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At least 325 records · Page 18Linked to original sources
USGS1970

The Alaska earthquake, March 27, 1964: Lessons and conclusions

One of the greatest earthquakes of all time struck south-central Alaska on March 27, 1964. Strong motion lasted longer than for most recorded earthquakes, and more land surface was dislocated, vertically and horizontally, than by any known previous temblor. Never before were so many effects on earth processes and on the works of man available for study by scientists and engineers over so great an area. The seismic vibrations, which directly or indirectly caused most of the damage, were but surface manifestations of a great geologic event-the dislocation of a huge segment of the crust along a deeply buried fault whose nature and even exact location are still subjects for speculation. Not only was the land surface tilted by the great tectonic event beneath it, with resultant seismic sea waves that traversed the entire Pacific, but an enormous mass of land and sea floor moved several tens of feet horizontally toward the Gulf of Alaska. Downslope mass movements of rock, earth, and snow were initiated. Subaqueous slides along lake shores and seacoasts, near-horizontal movements of mobilized soil (“landspreading”), and giant translatory slides in sensitive clay did the most damage and provided the most new knowledge as to the origin, mechanics, and possible means of control or avoidance of such movements. The slopes of most of the deltas that slid in 1964, and that produced destructive local waves, are still as steep or steeper than they were before the earthquake and hence would be unstable or metastable in the event of another great earthquake. Rockslide avalanches provided new evidence that such masses may travel on cushions of compressed air, but a widely held theory that glaciers surge after an earthquake has not been substantiated. Innumerable ground fissures, many of them marked by copious emissions of water, caused much damage in towns and along transportation routes. Vibration also consolidated loose granular materials. In some coastal areas, local subsidence was superimposed on regional tectonic subsidence to heighten the flooding damage. Ground and surface waters were measurably affected by the earthquake, not only in Alaska but throughout the world. Expectably, local geologic conditions largely controlled the extent of structural damage, whether caused directly by seismic vibrations or by secondary effects such as those just described. Intensity was greatest in areas underlain by thick saturated unconsolidated deposits, least on indurated bedrock or permanently frozen ground, and intermediate on coarse well-drained gravel, on morainal deposits, or on moderately indurated sedimentary rocks. Local and even regional geology also controlled the distribution and extent of the earthquake's effects on hydrologic systems. In the conterminous United States, for example, seiches in wells and bodies of surface water were controlled by geologic structures of regional dimension. Devastating as the earthquake was, it had many long-term beneficial effects. Many of these were socioeconomic or engineering in nature; others were of scientific value. Much new and corroborative basic geologic and hydrologic information was accumulated in the course of the earthquake studies, and many new or improved investigative techniques were developed. Chief among these, perhaps, were the recognition that lakes can be used as giant tiltmeters, the refinement of methods for measuring land-level changes by observing displacements of barnacles and other sessile organisms, and the relating of hydrology to seismology by worldwide study of hydroseisms in surface-water bodies and in wells. The geologic and hydrologic lessons learned from studies of the Alaska earthquake also lead directly to better definition of the research needed to further our understanding of earthquakes and of how to avoid or lessen the effects of future ones. Research is needed on the origins and mechanisms of earthquakes, on crustal structure, and on the generation of tsunamis and local waves. Better earthquake-hazard maps, based on improved knowledge of regional geology, fault behavior, and earthquake mechanisms, are needed for the entire country. Their preparation will require the close collaboration of engineers, seismologists, and geologists. Geologic maps of all inhabited places in earthquake-prone parts of the country are also needed by city planners and others, because the direct relationship between local geology and potential earthquake damage is now well understood. Improved and enlarged nets of earthquake-sensing instruments, sited in relation to known geology, are needed, as are many more geodetic and hydrographic measurements. Every large earthquake, wherever located, should be regarded as a full-scale laboratory experiment whose study can give scientific and engineering information unobtainable from any other source. Plans must be made before the event to insure staffing, funding, and coordination of effort for the scientific and engineering study of future earthquakes. Advice of earth scientists and engineers should be used in the decision-making processes involved in reconstruction after any future disastrous earthquake, as was done after the Alaska earthquake. The volume closes with a selected bibliography and a comprehensive index to the entire series of U.S. Geological Survey Professional Papers 541-546. This is the last in a series of six reports that the U.S. Geological Survey published on the results of a comprehensive geologic study that began, as a reconnaissance survey, within 24 hours after the March 27, 1964, Magnitude 9.2 Great Alaska Earthquake and extended, as detailed investigations, through several field seasons. The 1964 Great Alaska earthquake was the largest earthquake in the U.S. since 1700. Professional Paper 546, in 1 part, describes Lessons and Conclusions.

Alaska↗
USGS1982

Specification for procurement of water-level sensing instrumentation, specification number HIF-I-1

This specification is to communicate to instrument manufacturers the U.S. Geological Survey 's requirements. It covers systems for sensing the elevation of the water surface on open channels, rivers, lakes, reservoirs, storm-sewer pipes, and observation wells at Survey data-collection sites. The signal output (mechanical or electrical) must meet the signal input requirements of analog to digital and digital input recorders in use by the Survey. A classification of stage-sensing systems by common characteristics is used to aid Survey people making system selections. These characteristics are (1) system type (contact or noncontact), (2) sensor type and sensing distance, (3) accuracy, (4) range, (5) power requirements, (6) system size and weight, and (7) data output signal. Acceptable system requirements cover system configurations, signal outputs, materials, operation manuals, detailed environmental conditions, calibration procedures, system accuracy, power requirements, installation limitations, maintainability, safety, and workmanship. An outline of the qualification test procedures and failure criteria are also given. The Hydrologic Instrumentation Facility at NSTL Station, Mississippi will test available systems to determine if they meet the specification in this report for inclusion in the Survey 's 'Qualified Products List'. This list will be used for future procurement of water-level sensing systems by the Survey. (USGS)

Open-File Report↗
USGS2014

USGS/EPA collection protocol for bacterial pathogens in soil

This Sample Collection Procedure (SCP) describes the activities and considerations for the collection of bacterial pathogens from representative surface soil samples (0-5 cm). This sampling depth can be reached without the use of a drill rig, direct-push technology, or other mechanized equipment. This procedure can be used in most soil types but is limited to sampling at or near the ground surface. This protocol has components for two different types of sampling applications: (1) typical sampling, when there is no suspicion of contamination (e.g., surveillance or background studies); and (2) in response to known or suspected accidental contamination (e.g., the presence of animal carcasses). This protocol does not cover sampling in response to a suspected bioterrorist or intentional release event. Surface material is removed to the required depth (0-5 cm) and clean trowel or 50 ml sample tube is used to collect the sample. Sample containers are sealed, bagged, and shipped to the laboratory for analysis. Associated documentation, including a Field Data Log and Chain-of-Custody are also included in this document.

Report↗
USGS2012

Summary of oceanographic and water-quality measurements near the Blackwater National Wildlife Refuge, Maryland, 2011

Suspended-sediment transport is a critical element governing the geomorphology of tidal marshes. Marshes rely on both organic material and inorganic sediment deposition to maintain their elevation relative to sea level. In wetlands near the Blackwater National Wildlife Refuge, Maryland, portions of the salt marsh have been subsiding relative to sea level since the early 20th century. Other portions of the marsh have been successful at maintaining elevation. The U.S. Geological Survey performed observational deployments to measure suspended-sediment concentration in the tidal channels in order to understand the magnitude of suspended-sediment concentrations, the sediment-transport mechanisms, and differences between two marsh areas, one that subsided and one that maintained elevation. We deployed optical turbidity sensors and acoustic velocity meters at multiple sites over two periods in 2011. This report presents the time-series of oceanographic data collected during those field studies, including velocity, depth, turbidity, salinity, water temperature, and pH.

Maryl↗
USGS2004

Selenium loading through the Blackfoot River watershed--linking sources to ecosystem

The upper Blackfoot River watershed in southeast Idaho receives drainage from 11 of 16 phosphate mines that have extracted ore from the Phosphoria Formation, three of which are presently active. Toxic effects from selenium (Se), including death of livestock and deformity in aquatic birds, were documented locally in areas where phosphatic shales are exposed ( Piper et al., 2000 ; Presser et al., Chapter 11). Current drainage conditions are leading to Se bioaccumulation at concentrations that pose a risk to fish in the Blackfoot River and its tributaries (Hamilton et al., Chapter 18). A gaging station on the Blackfoot River was re-activated in April 2001 to assess hydrologic conditions and concentration, load, and speciation for Se discharges on a watershed scale. The gaging-station data are considered to represent regional drainage conditions in the upper Blackfoot River water- shed because of its location near the outlet of the watershed and directly upstream of the Blackfoot Reservoir. Watershed discharges for 2001 and 2002 were below minimum hydrologic conditions for the gage as documented by the historical record. Drought emergencies were declared in the area in both 2001 and 2002. Unmonitored diversions for irrigation that routinely take place during the snowmelt season also affected conditions downstream. Annual cycles in Se concentration, load, and selenate (Se 6+ ) reached maxima in the spring during the period of maximum flow at the gaging station. Thirty-seven to 44% of annual flow occurred dur- ing the three-month high-flow season (April through June) in 2001 and 56% of annual flow occurred during that time period in 2002. Extrapolation from historical hydrographs for average and wet years and a limited data set of regional Se concentrations for 2001 and 2002 indicated potential for a 3.6- to 7.4-fold increase in Se loading because of increased seasonal flows in the Blackfoot River watershed. Supplementation data indicate that: (a) the difference between total Se and dissolved Se, as a measure of the contribution of particulate Se, was < 10% except at the peak of con- centration when total Se was 18% more than dissolved Se; (b) selenite (Se 4+ ) represented less than 10% of the dissolved species during all months of 2001; and (c) dissolved Se was approximately a 50:50 mixture of selenate and organic selenide (operationally defined Se 2- ) during summer 2001 (June through August). Ecological risk based on regional Se drainage occurred during both the high- and low-flow seasons. Seventy to 83% of the Se load occurred during the high-flow season. During early May of both years, dissolved-Se concentrations exceeded the criterion for the protection of aquatic life and the ecological threshold of 5 gL 1 Se at which sub- stantive risk occurs. During the majority of the three-month high-flow season, dissolved- Se concentrations exceeded the 2 gL 1 Se concern level for aquatic biota. The Se concentration in suspended material during high flow in 2002 was within the range of marginal risk to aquatic life (2-4 gg 1 Se, dry weight). Selenate was the major species during peak flows, with both selenate and organic selenide being major species during relatively low-flow periods in summer. A change in speciation to reduced Se may indicate elevated biotic productivity during summer months and could result in enhanced Se uptake in food webs. In addition to the magnitude of regional Se release in the Blackfoot River watershed, Se concentrations in individual source drains and waste-rock seeps, and those predicted by experimental column leaching of proposed mining overburden materials, also indicate that drainage options that currently meet existing demands for phosphate mining cause eco- logical risk thresholds to be exceeded. At times, the drinking-water Se standard (50 g L 1 Se) and the criterion for hazardous Se waste (1000 L -1 Se) ( US Department of the Interior, 1998 ; US Environmental Protection Agency, 1987 ) are also exceeded. For water-years 2001 and 2002, seasonal increased input of water in the mining area resulted in increased Se transport, suggesting a mechanism of contamination that involves a significant Se reservoir. Hence, recognition and monitoring of Se loading to the envi- ronment on a mass balance basis (i.e. inputs, fluxes and storage within environmental media, and outputs) are essential to evaluating how to control Se concentrations within environmentally protective ranges ( Presser and Piper, 1998 ). In areas where release of Se to aquatic systems is anticipated as a product of future expansion of phosphate mining, continuous monitoring of flow and development of seasonal Se loading patterns would help to model watersheds in terms of sources, flow periods, and environmental-Se con- centrations that most influence bioavailability. These data, in turn, could be linked to Se- bioaccumulation models specific to food webs and vulnerable species of the impacted areas to accurately project ecological effects. Gaging at this site on the Blackfoot River is planned to continue in order to establish a long-term (>10 year) record of hydrologic conditions.

Idaho↗
USGS1991

Late Laramide thrust-related and evaporite-domed anticlines in the southern Piceance Basin, northeastern Colorado Plateau

New seismic and gravity data across the hydrocarbon-producing Divide Creek and Wolf Creek anticlines in the southern Piceance basin reveal contrasting styles of deformation within two widely separated time frames. Seismic data indicate that prebasin Paleozoic deformation resulted in block faulting of the Precambrian crystalline basement rocks and overlying Cambrian through Middle Pennsylvanian strata. Movement along these block faults throughout much of Pennsylvanian time, during northeast-southwest crustal extension, likely influenced distribution of the Middle Pennsylvanian (Desmoinesian) evaporite-rich facies. Younger rocks, including the thick succession of Cenozoic basin strata, then buried the Paleozoic structures. Tectonic reconfiguration of the basin's eastern margin occurred during late Laramide northeast-southwest compression, when a basement-involved thrust block, whose surface expression is the Grand Hogback monocline, moved into the Piceance basin. A decollement developed in front of the thrust block within the mechanically weak Desmoinesian evaporites and splayed out basinward as small-scale imbricate thrusts in the Upper Cretaceous Mancos Shale. The Divide Creek anticline formed above these splays as thrusting locally overthickened the shale and repeated the sandstone units between it and the evaporites. The Wolf Creek anticline to the east, however, is due to both depositional and tectonic thickening of the evaporite section along the decollement. Gravity data confirm that excess mater al of relatively low density exists beneath the Wolf Creek structure, whereas material of relatively higher density (overthickened shale) is found beneath the Divide Creek anticline. Thrust-related basin margins and intrabasin folds structurally analogous to the Divide Creek and Wolf Creek anticlines may be more common than presently recognized in the Rocky Mountain foreland. One well-documented example is the Pinedale anticline in the northern Green River basin, Wyoming, which, like the Divide Creek anticline, developed above a zone of splay faults from a decollement in front of a large thrust block.

Colorado↗
USGS1974

Appraisal of operating efficiency of recharge basins on Long Island, New York, in 1969

Recharge basins on Long Island are unlined pits of various shapes and sizes excavated in surficial deposits of mainly glacial origin. Of the 2,124 recharge basins on Long Island in 1969, approximately 9 percent (194) contain water 5 or more days after a 1-inch rainfall. Basins on Long Island contain water because (1) they intersect the regional water table or a perched water table, (2) they are excavated in material of low hydraulic conductivity, (3) layers of sediment and debris of low hydraulic conductivity accumulate on the basin floor, or (4) a combination of these factors exists. Data obtained as part of this study show that (1) 22 basins contain water because they intersect the regional water table, (2) a larger percentage of the basins excavated in the Harbor Hill and the Ronkonkoma morainal deposits contain water than basins excavated in the outwash deposits, (3) a larger percentage of the basins that drain industrial and commercial areas contain water than basins that drain highways and residential areas, (4) storm runoff from commercial and industrial areas and highway: generally contains high concentrations of asphalt, grease, oil, tar, and rubber particles, whereas runoff from residential areas mainly contains leaves, grass cuttings, and other plant material, and (5) differences in composition of the soils within the drainage areas of the basins on Long Island apparently are not major factors in causing water retention. Water-containing basins dispose of an undetermined amount of storm runoff primarily by the slow infiltration of water through the bottoms and the sides of the basins. The low average specific conductance of water in most such basins suggests that evaporation does not significantly concentrate the chemical constituents and, therefore, that evaporation is not a major mechanism of water disposal from these basins.

Water Supply Paper↗
USGS1981

Eolian features produced by the December 1977 windstorm, southern San Joaquin Valley, California

High wind velocities during a windstorm in December of 1977 in the southern San Joaquin Valley, California, created eolian features and effects of a magnitude not previously reported in the literature. Three principal mechanisms of sediment movement by wind were studied by examining the size distribution of deposits in telephone poles (saltation and suspension), feeder pens and abandoned buildings (saltation and suspension), and gravel ripples (surface creep). The maximum grain sizes of rocks lodged in telephone poles at heights of 240, 160, and 80 cm are 7 mm X 11 mm X 6 mm, 10 mm X 15 mm X 6 mm, and 20 mm X 23 mm X 5 mm, respectively. In some areas with rocky soils, lag materials formed gravel ripples.

Journal of Geology↗
USGS2001

Vertical profiles of streambed hydraulic conductivity determined using slug tests in central and western Nebraska

Many issues of water-resources management rely on modeling of ground-water/surfacewater interactions, and streambed hydraulic conductivity is a key parameter controlling the water fluxes across the stream/aquifer interface. However, in central and western Nebraska, this parameter is generally undefined. The U.S. Geological Survey, in cooperation with the Nebraska Platte River Cooperative Hydrology Study Group, performed slug tests at 15 stream sites in the Platte, Republican, and Little Blue River watersheds to determine the hydraulic conductivity of streambeds in central and western Nebraska. Slug tests were completed at several discrete depth intervals using pneumatic or mechanical methods, and the water-level response was monitored on site using a pressure transducer and laptop computer. Responses were analyzed using either the Bouwer and Rice or Springer and Gelhar methods. Vertical profiles of hydraulic conductivity with depth were developed and were compared to available information on lithology. The profiles and corresponding lithology showed that different types of streambeds were tested and suggested that some streambeds display a large variability in hydraulic conductivity with depth. In some cases, hydraulic conductivity values associated with nonstreambed materials could be identified from nearby lithologic descriptions. Seven of 15 sites had streambed values that ranged over more than 3 orders of magnitude, and that variability increased significantly when the measurements considered to be from nonstreambed materials were included. Streambed profiles from the Platte and South Platte River sites generally were more homogeneous and of larger hydraulic conductivity than the other sites. No restrictive layers were detected at any of the streambed sites on the main stems or the flood plains of the main stems of their respective watersheds. Alternatively, the profiles characterized by a restrictive streambed layer at some depth below the streambed surface were all from tributary sites out of the main-stem flood plain. These profiles can be used to represent the streambed hydraulic conductivity in central and western Nebraska in various applications, including modeling ground-water/surfacewater interactions.

Nebraska↗
USGS1991

Examination of micrinite concentrates from the Cannel City coal bed of eastern Kentucky: Proposed mechanism of formation

A high volatile B, micrinite-rich bituminous coal from Morgan County, Kentucky, was crushed and screened to −100 mesh, demineralized and subjected to density gradient centrifugation (DGC). In an initial density separation, micrinite concentration was increased from 52 vol% in the demineralized coal to a maximum of 67% in the 1.25–1.26 g/ml density fraction. Micrinite enriched fractions (1.21–1.29 g/ml) were combined to yield a sample containing ∼61% micrinite. This sample was crushed to −200 mesh in an attempt to enhance micrinite liberation then reprocessed by DGC. Reprocessing resulted in a slight increase in purity to 69 vol% in the 1.25–1.28 g/ml density fraction. The original −100 mesh sample was density separated a second time with the material recovered between 1.22 and 1.30 g/ml combined, crushed, screened past 325 mesh and reprocessed by DGC. Micrinite was recovered at a purity ranging up to 73% (1.27–1.28 g/ml) from the −325 mesh sample. A density of 1.26g/ml and H/C atomic ratio of 0.79 was calculated for micrinite in one of the higher purity micrinite fractions. These values are notably different than published fusinite values and are more similar to vitrinite values measured in high volatile-B coals. The results from this study suggest that the partitioning of micrinite to a density near that of vitrinite was governed by the inherent micrinite density and not particle aggregation. Transition of the micrinite precursors through a mobile liquid phase is proposed as an explanation for the discrepancy between chemical properties and reflectance as well as to account for the observed microlithological occurrences of micrinite in this sample.

Kentucky↗
USGS2022

Compression behavior of hydrate-bearing sediments

This work experimentally explores porosity, compressibility, and the ratio of horizontal to vertical effective stress ( K 0 ) in hydrate-bearing sandy silts from Green Canyon Block 955 in the deep-water Gulf of Mexico. The samples have an in situ porosity of 0.38 to 0.40 and a hydrate saturation of more than 80%. The hydrate-bearing sediments are stiffer than the equivalent hydrate-free sediments; the K 0 stress ratio is greater for hydrate-bearing sediments relative to the equivalent hydrate-free sediments. The porosity decreases by 0.01 to 0.02 when the hydrate is dissociated at the in situ effective stress. We interpret that the hydrate in the sediment pores is a viscoelastic material that behaves like a fluid over experimental time scales, yet it cannot escape the sediment skeleton. During compression, the hydrate bears a significant fraction of the applied vertical load and transfers this load laterally, resulting in the apparent increased stiffness and a larger apparent K 0 stress ratio. When dissociation occurs, the load carried by the hydrate is transferred to the sediment skeleton, resulting in further compaction and a decrease in the lateral stress. The viewpoint that the hydrate is a trapped viscous phase provides a mechanism for how stiffness and stress ratio ( K 0 ) are greater when hydrate is present in the porous media. This study provides insight into the initial stress state of hydrate-bearing reservoirs and the geomechanical evolution of these reservoirs during production.

Louisiana↗
USGS2006

Shallow-water pockmark formation in temperate estuaries: A consideration of origins in the western gulf of Maine with special focus on Belfast Bay

A systematic mapping program incorporating more than 5000 km of side scan sonar and seismic reflection tracklines in the western Gulf of Maine has identified more than 70 biogenic natural gas deposits, occupying 311 km 2 in nearshore muddy embayments. Many of these embayments also contain pockmark fields, with some exhibiting geologically active characteristics including the observance of plumes of escaping fluids and sediment. Pockmarks, hemispherically shaped depressions of various size and depths, formed through fluid escape of gas and/or pore water, are sometimes found within or outside gas fields, although many gas fields lack pockmarks altogether. Although the origin of the natural gas remains unclear, if coastal environments at times of lower sea level were similar to the present, numerous lake, wetland, valley fill and estuarine sources of organic-rich material may have formed on the inner shelf. If these deposits survived transgression and remain buried, they are potential gas sources. Intensive mapping of the Belfast Bay pockmark field in 1998 produced the first nearly continuous side scan sonar mosaic of a Gulf of Maine pockmark field with a corresponding 3-dimensional geological model generated from seismic data. Statistical analysis of pockmark geometry, gas deposit loci, and subsurface evidence for gas-enhanced reflectors suggest that gas migration from deeper lateral sources along permeable subsurface strata may be the mechanism for pockmark formation in areas lacking gas-curtain seismic reflections. The coarse-grained transgressive ravinement unconformity between Pleistocene glacial-marine mud and Holocene mud may act as a conduit for distributing methane to the field's margins. ?? 2005 Elsevier B.V. All rights reserved.

Marine Geology↗
USGS1997

Sr-isotopic evidence for leakage of pore water from clay-silt confining units to the Atlantic City 800-foot sand, Atlantic City, New Jersey

The evolution of water quality in confined aquifers in the New Jersey Coastal Plain may be affected by leakage of pore water from the adjacent confining units. We investigated the distribution and sources of solutes, particularly Sr, in pore water mechanically extracted from clay-silt core samples collected from depths of 552–840 ft (168–256 m) in the lower Miocene Kirkwood Formation at Atlantic City, New Jersey (Ocean Drilling Program Leg 150X). The sampled sediments consist of thin clay-silt stringers in the upper part of the Atlantic City 800-ft sand, a major aquifer, and the massive clay-silt units above and below it. The distribution of Sr and the ratio of 87 Sr to 86 Sr in the pore water and adjacent shell material were used to identify the possible sources of, and physical processes that may affect the distribution of, Sr in the pore water. Concentrations of Sr in 14 pore-water samples from the clay-silt unit above the aquifer and the clay-silt interbeds in the upper part of the aquifer ranged from 2.74 to 28.19 µM/L; those in the four pore-water samples from the clay-silt unit below the aquifer ranged from 0.52 to 7.30 µM/L. Concentrations of Sr in the samples varied with depth but correlated strongly with pore-water concentrations of Ca, Mg, Na, and SO4. Cation-exchange processes may be responsible, in part, for the lower concentrations of Sr, Ca, and Mg in pore water from the clay-silt unit below the aquifer than in that above the aquifer. 87 Sr/ 86 Sr values in 11 samples of aragonitic mollusk shells (bearing no visible evidence of recrystallization) collected from depths in the clay-silt unit similar to those from which the pore-water samples were collected ranged from 0.708468 to 0.708713 , and decreased (Sr in the shells was less radiogenic) with depth. This trend is consistent with the decrease in the 87 Sr/ 86 Sr value in seawater through time during the early Miocene. The 87 Sr/ 86 Sr values in 12 pore-water samples from the studied stratigraphic interval ranged from 0.708257 to 0.708527 and also decreased with depth. The Sr-isotope ratios in the pore water were lower than those in the shell material from nearby or adjacent sediments for all samples but one. Because the only known source of Sr with an isotope ratio this low is shell material from sediments deeper than the strata from which the pore-water samples were collected (including pre-Miocene stratigraphic units), the isotope ratio in the pore-water samples from the lower Miocene claysilt units may result from upward movement of pore water into lower Miocene strata through geologic time, which could create the observed difference in Sr isotope ratios between the pore water and shells.

New Jersey↗
USGS1992

Growth of grain contacts in halite by solution-transfer: Implications for diagenesis, lithification, and strength recovery

Lithification of a sediment to form a rock may involve cementation, diagenetic reactions, or compaction under load. In these experiments, convex halite lenses were pressed against fiat halite plates at 50° C in a specially designed microscope stage. A saturated brine surrounded the samples, which were observed during the experiment in transmitted and reflected light. No time-dependent convergence was observed between the two crystals, even at mean normal stresses of up to 14 M Pa at the contact. In all experiments, however, the contact (or neck) between the two crystals grew with time as material dissolved from the surrounding lens surfaces, diffused through the pore fluid, and precipitated at the neck. Neck growth rates did not appear to correlate with the applied load, but did systematically increase as the misorientation between the two crystals decreased. Our analysis of the shapes of fluid inclusions formed along the grain boundary within the neck suggests that the grain boundary energy is about 1.8 times greater than the fluid-solid interfacial energy. Neck growth appears to be driven by the reduction of interfacial energy rather than by mechanical loads. Assuming that the interfacial energy is isotropic, and incorporating some geometric simplifications, two models of neck growth were formulated. The rate-controlling steps in the models were either precipitation or diffusion in the pore fluid. The data fit either model equally well. Both models predict that neck growth rate will be rapid at first but will decrease with time, as was observed. Neck growth will lead to an increase in real area of contact between grains in a granular aggregate even without the introduction of supersaturated solutions and may be important in the induration of sediments and the strengthening of fault gouge.

International Geophysics↗
USGS1990

Enzyme leaching of surficial geochemical samples for detecting hydromorphic trace-element anomalies associated with precious-metal mineralized bedrock buried beneath glacial overburden in northern Minnesota

One objective of the International Falls and Roseau, Minnesota, CUSMAP projects was to develop a means of conducting regional-scale geochemical surveys in areas where bedrock is buried beneath complex glacially derived overburden. Partial analysis of B-horizon soils offered hope for detecting subtle hydromorphic trace-element dispersion patterns. An enzyme-based partial leach selectively removes metals from oxide coatings on the surfaces of soil materials without attacking their matrix. Most trace-element concentrations in the resulting solutions are in the part-per-trillion to low part-per-billion range, necessitating determinations by inductively coupled plasma/mass spectrometry. The resulting data show greater contrasts for many trace elements than with other techniques tested. Spatially, many trace metal anomalies are locally discontinuous, but anomalous trends within larger areas are apparent. In many instances, the source for an anomaly seems to be either basal till or bedrock. Ground water flow is probably the most important mechanism for transporting metals toward the surface, although ionic diffusion, electrochemical gradients, and capillary action may play a role in anomaly dispersal. Sample sites near the Rainy Lake-Seine River fault zone, a regional shear zone, often have anomalous concentrations of a variety of metals, commonly including Zn and/or one or more metals which substitute for Zn in sphalerite (Cd, Ge, Ga, and Sn). Shifts in background concentrations of Bi, Sb, and As show a trend across the area indicating a possible regional zoning of lode-Au mineralization. Soil anomalies of Ag, Co, and Tl parallel basement structures, suggesting areas that may have potential for Cobalt/Thunder Baytype silver viens. An area around Baudette, Minnesota, which is underlain by quartz-chlorite-carbonate-altered shear zones, is anomalous in Ag, As, Bi, Co, Mo, Te, Tl, and W. Anomalies of Ag, As, Bi, Te, and W tend to follow the fault zones, suggesting potential for lode-Au deposits. Soil anomalies of Co, Mo, and Tl appear to follow northwest-striking structures that cross the shear zones, suggesting that Thunder Bay-type mineralization may have overprinted earlier mineralization along the shear zones.

Conference Paper↗
USGS1997

Effect of faulting on ground-water movement in the Death Valley Region, Nevada and California

This study characterizes the hydrogeologic system of the Death Valley region, an area covering approximately 100,000 square kilometers. The study also characterizes the effects of faults on ground-water movement in the Death Valley region by synthesizing crustal stress, fracture mechanics, and structural geologic data. The geologic conditions are typical of the Basin and Range Province; a variety of sedimentary and igneous intrusive and extrusive rocks have been subjected to both compressional and extensional deformation. Faulting and associated fracturing is pervasive and greatly affects ground-water flow patterns. Faults may become preferred conduits or barriers to flow depending on whether they are in relative tension, compression, or shear and other factors such as the degree of dislocations of geologic units caused by faulting, the rock types involved, the fault zone materials, and the depth below the surface. The current crustal stress field was combined with fault orientations to predict potential effects of faults on the regional groundwater flow regime. Numerous examples of faultcontrolled ground-water flow exist within the study area. Hydrologic data provided an independent method for checking some of the assumptions concerning preferential flow paths.

California, Nevada↗
USGS1970

Estimates of the mechanical properties of lunar surface using tracks and secondary impact craters produced by blocks and boulders

Estimates of bearing capacities of lunar surfaces using tracks and secondary impact craters produced by blocks and boulders shown in photographs taken by Lunar Orbiters II and III are the same order of magnitude as those reported by the Surveyor project, but they are generally less. Static analyses of 48 lunar blocks and boulders and their tracks yield friction angles between 10° and 30° and averaging about 17°. These values were computed using: (1) Terzaghi's bearing capacity equations for circular footings, (2) Meyerhof's dimensionless numbers for general shear on level surfaces, (3) a cohesion of 10 3 dynes per cm 2 , (4) a density of 1.35 gm per cm 3 for the near surface materials, (5) a density of 2.7 gm per cm 3 for the block or boulder, (6) spheroidal (triaxial) boulders unless definite shapes can be established, (7) footing radii equal to the half-width of the block or boulder, the half-width of the track, and(or) the half-width of the shadow near the base of the block or boulder. For 115 secondary impact craters and their corresponding blocks, dynamic strengths are estimated using: (1) the product of one-half the mass per unit area of the block and the normal component of velocity squared divided by the crater depth, and (2) the ratio of the kinetic energy of the block and the volume of the secondary crater. Velocities of the blocks are calculated using a ballistics equation and assuming an ejection angle of 45°. Block densities are taken as 2.7 gm per cm 3 . Dynamic strengths of the near surface materials using the first procedure average 25.2 x 10 5 dynes per cm 2 (37 psi); and, for the second procedure, they average 19.2 x 10 5 dynes per cm 2 (28 psi). Comparison between dynamic strengths and expected static strengths, computed for each block using the assumptions above, show that most of the dynamic strengths correspond to the static strengths when the friction angle is 30° and larger. Data on experimental low velocity impacts with natural targets are compared with the lunar data on secondary impacts. Nara's modified Poncelet equation for sand yields an average angle of internal friction near 34° using the appropriate block and soil constants mentioned above. Comparison of coefficients computed using the equations for sand of Clark and McCarty, Mortensen, and Moore for the lunar data with the corresponding constants for terrestrial data indicate the lunar coefficients are generally low. These low values can be brought into better agreement with terrestrial data on sand by increasing the assumed ejection angles to 60° or 70° and considering the effect of the low acceleration of gravity at the lunar surface.

Open-File Report↗
USGS1998

Dispersal of mimetic seeds of three species of Ormosia (Leguminosae)

Seeds with ‘imitation arils’ appear wholly or partially covered by pulp or aril but actually carry no fleshy material. The mimetic seed hypothesis to explain this phenomenon proposes a parasitic relationship in which birds are deceived into dispersing seeds that resemble bird-dispersed fruits, without receiving a nutrient reward. The hard-seed for grit hypothesis proposes a mutualistic relationship in which large, terrestrial birds swallow the exceptionally hard mimetic seeds as grit for grinding the softer seeds on which they feed. They defecate, dispersing the seeds, and abrade the seed surface, enhancing germination. Any fruit mimicry is incidental. Fruiting trees of Ormosia spp. (Leguminosae: Papilionoideae) were observed to ascertain mechanisms of seed dispersal and the role of seemingly mimetic characteristics of the seeds in that dispersal. Seed predation and seed germination were also examined. Ormosia isthamensis and O. macrocalyx (but not O. bopiensis ) deceived arboreally-foraging frugivorous birds into taking their mimetic seeds, although rates of seed dispersal were low. These results are consistent with the mimetic seed hypothesis. On the other hand, the rates of disappearance of seeds from the ground under the Ormosia trees, hardness of the seeds, and enhancement of germination with the abrasion of the seed coat are all consistent with the hard-seed for grit hypothesis.

Journal of Tropical Ecology↗