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At least 1,729 records · Page 96Linked to original sources
USGS1979

Geology and industrial mineral resources of the Macon-Gordon kaolin district, Georgia

The Macon-Gordon kaolin district is about 80 miles (130 km) southeast of Atlanta, Georgia. It extends across the boundary between, and includes parts of, the Piedmont and Atlantic Coastal Plain physiographic provinces. The rocks in the Piedmont are mainly intensely folded sericite schist and granite gneiss containing irregular masses of amphibolite and feldspathic biotite gneiss and scattered igneous intrusive rocks. Most of the crystalline rocks are thought to be of Paleozoic age, but some of the intrusive rocks may be younger. The crystalline rocks are cut by a major unconformity and are overlain by sedimentary formations ranging in age from Cretaceous to Miocene. The valuable kaolin deposits occur in the Cretaceous beds, undivided, and in the Huber Formation which is of Paleocene to middle Eocene age. The resources of kaolin in the district are estimated in millions of metric tons as follows: reserves, 100; subeconomic resources, 700 to 900; undiscovered resources, probably 700 to 1,000. In addition to kaolin, the leading mineral commodity mined in the district, crushed stone and sand are now being produced, and fuller's earth and a minor amount of limestone were formerly produced. The crushed stone is quarried from igneous rocks in the Piedmont province. The sand is washed from the Cretaceous beds, undivided. The fuller's earth was mined from the Twiggs Clay Member of the Barnwell Formation, and limestone was dug from the Tivola Limestone.

Georgia↗
USGS1980

U.S. Geological Survey role in earthquake prediction

Work in the Seismology Branch on the problem of earthquake prediction is based primarily on the recording and analysis of seismic (elastic) waves in the Earth generated either by earthquakes themselves or by artificial sources such as quarry blasts or explosions detonated in drill holes. At the present time this work is still very much a research effort focused largely on earthquake occurrence within the San Andreas fault system and related faults in California. Major aspects of this research include 1) studies of the spatial-temporal patterns of earthquake occurrence as a basis for recognizing distinctive sequences of events that may precede moderate-to-large earthquakes, 2) studies of Earth structure as a basis for the accurate location of earthquake hypocenters and understanding the physical properties and state of active fault zones, and 3) studies of the earthquake source mechanisms as a basis for recognizing possible variations in stress-drop, rupture direction, and so on that may precede moderate-to-large earthquakes.

California↗
USGS1980

Holocene geomagnetic secular variation in the western United States: implications for the global geomagnetic field

A record of Holocene geomagnetic secular variation in the western 14 United States has been measured from volcanic rocks dated by 14 C. Analysis of errors associated with the paleomagnetic techniques used suggests that all laboratory measurement errors are smaller than those introduced by deformation of the volcanic units and the errors of orientation of cores in the field. The dispersion in the calculated virtual geomagnetic poles introduced by the geographic spread of sample localities around the western United States is less than the average uncertainty from an individual locality, about 2 deg. The history of secular variation of field direction in the western United States has been reconstructed where sufficient time control exists. This history can be approximately reconstructed for the past 3000 years; in this time period, inclination varied from 44 to 72 deg and declination varied from 344 to 22 deg. These variations of the local field direction have periods between 500 and 1500 years. Prior to 3000 years B.P., the available observations allow reconstruction of the secular variation history only for short time intervals. The mean VGP obtained from paleofield directions measured from 77 volcanic units of Holocene and late Pleistocene age in the western United States does not coincide with the geographic pole of the Earth, but is displaced 2.5 deg from the geographic pole in a direction away from the sampled region. This displacement is just at the limit of significance at 95 percent confidence. Using a 10 -5 torr vacuum furnace, paleointensities have been obtained by the Thelliers' method from both high-temperature oxidized and unoxidized basic volcanic rocks. Specimens which have undergone incomplete high-temperature oxidation in nature commonly fail the Thellier experiment; the relationship between NRM lost and TRM gained in a known magnetic field is not linear. Despite the vacuum, oxidation can still occur above 300°C in the furnace ovens. The best determinations of paleointensity come from specimens in which the remanence resides primarily in single phase titanomagnetite or in intergrowths of Ti-poor magnetite in ilmenite which have been formed by natural high-temperature oxidation. Paleointensity determined from these specimens varies from 0.364 x 10 -4 T to 0.865 x 10 -4 T (1.0 x 10 -4 T = 1 0e); the period of oscillation of paleointensity is about 500 to 1000 years. Close agreement has been found between the paleointensity measurements from this study and those from archeomagnetic studies in the southwestern United States. The similarity of the periods of intensity variation to those of field direction changes may indicate that variations of the nondipole components of the geomagnetic field dominate both. By combining paleomagnetic and archeomagnetic data from globally distributed localities, the magnetic dipole can be shown to have wobbled with a period as short as 2000 years. Local variation of the field can be described as the consequence of fluctuation of the dipole moment, wobble of the dipole, and longitudinal drift of a nondipole field similar to that of the present. During the Holocene, the dipole moment of the Earth has fluctuated with a period of approximately 8000 years, though when viewed from a single region, the fluctuation of the dipole moment is obscured by variation of nondipole components of the field.

Open-File Report↗
USGS1981

Paleomagnetic study of the As Sarat volcanic field, southwestern Saudi Arabia

Four stratigraphic sections through alkali basalt flows of Oligocene-Miocene age (24 to 29 m.y.) in the As Sarat volcanic field, southwestern Saudi Arabia, were sampled for paleomagnetic study. Forty-two magnetically acceptable flows (139 samples) yield a mean direction of magnetization of D=-4.7°, 1=15.2° ( α 95=4.3°), which defines a paleomagnetic pole at 78.8°N, 247.8°E. Of these acceptable flows, 24 are normally magnetized and 18 are reversed. Parts of two sections of flows erupted apparently during the early phases of a polarity reversal of the earth's field. Although the mean paleomagnetic directions determined from each flow do not collectively define a strict Fisherian distribution, the fact that the mean directions for each of the four sections are nearly identical indicates that the overall paleomagnetic pole position is reliable. The magnetostratigraphy can be only generally correlated from one section to another apparently because of a lateral thickening and pinching out of many flows between sections. The dispersion of directions due to secular variation of the upper Oligocene and lower Miocene field (standard angular deviation = 16.2°) is about the same as that produced by the recent field. If the rate of secular change during the time of As Sarat eruption was approximately that of the present, the rate of eruption during several sequences of As Sarat flows is estimated to be one flow about every 100 years. The fact that the mean direction derived from 24 normally magnetized flows is significantly different from that derived from the 18 reversed flows supports the hypothesis of a displaced dipole source for the earth's field in late Oligocene to early Miocene time. The results from As Sarat, as well as those from Aden, compared with paleomagnetic results from Late Tertiary rocks in Africa indicate with 95 percent confidence that the Red Sea has opened at least 2° in the past 5 m.y., and at least 4° in the past 25 m.y. The paleomagnetic results also indicate that the Arabian Peninsula was more equatorial in late Oligocene to early Miocene time than it is now, by an amount compatible with the opening of the Gulf of Aden.

As Sarat volcanic field↗
USGS1982

Diatremes of the Hopi Buttes, Arizona; chemical and statistical analyses

Lacustrine sediments deposited in maar lakes of the Hopi Buttes diatremes are hosts for uranium mineralization of as much as 1500 ppm. The monchiquites and limburgite turfs erupted from the diatremes are distinguished from normal alkalic basalts of the Colorado Plateau by their extreme silica undersaturation and high water, TiO2, and P2O5 contents. Many trace elements are also unusually abundant, including Ag, As, Ba, Be, Ce, Dy, Eu, F, Gd, Hf, La, Nd, Pb, Rb, Se, Sm, Sn, Sr, Ta, Tb, Th, U, V, Zn, and Zr. The lacustrine sediments, which consist predominantly of travertine and clastic rocks, are the hosts for syngenetic and epigenetic uranium mineralization of as much as 1500 ppm uranium. Fission track maps show the uranium to be disseminated within the travertine and clastic rocks, and although microprobe analyses have not, as yet, revealed discrete uranium-bearing phases, the clastic rocks show a correlation of high Fe, Ti, and P with areas of high U. Correlation coefficients show that for the travertines, clastics, and limburgite ruffs, Mo, As, Sr, Co, and V appear to have the most consistent and strongest correlations with uranium. Many elements, including many of the rare-earth elements, that are high in these three rocks are also high in the monchiquites, as compared to the average crustal abundance for the respective rock type. This similar suite of anomalous elements, which includes such immobile elements as the rare earths, suggests that Fluids which deposited the travertines were related to the monchiquitic magma. The similar age of about 5 m.y. for both the lake beds and the monchiquites also appears to support this source for the mineralizing fluids.

Open-File Report↗
USGS1986

Red-Sea rift magmatism near Al Lith, Kingdom of Saudi Arabia

A newly recognized Tertiary dike complex and comagmatic volcanic rocks exposed on the central Saudi Arabian coastal plain record early stages of magmatism related to Red Sea rifting. Intrusive and stratigraphic relationships, and new potassium-argon dating indicate episodic magmatism from about 30 Ma to the present. Additional stratigraphic and radiometric evidence suggests that limited rift-related magmatism may have began as early as about 50 Ma ago. An early phase of crustal extension in the region was accompanied by faulting and graben formation and by dike-swarm intrusion. The style of extension and intrusion changed approximately 20 Ma ago. Localized volcanism and sheeted dike injection ceased and were replaced by the intrusion of thick gabbro dikes. This change may mark the onset of sea-floor spreading in the central Red Sea. The dikes and volcanic rocks consist of a bimodal mafic-felsic suite with transitional subalkaline to alkaline chemistry. Although no unique petrogenetic model can be developed for the suite, the following observations and conclusions are apparent from the available reconnaissance geochemistry: 1) Strontium isotopic initial ratios overlap in the range 0.7031 to 0.7047 and are not clearly related to alkalinity or silica content. Therefore, the bimodality and alkalinity of the suite are not products of contamination by the radiogenic Precambrian upper-crustal granitic rocks exposed in the region. 2) Several of the evolved rocks (rhyolites and comendite) show large to extreme negative europium anomalies and heavy rare-earth element (HREE) enrichment, features that cannot be explained by low-pressure crystal fractionation of potential parent magmas. An intriguing possibility is that HREE enrichments and large negative Eu anomalies of some peraluminous rhyolites (and granites) may result from the complete melting of garnet from middle or lower crustal rocks. 3) Most of the basalts are light rare-earth element (LREE)-enriched, consistent with derivation from fertile mantle in a continental-rift setting, however, interaction of the mafic melts with lower continental crust cannot be ruled out. A model of poly-baric mantle-melt derivation, producing several alkalinesubalkaline cycles, best explains magmatism in the Red Sea region. Differences in the depths and dynamics of mantle-melt extraction and transport brought about through changes in crust and mantle structure as the rift and paar developed may account for the transition from mixed alkaline-subalkaline bimodal magmatism of the pre-20 Ma rift basin to exclusively subalkaline (tholeiitic) magmatism at the Red Sea spreading axis and to predominantly alkali basalt volcanism within the Arabian Shield.

Open-File Report↗
USGS1990

A numerical study of some potential sources of error in side-by-side seismometer evaluations

This report presents the results of a series of computer simulations of potential errors in test data, which might be obtained when conducting side-by-side comparisons of seismometers. These results can be used as guides in estimating potential sources and magnitudes of errors one might expect when analyzing real test data. First, the derivation of a direct method for calculating the noise levels of two sensors in a side-by-side evaluation is repeated and extended slightly herein. This bulk of this derivation was presented previously (see Holcomb 1989); it is repeated here for easy reference. This method is applied to the analysis of a simulated test of two sensors in a side-by-side test in which the outputs of both sensors consist of white noise spectra with known signal-tonoise ratios (SNR's). This report extends this analysis to high SNR's to determine the limitations of the direct method for calculating the noise levels at signal-to-noise levels which are much higher than presented previously (see Holcomb 1989). Next, the method is used to analyze a simulated test of two sensors in a side-by-side test in which the outputs of both sensors consist of bandshaped noise spectra with known signal-tonoise ratios. This is a much more realistic representation of real world data because the earth's background spectrum is certainly not flat. Finally, the results of the analysis of simulated white and bandshaped side-by-side test data are used to assist in interpreting the analysis of the effects of simulated azimuthal misalignment in side-by-side sensor evaluations. A thorough understanding of azimuthal misalignment errors is important because of the physical impossibility of perfectly aligning two sensors in a real world situation. The analysis herein indicates that alignment errors place lower limits on the levels of system noise which can be resolved in a side-by-side measurement It also indicates that alignment errors are the source of the fact that real data noise spectra tend to follow the earth's background spectra in shape.

Open-File Report↗
USGS1994

Bibliography of U.S. Geological Survey water-resources reports for Utah

This bibliography contains a complete listing of reports prepared by personnel of the U.S. Geological Survey from 1886 through December 31, 1993, that discuss the water resources of Utah. The reports were prepared primarily by personnel of the Water Resources Division, Utah District, in cooperation with State, other Federal, and local agencies. Several reports were prepared as a part of studies directly funded by the U.S. Geological Survey, and several were prepared by contractors for the U.S. Geological Survey. The bibliography is divided into three major parts: (1) publications of the U.S. Geological Survey; (2) publications prepared by the U.S. Geological Survey in cooperation with and published by agencies of the State of Utah; and (3) reports printed in other publications reports prepared by the U.S. Geological Survey but published by other agencies or by professional organizations. Publications of the U.S. Geological Survey still in print may be purchased from the U.S. Geological Survey, Earth Science Information Center, Open-File Reports Section, Box 25286, MS 517, Denver Federal Center, Denver, Colorado 80225. Publications that are out of print at the time of this compilation are marked with an asterisk (*). Except for water-supply papers, most publications that are out of print and unavailable for purchase may be examined at the U.S. Geological Survey Earth Science Information Center, 2222 West 2300 South, 2nd Floor, Salt Lake City, Utah 84119. Reports published by the Utah Department of Natural Resources, Divisions of Water Rights and Water Resources, are available on request from these agencies or from the U.S. Geological Survey, Water Resources Division, Room 1016 Administration Building, 1745 West 1700 South, Salt Lake City, Utah 84104. Water-Resources Bulletins of the Utah Geological Survey may be purchased from that agency at 2363 Foothill Drive, Salt Lake City, Utah 84109-1491. Inquiries as to the availability of reports listed as "reports printed in other publications" must be addressed to the professional organization or agency that published them. Most of these reports are available in larger libraries, such as the library of the University of Utah. Most open-file reports are available for inspection at the U.S. Geological Survey, Water Resources Division, Room 1016 Administration Building, 1745 West 1700 South, Salt Lake City, Utah 84104. A small number of the open-file reports that have been duplicated as Utah basic- (or hydrologic-) data reports are free on request. An index is included in this bibliography for ease of reference. Water-supply papers on the quantity and quality of ground and surface water in Utah that were published in a series are not listed separately in the index but are presented in tables 1 to 4.

Utah↗
USGS1996

USGS response to an urban earthquake, Northridge '94

The urban centers of our Nation provide our people with seemingly unlimited employment, social, and cultural opportunities as a result of the complex interactions of a diverse population embedded in an highly-engineered environment. Catastrophic events in one or more of the natural earth systems which underlie or envelop urban environment can have radical effects on the integrity and survivability of that environment. Earthquakes have for centuries been the source of cataclysmic events on cities throughout the world. Unlike many other earth processes, the effects of major earthquakes transcend all political, social, and geomorphic boundaries and can have decided impact on cities tens to hundreds of kilometers from the epicenter. In modern cities, where buildings, transportation corridors, and lifelines are complexly interrelated, the life, economic, and social vulnerabilities in the face of a major earthquake can be particularly acute. The 1994 Northridge Earthquake was a major test for parts of what many consider the most earthquake-prepared and best-engineered metropolitan region in the United States. While the combined efforts of concerned professionals at all levels of government, academia, and the private sector have produced significant advances in our knowledge of the causes and potential effects of earthquakes, and of ways to reduce their impact, it remains unfortunately true that actual earthquakes provide important opportunities to test those advances in our knowledge. In the hours and days following the Northridge Earthquake, the four Federal member agencies of the National Earthquake Hazards Reduction Program (NEHRP), the Federal Emergency Management Agency (FEMA), the National Institute for Standards and Technology (NIST), the National Science Foundation (NSF), and the United States Geological Survey (USGS) laid out a detailed plan for collecting, analyzing, archiving, and reporting information that would benefit the Nation in future earthquake hazards reduction efforts. Congress provided a special appropriation to FEMA to carry out this plan and FEMA distributed those funds to the four NEHRP agencies. The USGS was responsible for conducting geophysical and geological investigations in support of the NEHRP Post-earthquake Study. For the past 2 years, the USGS has rigorously pursued over 40 tasks focused on the USGS Northridge Earthquake Mission. This document is a summary report of the USGS findings; additional technical reports on specific USGS tasks are appearing in various scientific journals and USGS publications.

California↗
USGS1998

Digital Geologic Map of the Rosalia 1:100,000 Quadrangle, Washington and Idaho: A Digital Database for the 1990 S.Z. Waggoner Map

The geologic map of the Rosalia 1:100,000-scale quadrangle was compiled in 1990 by S.Z. Waggoner of the Washington state Division of Geology and Earth Resources. This data was entered into a geographic information system (GIS) as part of a larger effort to create regional digital geology for the Pacific Northwest. The intent was to provide a digital geospatial database for a previously published black and white paper geologic map. This database can be queried in many ways to produce a variety of geologic maps. Digital base map data files are not included: they may be obtained from a variety of commercial and government sources. This database is not meant to be used or displayed at any scale larger than 1:100,000 (e.g., 1:62,500 or 1:24,000) as it has been somewhat generalized to fit the 1:100,000 scale map. The map area is located in eastern Washington and extends across the state border into western Idaho. This open-file report describes the methods used to convert the geologic map data into a digital format, documents the file structures, and explains how to download the digital files from the U.S. Geological Survey public access World Wide Web site on the Internet. We wish to thank J. Eric Schuster of the Washington Division of Geology and Earth Resources for providing the original stable-base mylar and the funding for it to be scanned. We also thank Dick Blank and Barry Moring of the U.S. Geological Survey for reviewing the manuscript and digital files, respectively.

Open-File Report↗
USGS1998

Experimental investigations regarding the use of sand as an inhibitor of air convection in deep seismic boreholes

Tilt has been the nemesis of horizontal long period seismology since its inception. Modern horizontal long period seismometers with their long natural periods are incredibly sensitive to tilt. They can sense tilts smaller than 10 -11 radians. To most readers, this is just a very very small number, so we will begin with an example, which should help to illustrate just how small 10 -11 radians is. Suppose we have an absolutely rigid rod which is approximately 4170 kilometers long; this just happens to be the Rand McNally map scaled crow flight distance between Los Angeles and Boston. Tilting this rod 10 -11 radians corresponds to raising one end of the rod 0.0000417 meters. Alas, this is just another very very small number! However, this corresponds to slipping a little less than one third a sheet of ordinary copying paper under one end of this perfectly rigid rod. To clarify, we mean, take a sheet of paper just like the paper this report is printed on and split it a little less than one third in the thickness direction, then put it under the end of the 4170 kilometer long rod! This will tilt the rod 10 -11 radians. Real world seismometers are nowhere near the length of this rod. A KS-54000 is about two meters long. Tilting a rod only two meters long 10~n radians corresponds to moving one end of this rod a mere 0.00000000002 meters or 0.02 millimicrons. As one of the authors old math teachers used to say, "That's PDS" (PDS = Pretty Damn Small). Unfortunately, the long period seismologist does not have the luxury of ignoring PDS numbers when it suits him as the mathematician frequently does. He must live in the real world in which tilts this small create severe contamination of long period seismic data. At periods longer than 20 seconds, tilt noise contaminates the long period data from all instruments installed on or near the earth's surface. Many years of experimentation revealed that installing the sensors at depth in deep mines drastically reduced the level of tilt noise in long period data. However, low levels of tilt noise persisted even at great depth; this noise was caused by air convection in the vault in which the sensors were installed. Over the years, methods were developed to control the air motion with mechanical barriers (boxes) around the sensors and by stratifying (creating a situation in which the air temperature increases with height) the air in the vault near the seismometer. These methods decreased tilt noise in deep mines to very low levels. However, deep mines, that are economically and environmentally suitable and accessible to seismology, are not plentiful and are not evenly distributed over the earth's surface. Therefore, the borehole deployable Teledyne Geotech KS-36000 and later the KS-54000 sensor systems were developed to fulfill the need for instruments that could be installed at depth wherever high quality long period data was desired. Early in the development program, it became evident to the Teledyne Geotech personnel that air convection within the borehole was going to be a significant problem in KS deployments. Experimental and theoretical investigations conducted by Teledyne Geotech (see Douze and Sherwin, 1975, and Sherwin and Cook, 1976) produced a list of recommended installation procedures for reducing the effects of air convection. These procedures consisted of wrapping the sensor in a relatively thin layer of foam insulation, filling the free space volume in the vicinity of the centralizer-bail assembly with foam insulation, and the installation of styrofoam hole plugs immediately above the cable strain relief assembly at the top of the sensor package and at the top of the borehole. This technology has performed quite satisfactorily for over 20 years but evidence of tilt noise in the system output has persisted throughout the KS deployment program (the evidence was that the horizontal components were usually noisier than the vertical components) even in deep boreholes. Some deep borehole sites have been plagued by quite high levels of horizontal noise. Therefore, there has been a definite need for a new technique for controlling low level tilt noise in deep boreholes and the use of sand has been under consideration for several years. Figure 1 contains conceptual illustrations of both the conventional holelock installed KS sensor system and the same sensor installed in sand. This figure demonstrates the major differences between the two installation methods. The curved arrows in the borehole on the left in the figure denote possible air convection cells which are believed to be the source of tilt noise in some of the conventional installations. This air motion is eliminated in a sand installation by filling most of the free air volume surrounding the seismometer with sand as shown in the right hand portion of the figure. The sand actually performs two functions; it prevents air motion and provides a remarkably ridgid clamping of the seismometer in the borehole. This report presents the results of quantitative experimental investigations into the effectiveness of controlling low level air convection in seismic borehole installations with sand. The main body of the experimental effort consisted of installing two KS-540001 sensor systems in closely spaced shallow boreholes, allowing the sensors to reach equilibrium operation, and then pouring sand into both boreholes to observe any changes caused by pouring sand into the holes. The hypothesis of the experiment was that the sand would fill up the entire free air volume between the sensor package and the borehole walls thereby preventing movement of the air in the vicinity of the sensor package. The validity of this hypothesis had been qualitatively proven by earlier experiments at ASL and by the sand installations at the IRIS/ASL stations ANMO in 1995 and COLA in 1996. This experiment documents the degree of improved noise levels to be expected if KS instruments are installed in sand instead of in the conventional manner.

Open-File Report↗
USGS1999

U.S. Geological Survey programs in Florida, 1999

The safety, health, and economic well-being of Florida?s citizens are important to the U.S. Geological Survey (USGS), which is involved in water-related, geologic, biological, land use, and mapping issues in many parts of the State. The USGS office in Tallahassee acts as the liaison for all studies conducted by USGS scientists in Florida. Water resources activities are conducted not only from the office in Tallahassee, but also from offices in Miami, Tampa, and Altamonte Springs (Orlando). Scientists in these offices investigate surface water, ground water and water quality in Florida, working in cooperation with other Federal, State and local agencies and organizations. The USGS Center for Coastal Geology and Regional Marine Studies was established in St. Petersburg in 1988, in cooperation with the University of South Florida. The Center conducts a wide variety of research on mineral resources and on coastal and regional marine problems, including coastal erosion, climate change, wetlands deterioration, and coastal pollution. A USGS mapping office is located in St. Petersburg. Also, the Earth Science Information Center (ESIC) in Tallahassee provides USGS information to customers and directs inquiries to the appropriate USGS office or State agency on earth science topics, particularly those related to cartography, geography, aerial photography, and digital data. Biologists at the USGS Florida Caribbean Science Center, located in Gainesville, conduct biological and ecosystem studies in Florida, Puerto Rico, and the Virgin Islands.

Florida↗
USGS1999

Publications of the Western Geologic Mapping Team 1997-1998

The Western Geologic Mapping Team (WGMT) of the U.S. Geological Survey, Geologic Division (USGS, GD), conducts geologic mapping and related topical earth-science studies in the western United States. This work is focused on areas where modern geologic maps and associated earth-science data are needed to address key societal and environmental issues such as ground-water quality, potential geologic hazards, and land-use decisions. Areas of primary emphasis currently include southern California, the San Francisco Bay region, the Pacific Northwest, the Las Vegas urban corridor, and selected National Park lands. The team has its headquarters in Menlo Park, California, and maintains smaller field offices at several other locations in the western United States. The results of research conducted by the WGMT are released to the public as a variety of databases, maps, text reports, and abstracts, both through the internal publication system of the USGS and in diverse external publications such as scientific journals and books. This report lists publications of the WGMT released in calendar years 1997 and 1998. Most of the publications listed were authored or coauthored by WGMT staff. However, the list also includes some publications authored by formal non-USGS cooperators with the WGMT, as well as some authored by USGS staff outside the WGMT in cooperation with WGMT projects. Several of the publications listed are available on the World Wide Web; for these, URL addresses are provided. Most of these Web publications are USGS open-file reports that contain large digital databases of geologic map and related information. For these, the bibliographic citation refers specifically to an explanatory pamphlet containing information about the content and accessibility of the database, not to the actual map or related information comprising the database itself.

Open-File Report↗
USGS1999

Geometry, structure, and concealed lithology of the San Rafael Basin, southeastern Arizona

The contiguous United States has been well explored for exposed conventional mineral deposits. Therefore, it is likely that many economically viable and strategically significant conventional undiscovered mineral deposits will be found in bedrock concealed beneath basin sediments. Mineral resource assessments must incorporate an understanding of the geometry, structure, and concealed lithology of basins in order to be accurate. This report presents an analysis of the basin geometry and structure of the San Rafael basin in southeastern Arizona. In addition, a new methodology for inferring concealed lithology is presented and applied in the San Rafael basin. Gravity data is used to model the geometry of the basin using recent models of sediment density vs. depth developed in the region. This modeling indicates that the basin has a maximum depth of approximately 1.05 km plus or minus 0.10 km. In the southern portion, the basin can be modeled as an asymmetric graben faulted on the western margin. The northern portion of the basin is structurally more complex and may have high angle faults on the western, northern, and eastern margin. Near-ground closely spaced Earth’s total intensity magnetic field data is used to locate concealed faults within the basin. This data is also used to infer lithology concealed by shallow basin sediments. Airborne Earth’s total intensity magnetic field data is used to help infer concealed lithology in deep portions of the basin. The product of integrating all data and interpretations is a map which presents the geometry of the basin, faults and contacts concealed by basin sediments, and an estimate of the bedrock lithology concealed by basin sediment. Based on basin geometry and concealed lithology, the San Rafael basin has a high potential for concealed mineral deposits on its western and northern margin. In particular, a newly discovered magnetic anomaly in the northern portion of the basin can be modeled as a granitic intrusion with highly altered margins and may represent a potential mineral resource target. Based on the permeability and porosity of upper basin fill found in nearby basins, the San Rafael basin may contain an aquifer up to 300 meters thick over a substantial area of the basin.

Arizona↗
USGS1980

Lunar remote sensing and measurements

Remote sensing and measurements of the Moon from Apollo orbiting spacecraft and Earth form a basis for extrapolation of Apollo surface data to regions of the Moon where manned and unmanned spacecraft have not been and may be used to discover target regions for future lunar exploration which will produce the highest scientific yields. Orbital remote sensing and measurements discussed include (1) relative ages and inferred absolute ages, (2) gravity, (3) magnetism, (4) chemical composition, and (5) reflection of radar waves (bistatic). Earth-based remote sensing and measurements discussed include (1) reflection of sunlight, (2) reflection and scattering of radar waves, and (3) infrared eclipse temperatures. Photographs from the Apollo missions, Lunar Orbiters, and other sources provide a fundamental source of data on the geology and topography of the Moon and a basis for comparing, correlating, and testing the remote sensing and measurements. Relative ages obtained from crater statistics and then empirically correlated with absolute ages indicate that significant lunar volcanism continued to 2.5 b.y. (billion years) ago-some 600 m.y. (million years) after the youngest volcanic rocks sampled by Apollo-and that intensive bombardment of the Moon occurred in the interval of 3.84 to 3.9 b.y. ago. Estimated fluxes of crater-producing objects during the last 50 m.y. agree fairly well with fluxes measured by the Apollo passive seismic stations. Gravity measurements obtained by observing orbiting spacecraft reveal that mare basins have mass concentrations and that the volume of material ejected from the Orientale basin is near 2 to 5 million km 3 depending on whether there has or has not been isostatic compensation, little or none of which has occurred since 3.84 b.y. ago. Isostatic compensation may have occurred in some of the old large lunar basins, but more data are needed to prove it. Steady fields of remanent magnetism were detected by the Apollo 15 and 16 subsatellites, and the lunar dipole field was revised to no more than 6x 10 19 gauss. High-resolution mapping of fields of weak remanent magnetism (to 0.1 gamma) was made possible by the Apollo plasma and energetic-particle experiment. Although the causes of remanent magnetism are poorly understood, correlations with geologic units suggest the results may ultimately have farreaching significance to lunar history. Maria are much less structured by strong surface magnetic anomalies than the highlands. The strongest anomalies are associated with ejecta of farside basins, plains materials filling pre-Imbrian craters, and other old Imbrian to pre-Imbrian units. The high remanent fields could be due to cooling of ejecta units in an ancient magnetic field, lunar regolith maturity, extensive reworking and disruption of a magnetized layer, or simply surface roughness. Orbital geochemical experiments have shown that lunar high lands have larger Al: Si ratios and smaller Mg: Si ratios than maria. These two ratios are inversely related on a regional basis. With the exception of fresh craters, albedo and Al : Si ratios vary directly, showing that compositional differences as well as exposure of fresh materials are responsible for high albedos. Statistically treated data show that geologic contacts and compositional boundaries are concentric and can be roughly matched. Some craters on mare material have penetrated the mare fill, bringing highland-type materials to the surface. Natural radioactivity from thorium, potassium, and uranium is inversely correlated with elevation. Mare regions are enriched in iron, titanium, and magnesium relative to the highlands. Orbital bistatic-radar results provide estimates of surface roughness at two scale lengths (about 30 m and 250 m), which agree with visual estimates of roughness. The dielectric constant of the lunar surface, where sampled, is uniform to 13-cm radar and near 3. Slope frequency distributions measured by the radar vary and

Professional Paper↗
USGS1978

Rock pushing and sampling under rocks on Mars

Viking Lander 2 acquired samples on Mars from beneath two rocks, where living organisms and organic molecules would be protected from ultraviolet radiation. Selection of rocks to be moved was based on scientific and engineering considerations, including rock size, rock shape, burial depth, and location in a sample field. Rock locations and topography were established using the computerized interactive video-stereophotogrammetric system and plotted on vertical profiles and in plan view. Sampler commands were developed and tested on Earth using a full-size lander and surface mock-up. The use of power by the sampler motor correlates with rock movements, which were by plowing, skidding, and rolling. Provenance of the samples was determined by measurements and interpretation of pictures and positions of the sampler arm. Analytical results demonstrate that the samples were, in fact, from beneath the rocks. Results from the Gas Chromatograph-Mass Spectrometer of the Molecular Analysis experiment and the Gas Exchange instrument of the Biology experiment indicate that more adsorbed(?) water occurs in samples under rocks than in samples exposed to the sun. This is consistent with terrestrial arid environments, where more moisture occurs in near-surface soil un- der rocks than in surrounding soil because the net heat flow is toward the soil beneath the rock and the rock cap inhibits evaporation. Inorganic analyses show that samples of soil from under the rocks have significantly less iron than soil exposed to the sun. The scientific significance of analyses of samples under the rocks is only partly evaluated, but some facts are clear. Detectable quantities of martian organic molecules were not found in the sample from under a rock by the Molecular Analysis experiment. The Biology experiments did not find definitive evidence for Earth-like living organisms in their sample. Significant amounts of adsorbed water may be present in the martian regolith. The response of the soil from under a rock to the aqueous nutrient in the Gas Exchange instrument indicates that adsorbed water and hydrates play an important role in the oxidation potential of the soil. The rock surfaces are strong, because they did not scratch, chip or spall when the sampler pushed them. Fresh surfaces of soil and the undersides of rocks were exposed so that they could be imaged in color. A ledge of soil adhered to one rock that tilted, showing that a crust forms near the surface of Mars. The reason for low amounts of iron in the sampIes from under the rocks is not known at this time.

Professional Paper↗
USGS2000

Geologic studies in Alaska by the U.S. Geological Survey, 1997

The eight papers that follow continue the series of U.S. Geological Survey (USGS) reports on investigations in the geologic sciences in Alaska. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science information in Alaska. The papers in this volume are organized under the topics Resources, Geologic Framework, and Environment and Climate. Such an organization is intended to reflect the scope and objectives of USGS programs currently active in Alaska. Resource papers include one that presents detailed observations from a Mississippian Zn-Pb-Cu-Ag occurrence in the Brooks Range (Werdon). Mineralogic, chemical, and isotopic data provide the basis for a proposed relationship between this vein-breccia deposit and the shale-hosted massive sulfide deposit type, which includes the active Red Dog mine in the western Brooks Range. Also included under the topic of Resources is a paper that presents geochemical and isotopic data from the Greens Creek and Woewodski Island volcanogenic massive sulfide deposits in southeastern Alaska (Newberry and Brew). The depositional environment and sedimentological setting of Tertiary coal beds in the Matanuska and Susitna Valleys is the focus of a third paper under the topic of Resources (Flores and others). Geologic Framework studies provide background information that is the scientific basis for present and future studies of the environment, mineral and energy resources, paleoclimate, and hazards in Alaska. One paper presents the results of sedimentologic and paleontologic comparisons of lower Paleozoic, deep-water-facies rock units in central Alaska (Dumoulin and others). The authors show which of these units are likely to correlate with one another, suggest likely source regions, and provide a structural restoration of units that have been fragmented by large fault motions. A second framework paper provides a map, rock descriptions, and chemical compositions of volcanic rocks in a newly recognized, geologically young volcanic center in the Aleutian volcanic arc (Hildreth and others). A third paper presents an interesting summary of gravity changes that occurred in south-central Alaska during the great earthquake of 1964 and for the following 25 years (Barnes). Gravity changes correlate with land-elevation changes in some cases, but not in others, which means that different processes are responsible for the gravity changes.

Alaska↗
USGS2000

Geologic studies in Alaska by the U.S. Geological Survey, 1998

The 14 papers that follows continue the series of U.S. Geological Survey (USGS) reports on investigations in the geologic sciences in Alaska. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation’s needs for earth-science information in Alaska.

Alaska↗