeping faults in San Juan Bautista and Hollister, the radon anomalies showed prominent double peaks straddling the fault gouge zone during dry summers, but the peak-to-background ratios diminished after significant rain fall during winter. Across a locked segment of the San Andreas fault near Olema, the anomaly has a single peak located several meters southwest of the slip zone associated with the 1906 San Francisco earthquake. Across two fault segments that ruptured during the magnitude 7.5 Landers earthquake in 1992, anomalously high radon concentration was found in the fractures three weeks after the earthquake. We attribute the fault-related anomalies to a slow vertical gas flow in or near the fault zones. Radon generated locally in subsurface soil has a concentration profile that increases three orders of magnitude from the surface to a depth or several meters; thus an upward flow that brings up deeper and radon-richer soil air to the detection level can cause a significantly higher concentration reading. This explanation is consistent with concentrations of carbon dioxide and oxygen, measured in soil-air samples collected during one of the surveys.

Applied Geochemistry↗
USGS1993

Results of interlaboratory comparison of fission track ages for 1992 fission track workshop

Two apatites and one sphene were made available to the fission track research community for analysis prior to the 1992 Fission Track Workshop held in Philadelphia, U.S.A., 13-17 July. Eighteen laboratories throughout the world received aliquots of apatite and sphene. To date, analyses by 33 different scientists have been representing 15 different laboratories. With respect to the previous two interlaboratory comparisons, there is a noticeable improvement in the accuracy of the age results (Naeser and Cebula, 1978; Naeser et al., 1981; Miller et al., 1985;Miller et al.1990). Ninety-four percent of the analysis used the external detector method (EDM) combined with the zeta technique while the remaining individuals used the population method (POP). Track length measurements (requested for the first time in the interlaboratory comparison studies) were in relatively good agreement. ?? 1993.

Nuclear Tracks and Radiation Measurements↗
USGS2014

The environmental and medical geochemistry of potentially hazardous materials produced by disasters

Many natural or human-caused disasters release potentially hazardous materials (HM) that may pose threats to the environment and health of exposed humans, wildlife, and livestock. This chapter summarizes the environmentally and toxicologically significant physical, mineralogical, and geochemical characteristics of materials produced by a wide variety of recent disasters, such as volcanic eruptions, hurricanes and extreme storms, spills of mining/mineral-processing wastes or coal extraction by-products, and the 2001 attacks on and collapse of the World Trade Center towers. In describing these characteristics, this chapter also illustrates the important roles that geochemists and other earth scientists can play in environmental disaster response and preparedness. In addition to characterizing in detail the physical, chemical, and microbial makeup of HM generated by the disasters, these roles also include (1) identifying and discriminating potential multiple sources of the materials; (2) monitoring, mapping, and modeling dispersal and evolution of the materials in the environment; (3) understanding how the materials are modified by environmental processes; (4) identifying key characteristics and processes that influence the materials' toxicity to exposed humans and ecosystems; (5) estimating shifts away from predisaster environmental baseline conditions; and (6) using geochemical insights learned from past disasters to help estimate, prepare for, and increase societal resilience to the environmental and related health impacts of future disasters.

Book chapter↗
USGS2014

Geochemistry of a marine phosphate deposit: A signpost to phosphogenesis

The Permian age Phosphoria Formation in southeastern Idaho and adjoining states represents possibly the largest marine phosphate deposit in the world. The Meade Peak Member, which contains the highest concentrations and amount of carbonate fluorapatite in the formation, was not significantly altered by mechanical reworking during deposition or subsequently by chemical weathering. Thus, its present composition reflects properties of the Phosphoria Sea that were critical to its accumulation and possibly to the accumulation of most major marine phosphate deposits. These properties included the chemistry of the water column, the hydrography, and the level of primary productivity. Calculated accumulation rates of the PO 4 3− and trace nutrients – Cd, Cu, Ni, and Zn – recorded a dynamic upwelling rate of c. 30 m year −1 that supported primary productivity of 2g C m −2 day −1 . High accumulation rates of the hydrogenous redox-sensitive trace metals – Cr, Mo, U, and V – reflect bottom-water redox conditions that were dominantly suboxic, maintained by a balance between the oxidation of ~ 8% of the organic detritus that settled out of the photic zone and advection of bottom water with a residence time of c .10 years. A limited flux into the basin of siliciclastic lithogenous debris contributed further to elevated concentrations of the seawater-derived sediment fractions.

Book chapter↗
USGS2011

The skin: The many functions of fish integument

The integument or skin is the envelope that not only separates and protects a fish from its environment, but also provides the means through which most contacts with the outer world are made. It is a large organ and is continuous with the linings of all body openings, and also covers the fins. Fish integument is a multifunctional organ, and its components may serve important roles in protection, communication, sensory perception, locomotion, respiration, ion regulation, excretion, and thermal regulation.

Book chapter↗
USGS2013

Blending local scale information for developing agricultural resilience in Ethiopia

This brief article looks at the intersection of climate, land cover/land use, and population trends in the world's most food insecure country, Ethiopia. As a result of warming in the Indian and Western Pacific oceans, Ethiopia has experienced substantial drying over the past 20 years. We intersect the spatial pattern of this drying with high resolution climatologies, maps of agricultural expansion, population data, and socioeconomic livelihoods information to suggest that the coincidence of drying and agricultural expansion in south-central Ethiopia is likely adversely affecting a densely populated region with high levels of poverty and low wage levels.

Book chapter↗
USGS2015

Drought monitoring and assessment: Remote sensing and modeling approaches for the Famine Early Warning Systems Network

Drought monitoring is an essential component of drought risk management. It is usually carried out using drought indices/indicators that are continuous functions of rainfall and other hydrometeorological variables. This chapter presents a few examples of how remote sensing and hydrologic modeling techniques are being used to generate a suite of drought monitoring indicators at dekadal (10-day), monthly, seasonal, and annual time scales for several selected regions around the world. Satellite-based rainfall estimates are being used to produce drought indicators such as standardized precipitation index, dryness indicators, and start of season analysis. The Normalized Difference Vegetation Index is being used to monitor vegetation condition. Several satellite data products are combined using agrohydrologic models to produce multiple short- and long-term indicators of droughts. All the data sets are being produced and updated in near-real time to provide information about the onset, progression, extent, and intensity of drought conditions. The data and products produced are available for download from the Famine Early Warning Systems Network (FEWS NET) data portal at http://earlywarning.usgs.gov . The availability of timely information and products support the decision-making processes in drought-related hazard assessment, monitoring, and management with the FEWS NET. The drought-hazard monitoring approach perfected by the U.S. Geological Survey for FEWS NET through the integration of satellite data and hydrologic modeling can form the basis for similar decision support systems. Such systems can operationally produce reliable and useful regional information that is relevant for local, district-level decision making.

Book chapter↗
USGS2019

Contemporary human impacts on alpine ecosystems: the direct and indirect effects of human-induced climate change and land use

Alpine ecosystems account for ca. 3 % of terrestrial habitats yet, along with adjacent mountain systems, provide water resources to nearly half of the world’s human population. Approximately 20 % of humans live in or near mountain areas, making it inherently important to understand current impacts on these systems. Here, I review literature regarding current and projected human impacts on alpine ecosystems, including the direct and indirect impacts of human-induced climate change on alpine plant, animal, and soil communities. I also discuss the influence of recreation and tourism, grazing, and other land use changes including the introduction of non-native and invasive species in alpine systems. I conclude with management implications as well as future areas of research needed to better understand changes to these systems.

Book chapter↗
USGS2018

Sirenian life history

Sirenians, including the manatees and dugongs, are large herbivorous mammals that have evolved to an aquatic form since the Eocene epoch. Sirenians have unique adaptations, including dense bone for ballast and a longitudinal hemidiaphragm separating paired lungs (which aid in maintaining a horizontal posture in the water column), species-specific rostral deflection, and unique dentition for specialized feeding, which all contribute to their success. All sirenians produce one calf per breeding cycle and have long calf-dependency periods. Low reproduction rates are common for long-lived, large mammals, but may compromise their existence in today’s quickly changing world today. All sirenian populations are listed as either threatened or endangered, and some local stocks have been completely extirpated by human activities.

Book chapter↗
USGS2018

Chiroptera

With over 1200 species identified, bats represent almost one quarter of the world’s mammals. Bats provide crucial environmental services, such as insect control and pollination, and inhabit a wide variety of ecological niches on all continents except Antarctica. Despite their ubiquity and ecological importance, relatively little has been published on diseases of bats, while much has been written on bats’ role as reservoirs in disease transmission. This chapter will focus on diseases and pathologic processes most commonly reported in captive and free-ranging bats. Unique anatomical and histological features and common infectious and non-infectious diseases will be discussed. As recognition of both the importance and vulnerability of bats grows, particularly following population declines in North America due to the introduction of the fungal disease white-nose syndrome, efforts should be made to better understand threats to the health of this unique group of mammals.

Book chapter↗
USGS2022

Societal values of inland fishes

a. Aim: To demonstrate the societal values of inland fishes through nine services provided by inland fishes. Each service is defined, key stakeholders identified, and threats enumerated. Diverse case studies (geography, taxonomy, fishery-type) provide examples to highlight the societal values around the world. b. Main concepts: Nine societal services of inland fishes – 1. Livelihoods and subsistence income; 2. Commercial income; 3. Food and nutrition; 4. Recreational services; 5. Cultural services; 6. Educational and scientific opportunities within fisheries; 7. Biodiversity and ecosystem function; 8. Regulation and indicator of freshwater quality ; and 9. Regulation of freshwater quantity and natural flow regimes. c. Conclusion/outlook: Inland fishes have immense social, economic, and ecological importance. Freshwater ecosystems face a diverse array of pressures that threaten the fulfillment of societal services. Addressing key knowledge gaps can assist with sustainable management and conservation of these important resources.

Book chapter↗