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USGS1998

Transmissivity and water quality of water-producing zones in the intermediate aquifer system, Sarasota County, Florida

The intermediate aquifer system is an important water source in Sarasota County, Florida, because the quality of water in it is usually better than that in the underlying Upper Floridan aquifer. The intermediate aquifer system consists of a group of up to three water-producing zones separated by less-permeable units that restrict the vertical movement of ground water between zones. The diverse lithology, that makes up the intermediate aquifer system, reflects the variety of depositional environments that occurred during the late Oligocene and Miocene epochs. Slight changes in the depositional environment resulted in aquifer heterogeneity, creating both localized connection between water-producing zones and abrupt culmination of water-producing zones that are not well documented. Aquifer heterogeneity results in vertical and areal variability in hydraulic and water-quality properties. The uppermost water-producing zone is designated producing zone 1 but is not extensively used because of its limited production capability and limited areal extent. The second water-producing zone is designated producing zone 2, and most of the domestic- and irrigation-supply wells in the area are open to this zone. Additionally, producing zone 2 is utilized for public supply in southern coastal areas of Sarasota County. Producing zone 3 is the lowermost and most productive water-producing zone in the intermediate aquifer system. Public-supply well fields serving the cities of Sarasota and Venice, as well as the Plantation and Mabry Carlton Reserve well fields, utilize producing zone 3. Heads within the intermediate aquifer system generally increase with aquifer depth. However, localized head-gradient reversals occur in the study area, coinciding with sites of intense ground-water withdrawals. Heads in producing zones 1, 2, and 3 range from 1 to 23, 0.2 to 34, and 7 to 42 feet above sea level, respectively. Generally, an upward head gradient exists between producing zones 3 and 2. However, an upward head gradient between producing zones 2 and 1 does not consistently occur throughout Sarasota County, probably the result of greater ground-water withdrawals from producing zone 2 than from producing zone 1. The transmissivity of the intermediate aquifer system is spatially variable. Specific-capacity data from selected wells penetrating producing zones 2 and 3, were used to estimate transmissivity. Estimated transmissivity values for producing zones 2 and 3 range from about 100 to 26,000 feet squared per day and from about 1,300 to 6,200 feet squared per day, respectively. Because the capacity of specific water-producing zones is highly variable from site to site, estimating the performance of a specific water-producing zone as a water resource is difficult. Water samples collected during the study were analyzed for major-ion concentrations. Generally, bicarbonate type water from rock interaction occurs in northern Sarasota County; enriched calcium-magnesium-sulfate type water from deeper aquifers occurs in central Sarasota County; and sodium-chloride type water from saltwater mixing occurs in southern Sarasota County. In some areas of northern Sarasota County, the major-ion concentrations in water are lower in producing zone 2 than in producing zone 1. Major-ion concentrations in water are higher in producing zone 3 throughout the study area. A major objective of the study was to evaluate hydraulic and water-quality data to determine distinctions that could be used to characterize a particular producing zone. However, data indicate that both hydraulic and water-quality properties are highly variable within and between zones, and are more related to the degree of connection between and areal extent of water-producing zones than to aquifer depth and distance from the coast.

Florida↗

USGS2006

Phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite

The Campanian Ignimbrite is a > 200 km3 trachyte-phonolite pyroclastic deposit that erupted at 39.3 ?? 0.1 ka within the Campi Flegrei west of Naples, Italy. Here we test the hypothesis that Campanian Ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts (5-10 wt%) of crustal rock (skarns and foid-syenites) during crystallization. Comparison of observed crystal and magma compositions with results of phase equilibria assimilation-fractionation simulations (MELTS) is generally very good. Oxygen fugacity was approximately buffered along QFM+1 (where QFM is the quartz-fayalite-magnetite buffer) during isobaric fractionation at 0.15 GPa (???6 km depth). The parental melt, reconstructed from melt inclusion and host clinopyroxene compositions, is found to be basaltic trachyandesite liquid (51.1 wt% SiO2, 9.3 wt% MgO, 3 wt% H2O). A significant feature of phase equilibria simulations is the existence of a pseudo-invariant temperature, ???883??C, at which the fraction of melt remaining in the system decreases abruptly from ???0.5 to < 0.1. Crystallization at the pseudo-invariant point leads to abrupt changes in the composition, properties (density, dissolved water content), and physical state (viscosity, volume fraction fluid) of melt and magma. A dramatic decrease in melt viscosity (from 1700 Pa s to ???200 Pa s), coupled with a change in the volume fraction of water in magma (from ??? 0.1 to 0.8) and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger. Thermal models suggest a timescale of ??? 200 kyr from the beginning of fractionation until eruption, leading to an apparent rate of evolved magma generation of about 10-3 km3/year. In situ crystallization and crystal settling in density-stratified regions, as well as in convectively mixed, less evolved subjacent magma, operate rapidly enough to match this apparent volumetric rate of evolved magma production. ?? Copyright 2007 Oxford University Press.

Journal of Petrology↗

USGS2015

Uranium in the Wyoming Landscape Conservation Initiative study area, southwestern Wyoming

Wyoming has led the nation as the producer of uranium ore since 1995 and contains the largest reserves of any state. Approximately one third of Wyoming’s total production came from deposits in, or immediately adjacent to, the Wyoming Landscape Conservation Initiative (WLCI) study area in the southwestern corner of the state including all of Carbon, Lincoln, Sublette, Sweetwater, Uinta, and parts of southern Fremont Counties. Conventional open-pit and underground mining methods were employed in the study area until the early 1990s. Since the early 1990s, all uranium mining has been by in-situ recovery (also called in-situ leach). It is estimated that statewide remaining resources of 141,000 tonnes of uranium are about twice the 84,000 tonnes of uranium that the state has already produced. An evaluation of the mineral commodities present in the WLCI study area that may have a role in the development of southwest Wyoming includes uranium. The WLCI study area contains five uranium mineralized areas: Ketchum Buttes, Poison Basin, Shirley Basin, the southern part of Crooks Gap–Green Mountain, and most of Great Divide Basin. Mineralized areas described in the report and outlined on an accompanying map are based on the presence of either contiguous claim blocks, continuous mineralization adjacent to prospective uranium properties, suggestions of mineralization based on site entries in the U.S. Geological Survey’s Mineral Resources Data System (MRDS), or extension of geologic host units or structures. Mineralized areas are not the same as mining districts: the latter have defined administrative boundaries. In the WLCI study area, all uranium areas except Poison Basin and Ketchum Buttes contain roll-front deposits in Eocene (56–34 Ma) sedimentary rocks. Tabular sandstone-hosted uranium deposits are also recognized within the study area.

Wyoming↗

USGS2003

Environmental impacts of petroleum production--Initial results from the Osage-Skiatook Petroleum Environmental Research Sites, Osage County, Oklahoma

Exploration for and production of petroleum have caused major detrimental impacts to soils, surface and ground waters, and the local ecosystems in the United States. These impacts arise primarily from the improper disposal of large volumes of saline water produced with oil and gas, from accidental hydrocarbon and produced water releases, and from abandoned oil wells that were not correctly sealed. It is important to understand the long-term and short-term effects of produced water and hydrocarbon releases from these sites in order to develop risk-based remediation plans. Remediation is particularly needed in aging and depleted fields where land use is changing from petroleum production to residential, agricultural or recreational uses. About 20 scientists from the USGS and other governmental agencies and academia are involved in a multidisciplinary investigation to study the transport, fate, and natural attenuation of inorganic salts, trace metals, organic compounds and radionuclides present in produced water, and their impacts at the Osage-Skiatook Petroleum Environmental Research (OSPER) 'A' and 'B' sites, located on the Osage Reservation in Osage County, Oklahoma. Stakeholders in the project include the Osage Nation, which holds the mineral rights, the Bureau of Indian Affairs with trust responsibility, and the Army Corps of Engineers, which owns the surface rights at these sites and manages adjacent Skiatook Lake. The 4250-hectare Skiatook Lake provides drinking water to local Tulsa suburban communities and a rural water district, and offers recreational fishing and boating opportunities to tens of thousands of visitors each year. Approximately 1.5 and 1.0 hectare of land at the OSPER 'A' (depleted Lester lease) and 'B' (active Branstetter lease) sites, respectively, are affected by salt scarring, tree kills, soil salinization and brine and petroleum contamination due to the leakage of produced water and associated hydrocarbons from brine pits and accidental releases from active and inactive pipes and tank batteries. The leases are typical of many depleted and aging petroleum fields in Osage County, which ranks among the top oil and gas producing counties in Oklahoma with about 39,000 wells. Oil and gas production has occurred in Osage county for over one hundred years, but current production is mainly from stripper wells (averaging ~2.8 bbl/d oil and >30 bbl/d brine) that are shallow, mostly 300-700 m in depth, and produce from several sandstones of Pennsylvanian age. Results to date show that the produced water source is a Na-Ca-Cl brine (~150,000 mg/L total dissolved solids), with relatively high concentrations of Mg, Sr, and NH4, but low SO4 and H2S. With the exception of Fe and Mn, the concentrations of trace metals are low. Results also show that some and, eventually, the bulk, of inorganic salts and some dissolved organic species in the released brine from both sites will reach Skiatook Lake. Results at the 'A' site show that the salts have essentially been removed from the sandy soil which formed in a surficial layer of eolian sand, but degraded and weathered oil persists on the surface of old oil and brine pits, close to sites of old tanks, on old channels that carried oil from tanks to the oil pits and other impacted areas. Results also show a plume of high salinity water (5,000-30,600 mg/L TDS) is present at intermediate depths that extend from below the old oil and brine pits to Skiatook Lake. No liquid petroleum was found in the contaminated groundwater, but soluble petroleum byproducts, including organic acid anions and other volatile organic compounds (VOCs) are present. Results to date clearly show that significant amounts of salts from produced-water releases and petroleum hydrocarbons still remain in the soils and rocks of the impacted area after more than 60 years of natural attenuation.

Oklahoma↗

USGS1987

Microbial infections in a declining wild turkey population in Texas

A survey was conducted at 5 locations in Texas for avian pathogens that might adversely affect wild turkey ( Meleagris gallopavo ) productivity and survival. At 1 site, the Rob and Bessie Welder Wildlife Refuge (WWR), turkeys have declined precipitously in recent years. During the winters of 1983-85, 442 wild turkeys were caught with cannon and drop nets, 161 of these on WWR. Blood samples were drawn for serologic evaluation, and cloacal and tracheal swabs were collected for isolation attempts. Salmonella spp. bacteria, Newcastle disease virus (NDV), and avian influenza virus (AIV) were not detected in any samples tested. Serologic tests for antibodies to NDV and AIV also were negative. Many mycoplasma isolates were recovered from turkeys from every location. Characterization of these isolates indicated that several species were present. None were species typically associated with mycoplasmosis in domestic turkeys, such as Mycoplasma gallisepticum (MG), M. meleagridis (MM), or M. synoviae (MS), although antibodies to these pathogens were detected in turkeys at every location sampled. There was no evidence to link any of these disease causing agents to the decline observed in the population of wild turkeys on the WWR.

Texas↗

USGS1965

Bauxite and Kaolin Deposits of the Irwinton district, Georgia

The Irwinton district is in the central part of Georgia at the inner margin of the Coastal Plain province. The oldest rocks exposed in the district are crystalline rocks of the Piedmont province. They are unconformably overlain by nonmarine sedimentary strata of Late Cretaceous age, including gravel, micaceous sand, and lenses of kaolin. Bauxite has been found in a few of the kaolin lenses near the top of the sequence of these strata. During a long period prior to deposition of the over- lying marine beds of the Claiborne and Jackson Groups (middle and upper Eocene), the Upper Cretaceous strata were subjected to subaerial erosion. The bauxite deposits are considered to have formed during this period. They range in thickness from a few inches to more than 10 feet and occupy areas ranging from a few square feet to more than 5 acres. Most of the known bauxite deposits lie along the valleys of Commissioners Creek and Big Sandy Creek in Wilkinson County. The kaolin lenses are much larger than the bauxite deposits; some of the lenses underlie more than 200 acres and are more than 20 feet thick. Bauxite was discovered in the district in 1907 and was mined from 1910 to 1928. A few additional carloads of ore were shipped in 1941 and 1942, but no ore has been mined since that time. Reserves of high-grade bauxite are very small. Reserves of all grades of bauxite plus bauxitic clay may be about 400,000 long tons. The Irwinton district is the principal source of high-grade kaolin in the United States. The presence of kaolin here has been known since early colo- nial time, and it has been mined continuously since 1897. Production in 1959 was 1,940,279 short tons. The reserves of kaolin are very large but have never been adequately measured. Reserves of first and second grade kaolin may be 67 to 84 million short tons. Kaolin of lower grade is present in larger quantity.

Bulletin↗

USGS2024

California State Waters Map Series—Benthic habitat characterization in the region offshore Humboldt Bay, California

Coastal and Marine Ecological Classification Standard (CMECS) geoform, substrate, and biotic component geographic information system (GIS) products were developed for the California State Waters of northern California in the region offshore of Humboldt Bay. The study was motivated by interest in development of offshore wind-energy capacity and infrastructure in Federal waters offshore. This project, carried out by the U.S. Geological Survey (USGS), resulted in four data releases for individual map blocks that are part of the “California State Waters Map Series”: (1) Offshore of Arcata, (2) Offshore of Eureka, (3) Offshore of the Eel River, and (4) Offshore of Cape Mendocino. The study area consists of 436 square kilometers of multibeam echo sounder (MBES) data acquired by Fugro Pelagos, Inc., in 2007. Towed camera-sled video was acquired in 2009 and 2010 to supervise the classification of the MBES data into habitats, and single channel sparker data were collected to calculate sediment thickness above the transgressive unconformity. Using video observations of habitat as ground truth, derivatives of the MBES data were classified into 3 seafloor character types (hard-rugose, hard-flat, and soft-flat), 26 induration-slope-depth groups, and 15 geoforms. The study area substrate is predominantly soft-flat sediment (mud and fine sand) covering 73.6 percent of the area. Hard-flat substrate areas, predominantly coarse sediment in scour depressions, cover 5.4 percent of the study area. The hard-rugose substrate areas are primarily outcrops of layered sedimentary bedrock and constitute 20.9 percent of the study area. Fifteen geoforms were identified in the analysis. The predominant geoforms mirror the seafloor character results, shelf geoforms, rock outcrop geoforms, and scour depression geoforms. Rock and scour areas are restricted to the southern portion of the study area off Cape Mendocino where uplift has exposed bedrock. On the flat shelf area post-transgressive sediment varies in thickness from 1.7 meters (m) nearshore to 28.1 m offshore.

California↗

USGS1961

Geology and mineral deposits of the Carlile quadrangle, Crook County, Wyoming

The Carlile quadrangle-is along the northwestern flank of the Black Hills uplift in Crook County, Wyo. The area-is primarily one of canyons and divides that are a result of downcutting by the Belle Fourche River and its tributaries through an alternating succession of sandstone, siltstone, and mudstone or shale beds. The present topography is also influenced by the regional structure, as reflected by the beds that dip gently westward and by the local structural features such as anticlines, domes, synclines, basins, and terraces, which are superimposed upon the regional setting. Rocks exposed include shale and thin limestone and sandstone beds belonging to the Redwater shale member of the Sundance formation and to the Morrison formation, both of Late Jurassic age; sandstone, siltstone, and mudstone of the Lakota and Fall River formations of Early Cretaceous age; and shale and sandstone of the Skull Creek shale, Newcastle sandstone, and Mowry shale, also of Early Cretaceous age. In the southwestern part of the quadrangle rocks of the Upper Cretaceous series are exposed. These include the Belle Fourche shale, Greenhorn formation, and Carlile shale. Gravel terraces, landslide debris, and stream alluvium comprise the surficial deposits. The Lakota and Fall River formations, which make up the Iriyan Kara group, contain uranium deposits locally in the northern Black Hills. These formations were informally subdivided in order to show clearly the vertical and lateral distribution of the sandstone, siltstone, and mudstone facies within them. The Lakota was subdivided into a sandstone unit and an overlying mudstone unit; the Fall River was subdivided, in ascending order, into a siltstone unit, a mudstone unit, a sandstone unit, and an upper unit. The lithologic character of the Lakota changes abruptly locally, and the units are quite inconsistent with respect to composition, thickness, and extent. This is in contrast to a notable consistency in the lithologic character and thickness among all the Fall River units, with the exception of the upper unit. Petrographic studies on selected samples of units from both formations show differences in composition between Lakota and Fall River rocks. The Carlile quadrangle lies immediately east of the monocline that marks the outer limit of the Black Hills uplift, and the rocks in this area have a regional dip of less than 2° outward from the center of the uplift. Superimposed upon the regional uplift are many subordinate structural features anticlines, synclines, domes, basins, and terraces which locally modify the regional features. The most pronounced of these subordinate structural features are the doubly-plunging Pine Ridge, Oil Butte, and Dakota Divide anticlines, and the Eggie Creek syncline. Stress throughout the area was relieved almost entirely through folding; only a few small nearly vertical normal faults were found within the quadrangle. Uranium has been mined from the Carlile deposit, owned by the Homestake Mining Co. The ore minerals, carnotite and tyuyamnuite occur in a sandstone lens that is enclosed within relatively impermeable clayey beds in the mudstone unit of the Lakota formation. The ore also includes unidentified black vanadium minerals and possibly coffinite. Uranium minerals are more abundant in and adjacent to thicker carbonaceous and silty seams in the sandstone lens. A mixture of fine-grained calcium carbonate and calcium sulfate fills the interstices between detrital quartz grains in mineralized sandstone. Selenium and arsenic are more abundant in samples that are high in uranium. Drilling on Thorn Divide about 1 mile west of the Carlile mine has roughly outlined concentrations of a sooty black uranium mineral associated with pyrite In two stratigraphic intervals of the Lakota formation. One is in the same sandstone lens that contains the ore at the Carlile mine; the other is in conglomeratic sandstone near the base of the Lakota. These deposits are relatively deep, and no mining has been attempted. The mineralogy of the Carlile deposits and the lithologic features of the sandstone host rock suggest that uranium and vanadium were transported in the high-valent state by carbonate or sulfate solutions, were extracted from solution by organic material, and were reduced to low-valent states to form an original assemblage of oxides and silicates. These primary minerals were oxidized in place, and the present carnotite-tyuyamunite assemblage was formed. In general, radioactivity analyses correspond fairly closely with chemical analyses of uranium, thus it is believed that only minor solution and migration of uranium has occurred since the present suite of oxidized minerals was formed. The factors responsible for ore localization are not clear, but probably a combination of three lithologic and structural elements contributed to provide a favorable environment for precipitating uranium from aqueous solutions: abundant carbonaceous material or pyrite in a thin, permeable sandstone enclosed within relatively thick impermeable clays; local structural basins; and a regional structural setting involving a broad syncline between two anticlines. The structural features controlled the regional flow of ground water and the lithologic features controlled the local rate of flow and provided the proper chemical environment for uranium deposition. Bentonite has been mined from an opencut in the Mowry shale in the southwest part of the quadrangle. A bentonite bed in the Newcastle sandstone also seems to be of minable thickness and quality. Exploration for petroleum has been unsuccessful within the quadrangle; however, some wells that yielded oil were recently drilled on small anticlines to the west and southeast. It is possible that similar structural features in the Carlile area, that were previously overlooked, may be equally productive.

Wyoming↗

USGS2001

Environmental quality and preservation; reefs, corals, and carbonate sands; guides to reef-ecosystem health and environment

Introduction In recent years, the health of the entire coral reef ecosystem that lines the outer shelf off the Florida Keys has declined markedly. In particular, loss of those coral species that are the building blocks of solid reef framework has significant negative implications for economic vitality of the region. What are the reasons for this decline? Is it due to natural change, or are human activities (recreational diving, ship groundings, farmland runoff, nutrient influx, air-borne contaminants, groundwater pollutants) a contributing factor and if so, to what extent? At risk of loss are biologic resources of the reefs, including habitats for endangered species in shoreline mangroves, productive marine and wetland nurseries, and economic fisheries. A healthy reef ecosystem builds a protective offshore barrier to catastrophic wave action and storm surges generated by tropical storms and hurricanes. In turn, a healthy reef protects the homes, marinas, and infrastructure on the Florida Keys that have been designed to capture a lucrative tourism industry. A healthy reef ecosystem also protects inland agricultural and livestock areas of South Florida whose produce and meat feed much of the United States and other parts of the world. In cooperation with the National Oceanic and Atmospheric Administration's (NOAA) National Marine Sanctuary Program, the U.S. Geological Survey (USGS) continues longterm investigations of factors that may affect Florida's reefs. One of the first steps in distinguishing between natural change and the effects of human activities, however, is to determine how coral reefs have responded to past environmental change, before the advent of man. By so doing, accurate scientific information becomes available for Marine Sanctuary management to understand natural change and thus to assess and regulate potential human impact better. The USGS studies described here evaluate the distribution (location) and historic vitality (thickness) of Holocene reefs in South Florida, relative to type of underlying bedrock morphology, and their varied natural response to rising sea level. These studies also assess movement and accumulation of sands, relative to direction of prevailing energy, and origin of the component sand grains. Geophysical data collected with highresolution sound-wave instruments that provide pictures of the sediment and bedrock are used to interpret sediment thickness. Reef thickness is determined by collecting limestone rock cores by drilling. Drill cores through reefs are used to identify the coral species that built them and to determine how reefs reacted to rising sea level. These data are supplemented by using isotope-dating techniques to derive the carbon-14 (C14) age of the corals and mangrove peat in the cores. Mangrove peat forms in very shallow water and at the shoreline but is found today buried beneath offshore reefs.

Open-File Report↗

USGS2013

Nickel-cobalt laterites: A deposit model

Nickel-cobalt (Ni-Co) laterite deposits are supergene enrichments of Ni±Co that form from intense chemical and mechanical weathering of ultramafic parent rocks. These regolith deposits typically form within 26 degrees of the equator, although there are a few exceptions. They form in active continental margins and stable cratonic settings. It takes as little as one million years for a laterite profile to develop. Three subtypes of Ni-Co laterite deposits are classified according to the dominant Ni-bearing mineralogy, which include hydrous magnesium (Mg)-silicate, smectite, and oxide. These minerals form in weathering horizons that begin with the unweathered protolith at the base, saprolite next, a smectite transition zone only in profiles where drainage is very poor, followed by limonite, and then capped with ferricrete at the top. The saprolite contains Ni-rich hydrous Mg-silicates, the Ni-rich clays occur in the transition horizon, and Ni-rich goethite occurs in the limonite. Although these subtypes of deposits are the more widely used terms for classification of Ni-Co laterite deposits, most deposits have economic concentrations of Ni in more than one horizon. Because of their complex mineralogy and heterogeneous concentrations, mining of these metallurgically complex deposits can be challenging. Deposits range in size from 2.5 to about 400 million tonnes, with Ni and Co grades of 0.66–2.4 percent (median 1.3) and 0.01–0.15 percent (median 0.08), respectively. Modern techniques of ore delineation and mineralogical identification are being developed to aid in streamlining the Ni-Co laterite mining process, and low-temperature and low-pressure ore processing techniques are being tested that will treat the entire weathered profile. There is evidence that the production of Ni and Co from laterites is more energy intensive than that of sulfide ores, reflecting the environmental impact of producing a Ni-Co laterite deposit. Tailings may include high levels of magnesium, sulfate, and manganese and have the potential to be physically unstable.

Scientific Investigations Report↗

USGS2012

Lahar hazard zones for eruption-generated lahars in the Lassen Volcanic Center, California

Lahar deposits are found in drainages that head on or near Lassen Peak in northern California, demonstrating that these valleys are susceptible to future lahars. In general, lahars are uncommon in the Lassen region. Lassen Peak's lack of large perennial snowfields and glaciers limits its potential for lahar development, with the winter snowpack being the largest source of water for lahar generation. The most extensive lahar deposits are related to the May 1915 eruption of Lassen Peak, and evidence for pre-1915 lahars is sparse and spatially limited. The May 1915 eruption of Lassen Peak was a small-volume eruption that generated a snow and hot-rock avalanche, a pyroclastic flow, and two large and four smaller lahars. The two large lahars were generated on May 19 and 22 and inundated sections of Lost and Hat Creeks. We use 80 years of snow depth measurements from Lassen Peak to calculate average and maximum liquid water depths, 2.02 meters (m) and 3.90 m respectively, for the month of May as estimates of the 1915 lahars. These depths are multiplied by the areal extents of the eruptive deposits to calculate a water volume range, 7.05-13.6x10 6 cubic meters (m 3 ). We assume the lahars were a 50/50 mix of water and sediment and double the water volumes to provide an estimate of the 1915 lahars, 13.2-19.8x10 6 m 3 . We use a representative volume of 15x106 m 3 in the software program LAHARZ to calculate cross-sectional and planimetric areas for the 1915 lahars. The resultant lahar inundation zone reasonably portrays both of the May 1915 lahars. We use this same technique to calculate the potential for future lahars in basins that head on or near Lassen Peak. LAHARZ assumes that the total lahar volume does not change after leaving the potential energy, H/L , cone (the height of the edifice, H , down to the approximate break in slope at its base, L ); therefore, all water available to initiate a lahar is contained inside this cone. Because snow is the primary source of water for lahar generation, we assume that the maximum historical water equivalent, 3.90 m, covers the entire basin area inside the H/L cone. The product of planimetric area of each basin inside the H/L and the maximum historical water equivalent yields the maximum water volume available to generate a lahar. We then double the water volumes to approximate maximum lahar volumes. The maximum lahar volumes and an understanding of the statistical uncertainties inherent to the LAHARZ calculations guided our selection of six hypothetical volumes, 1, 3, 10, 30, 60, and 90x10 6 m 3 , to delineate concentric lahar inundation zones. The lahar inundation zones extend, in general, tens of kilometers away from Lassen Peak. The small, more-frequent lahar inundation zones (1 and 3x10 6 m 3 ) are, on average, 10 km long. The exceptions are the zones in Warner Creek and Mill Creek, which extend much further. All but one of the small, more-frequent lahar inundation zones reach outside of the Lassen Volcanic National Park boundary, and the zone in Mill Creek extends well past the park boundary. All of the medium, moderately frequent lahar inundation zones (10 and 30x10 6 m 3 ) extend past the park boundary and could potentially impact the communities of Viola and Old Station and State Highways 36 and 44, both north and west of Lassen Peak. The approximately 27-km-long on average, large, less-frequent lahar inundation zones (60 and 90x10 6 m 3 ) represent worst-case lahar scenarios that are unlikely to occur. Flood hazards continue downstream from the toes of the lahars, potentially affecting communities in the Sacramento River Valley.

California↗

USGS2010

Groundwater availability in the Atlantic Coastal Plain of North and South Carolina

The Atlantic Coastal Plain aquifers and confining units of North and South Carolina are composed of crystalline carbonate rocks, sand, clay, silt, and gravel and contain large volumes of high-quality groundwater. The aquifers have a long history of use dating back to the earliest days of European settlement in the late 1600s. Although extensive areas of some of the aquifers have or currently (2009) are areas of groundwater level declines from large-scale, concentrated pumping centers, large areas of the Atlantic Coastal Plain contain substantial quantities of high-quality groundwater that currently (2009) are unused. Groundwater use from the Atlantic Coastal Plain aquifers in North Carolina and South Carolina has increased during the past 60 years as the population has increased along with demands for municipal, industrial, and agricultural water needs. While North Carolina and South Carolina work to increase development of water supplies in response to the rapid growth in these coastal populations, both States recognize that they are facing a number of unanswered questions regarding availability of groundwater supplies and the best methods to manage these important supplies. An in-depth assessment of groundwater availability of the Atlantic Coastal Plain aquifers of North and South Carolina has been completed by the U.S. Geological Survey Groundwater Resources Program. This assessment includes (1) a determination of the present status of the Atlantic Coastal Plain groundwater resources; (2) an explanation for how these resources have changed over time; and (3) development of tools to assess the system's response to stresses from potential future climate variability. Results from numerous previous investigations of the Atlantic Coastal Plain by Federal and State agencies have been incorporated into this effort. The primary products of this effort are (1) comprehensive hydrologic datasets such as groundwater levels, groundwater use, and aquifer properties; (2) a revised hydrogeologic framework; (3) simulated water budgets of the overall study area along with several subareas; and (4) construction and calibration of a numerical modeling tool that is used to forecast the potential effects of climate change on groundwater levels.

North Carolina, South Carolina↗

USGS1971

Petrologic and geophysical nature of serpentinites

Mineralogically, serpentinites consist predominantly of lizardite, clinochrysotile, and antigorite. Recent work has shown that these minerals are not polymorphs. Chrysotile is the only mineral recognized as a synthetic product in experimental studies of the system MgO-SiO 2 -H 2 O. Antigorite seems to be stable at higher temperatures than lizardite or chrysotile. The density of individual serpentine species is dependent on their morphology; the low-density serpentinites (<2.55g/cc) consist predominantly of clino-chrysotile. Seismic velocities and magnetic susceptibilities of serpentinites are related to the degree of serpentinization. The transition of massive serpentinites from ductile to brittle behavior in laboratory experiments at high confining pressures and temperatures above 300°C has been related to dehydration which may provide a mechanism for developing deep-focus earthquakes along Benioff zones. Serpentinite is formed by direct hydration of ultramafic protolith in the crust. The most common ultramafic protoliths are harzburgite, dunite, and Iherzolite. The assemblage generally developed from these is lizardite + chrysotile + brucite + magnetite. In areas of high-grade metamorphism, antigorite is the predominant serpentine mineral. The common, large, alpine-type serpentinized ultramafic masses contain brucite and have MgO/SiO 2 ratios similar to those of their protolith, resulting in volume increase during serpentinization. Metamorphic serpentinites and some highly sheared alpine-type serpentinites have lower MgO/SiO 2 ratios than their protolith, lack brucite, and appear t o have been formed by volume-for-volume replacement with concomitant loss of magnesium or addition of silica. Many large, young masses of peridotite appear to be slabs of oceanic mantle over-thrust onto continental edges. Subsequent sedimentation, serpentinization, and tectonism have greatly modified these original slabs so that their recognition in older orogenic zones is equivocal. The concept of the tectonic evolution of ultramafic rocks from oceanic crust-mantle slabs invading continental margins and being incrementally serpentinized and moved by later tectonic events provides a working hypothesis that allows a better explanation of the many peculiar and varied occurrences of serpentinite. The evidence does not support Hess' suggestion that the third layer of the oceanic crust consists of partly serpentinized mantle peridotite.

Bulletin of the Geological Society of America↗

USGS2001

Sulfur and lead isotope geochemistry of hypogene mineralization at the Barite Hill Gold Deposit, Carolina Slate Belt, southeastern United States: A window into and through regional metamorphism

The Barite Hill gold deposit, at the southwestern end of the Carolina slate belt in the southeastern United States, is one of four gold deposits in the region that have a combined yield of 110 metric tons of gold over the past 10 years. At Barite Hill, production has dominantly come from oxidized ores. Sulfur isotope data from hypogene portions of the Barite Hill gold deposit vary systematically with pyrite–barite associations and provide insights into both the pre-metamorphic Late Proterozoic hydrothermal and the Paleozoic regional metamorphic histories of the deposit. The δ 34 S values of massive barite cluster tightly between 25.0 and 28.0&permil;, which closely match the published values for Late Proterozoic seawater and thus support a seafloor hydrothermal origin. The δ 34 S values of massive sulfide range from 1.0 to 5.3&permil; and fall within the range of values observed for modern and ancient seafloor hydrothermal sulfide deposits. In contrast, δ 34 S values for finer-grained, intergrown pyrite (5.1–6.8&permil;) and barite (21.0–23.9&permil;) are higher and lower than their massive counterparts, respectively. Calculated sulfur isotope temperatures for the latter barite–pyrite pairs (Δ=15.9–17.1&permil;) range from 332–355 °C and probably reflect post-depositional equilibration at greenschist-facies regional metamorphic conditions. Thus, pyrite and barite occurring separately from one another provide pre-metamorphic information about the hydrothermal origin of the deposit, whereas pyrite and barite occurring together equilibrated to record the metamorphic conditions. Preliminary fluid inclusion data from sphalerite are consistent with a modified seawater source for the mineralizing fluids, but data from quartz and barite may reflect later metamorphic and (or) more recent meteoric water input. Lead isotope values from pyrites range for 206 Pb/ 204 Pb from 18.005–18.294, for 207 Pb/ 204 Pb from 15.567–15.645, and for 208 Pb/ 204 Pb from 37.555–38.015. The data indicate derivation of the ore leads from the country rocks, which themselves show evidence for contributions from relatively unradiogenic, mantle-like lead, and more evolved or crustal lead. Geological relationships, and stable and radiogenic isotopic data, suggest that the Barite Hill gold deposit formed on the Late Proterozoic seafloor through exhalative hydrothermal processes similar to those that were responsible for the massive sulfide deposits of the Kuroko district, Japan. On the basis of similarities with other gold-rich massive sulfide deposits and modern seafloor hydrothermal systems, the gold at Barite Hill was probably introduced as an integral part of the formation of the massive sulfide deposit.

Georgia, North Carolina, South Carolina, Virginia↗

USGS1987

The crustal structure of the axis of the Great Valley, California, from seismic refraction measurements

In 1982 the U.S. Geological Survey collected six seismic refraction profiles in the Great Valley of California: three axial profiles with a maximum shot-to-receiver offset of 160 km, and three shorter profiles perpendicular to the valley axis. This paper presents the results of two-dimensional raytracing and synthetic seismogram modeling of the central axial profile. The crust of the central Great Valley is laterally heterogeneous along its axis, but generally consists of a sedimentary section overlying distinct upper, middle, and lower crustal units. The sedimentary rocks are 3-5 km thick along the profile, with velocities increasing with depth from 1.6 to 4.0 km/s. The basement (upper crust) consists of four units: 1. (1) a 1.0-1.5 km thick layer of velocity 5.4-5.8 km/s, 2. (2) a 3-4 km thick layer of velocity 6.0-6.3 km/s, 3. (3) a 1.5-3.0 km thick layer of velocity 6.5-6.6 km/s, and 4. (4) a laterally discontinuous, 1.5 km thick layer of velocity 6.8-7.0 km/s. The mid-crust lies at 11-14 km depth, is 5-8 km thick, and has a velocity of 6.6-6.7 km/s. On the northwest side of our profile the mid-crust is a low-velocity zone beneath the 6.8-7.0 km/s lid. The lower crust lies at 16-19 km depth, is 7-13 km thick, and has a velocity of 6.9-7.2 km/s. Crustal thickness increases from 26 to 29 km from NW to SE in the model. Although an unequivocal determination of crustal composition is not possible from P-wave velocities alone, our model has several geological and tectonic implications. We interpret the upper 7 km of basement on the northwest side of the profile as an ophiolitic fragment, since its thickness and velocity structure are consistent with that of oceanic crust. This fragment, which is not present 10-15 km to the west of the refraction profile, is probably at least partially responsible for the Great Valley gravity and magnetic anomalies, whose peaks lie about 10 km east of our profile. The middle and lower crust are probably gabbroic and the product of magmatic or tectonic underplating, or both. The crustal structure of the Great Valley is dissimilar to that of the adjacent Diablo Range, suggesting the existence of a fault or suture zone throughout the crust between these provinces.

California↗

USGS2014

Growth and degradation of Hawaiian volcanoes

The 19 known shield volcanoes of the main Hawaiian Islands—15 now emergent, 3 submerged, and 1 newly born and still submarine—lie at the southeast end of a long-lived hot spot chain. As the Pacific Plate of the Earth’s lithosphere moves slowly northwestward over the Hawaiian hot spot, volcanoes are successively born above it, evolve as they drift away from it, and eventually die and subside beneath the ocean surface. The massive outpouring of lava flows from Hawaiian volcanoes weighs upon the oceanic crust, depressing it by as much as 5 km along an axial Hawaiian Moat. The periphery of subsidence is marked by the surrounding Hawaiian Arch. Subsidence is ongoing throughout almost all of a volcano’s life. During its active life, an idealized Hawaiian volcano passes through four eruptive stages: preshield, shield, postshield, and rejuvenated. Though imperfectly named, these stages match our understanding of the growth history and compositional variation of the Hawaiian volcanoes; the stages reflect variations in the amount and rate of heat supplied to the lithosphere as it overrides the hot spot. Principal growth occurs in the first 1–2 million years as each volcano rises from the sea floor or submarine flank of an adjacent volcano. Volcanic extinction ensues as a volcano moves away from the hot spot. Eruptive-stage boundaries are drawn somewhat arbitrarily because of their transitional nature. Preshield-stage lava is alkalic as a consequence of a nascent magma-transport system and less extensive melting at the periphery of the mantle plume fed by the hot spot. The shield stage is the most productive volcanically, and each Hawaiian volcano erupts an estimated 80–95 percent of its ultimate volume in tholeiitic lavas during this stage. Shield-stage volcanism marks the time when a volcano is near or above the hot spot and its magma supply system is robust. This most active stage may also be the peak time when giant landslides modify the flanks of the volcanoes, although such processes begin earlier and extend later in the life of the volcanoes. Late-shield strata extend the silica range as alkali basalt and even hawaiite lava flows are sparsely interlayered with tholeiite at some volcanoes. Rare are more highly fractionated shield-stage lava flows, which may reach 68 weight percent SiO 2 . Intervolcano compositional differences result mainly from variations in the part of the mantle plume sampled by magmatism and the distribution of magma sources within it. Volcanism wanes gradually as Hawaiian volcanoes move away from the hot spot, passing from the shield stage into the postshield stage. Shallow magma reservoirs (1–7-km depth) of the shield-stage volcanoes cannot be sustained as magma supply lessens, but smaller reservoirs at 20–30-km depth persist. The rate of extrusion diminishes by a factor of 10 late in the shield stage, and the composition of erupted lava becomes more alkalic—albeit erratically—as the degree of melting diminishes. The variation makes this transition, from late shield to postshield, difficult to define rigorously. Of the volcanoes old enough to have seen this transition, eight have postshield strata sufficiently distinct and widespread to map separately. Only two, Ko‘olau and Lāna‘i, lack rocks of postshield composition. Five Hawaiian volcanoes have seen rejuvenated-stage volcanism following quiescent periods that ranged from 2.0 to less than 0.5 million years. The rejuvenated stage can be brief—only one or two eruptive episodes—or notably durable. That on Ni‘ihau lasted from 2.2 to 0.4 million years ago; on Kaua‘i, the stage has been ongoing since 3.5 million years ago. As transitions go, the rejuvenated stage may be thought of as the long tail of alkalic volcanism that begins in late-shield time and persists through the postshield (+rejuvenated-stage) era. Because successive Hawaiian volcanoes erupt over long and overlapping spans of time, there is a wide range in the age of volcanism along the island chain, even though the age of Hawaiian shields is progressively younger to the southeast. For example, almost every island from Ni‘ihau to Hawai‘i had an eruption in the time between 0.3 and 0.4 million years ago, even though only the Island of Hawai‘i had active volcanoes in their shield stage during that time. Once they have formed, Hawaiian volcanoes become subject to a spectrum of processes of degradation. Primary among these are subaerial erosion, landslides, and subsidence. The islands, especially those that grow high above sea level, experience mean annual precipitation that locally exceeds 9 m, leading to rapid erosion that can carve deep canyons in less than 1 million years. Hawaiian volcanoes have also been modified by giant landslides. Seventeen discrete slides that formed in the past 5 m.y. have been identified around the main Hawaiian Islands, and fully 70 are known along the Hawaiian Ridge between Midway Islands and the Island of Hawai‘i. These giant landslides displace large amounts of seawater to generate catastrophic giant waves (megatsunami). The geologic evidence for megatsunami in the Hawaiian Islands includes chaotic coral and lava-clast breccia preserved as high as 155 m above sea level on Lāna‘i and Moloka‘i. Large Hawaiian volcanoes can persist as islands through the rapid subsidence by building upward rapidly enough. But in the long run, subsidence, coupled with surface erosion, erases any volcanic remnant above sea level in about 15 m.y. One consequence of subsidence, in concert with eustatic changes in sea level, is the drowning of coral reefs that drape the submarine flanks of the actively subsiding volcanoes. At least six reefs northwest of the Island of Hawai‘i form a stairstep configuration, the oldest being deepest.

Hawaii↗

USGS2022

Geochemical studies of the Green River Formation in the Piceance Basin, Colorado: I. Major, minor, and trace elements

The Eocene Green River Formation contains the largest oil shale deposits in the world and is a welldocumented example of a lacustrine depositional system. In addition, mineral resources associated with oil shale in the Piceance Basin nahcolite [NaHCO3] and dawsonite [NaAl(CO3)(OH)2)] are of current and potential economic value, respectively. Detailed geochemical analysis across the basin can aid in the understanding of the depositional environment, sedimentary processes, and water-chemistry evolution in this system. Quantitative geochemical data for Green River oil shale from the Piceance Basin of Colorado were collected by inductively coupled plasma optical emission spectroscopy and mass spectrometry as part of this study. The basin margin is represented by samples from exposures at Douglas Pass (Garfield County) and the basin center area is characterized by core samples from two drilled wells: the Shell 23X-2 and John Savage 24-1 (Rio Blanco County). Major elements and groups of elements are used as proxies for clastic influx (Si, Al, K, Ti), carbonate deposition (Ca, Mg), salinity (Na), paleo-productivity (P), and redox state (Fe, S), respectively. Minor and trace elements reinforce observations based on major elements, including Rb, Zr, Nb for clastic influx and Mn, Sr for carbonate. Trace elements are used to characterize redox conditions (As, Mo, U, V, Co, Ni, Cu, Zn) and salinity (Rb/K, B/Ga). Chemical distinctions between the basin margin and the basin center, in terms of these components and total organic carbon concentrations, support the model of a permanently stratified lake through most of the depositional interval. A primary purpose of the study was to conduct more extensive sampling to confirm conclusions of a previous reconnaissance study. Geochemical data from this study indicates elevated Na around the basin margin occurring earlier than in the deeper basin. Early in the history of Lake Uinta, the salinity may have been elevated first in the shallower marginal waters, due to increased evaporation, which then led to elevated salinity in the basin center through transport of saline density currents. Other indicators of salinity (Rb/K, B/Ga) do not track Na content in intervals where clay minerals are absent due to diagenetic alteration under hypersaline conditions but may be used to indicate the salinities at which authigenic Na-bearing minerals begin to form. Most Na-rich samples show high proportions of clastic constituents (Si, Al, K, Ti) compared to conventional carbonate constituents (Ca, Mg). Redox-sensitive period IV transition metal elements (V, Co, Ni, Cu, Zn) show only local occurrence of significant enrichment relative to average shale abundances. Analysis of Fe/Al ratios for this dataset suggests that the depletion of these elements may be related to source rocks depleted in mafic constituents, with apparent redox-related enrichments subdued by this effect. The basin margin samples reflect generally oxic bottom waters, with some intervals deposited under more reducing, possibly dysoxic to anoxic conditions. The basin center results indicate more reducing conditions, with Mo and U enrichment factors suggesting operation of a particulate shuttle mechanism that scavenged Mo on Fe/Mn-oxyhydroxides that redissolved at depth, with Mo precipitating along with sulfides and/or organic matter at or near the sediment/water interface.

Colorado↗

USGS2015

Curiosity’s robotic arm-mounted Mars Hand Lens Imager (MAHLI): Characterization and calibration status

MAHLI (Mars Hand Lens Imager) is a 2-megapixel, Bayer pattern color CCD camera with a macro lens mounted on a rotatable turret at the end of the 2-meters-long robotic arm aboard the Mars Science Laboratory rover, Curiosity. The camera includes white and longwave ultraviolet LEDs to illuminate targets at night. Onboard data processing services include focus stack merging and data compression. Here we report on the results and status of MAHLI characterization and calibration, covering the pre-launch period from August 2008 through the early months of the extended surface mission through February 2015. Since landing in Gale crater in August 2012, MAHLI has been used for a wide range of science and engineering applications, including distinction among a variety of mafic, siliciclastic sedimentary rocks; investigation of grain-scale rock, regolith, and eolian sediment textures and structures; imaging of the landscape; inspection and monitoring of rover and science instrument hardware concerns; and supporting geologic sample selection, extraction, analysis, delivery, and documentation. The camera has a dust cover and focus mechanism actuated by a single stepper motor. The transparent cover was coated with a thin film of dust during landing, thus MAHLI is usually operated with the cover open. The camera focuses over a range from a working distance of 2.04 cm to infinity; the highest resolution images are at 13.9 µm per pixel; images acquired from 6.9 cm show features at the same scale as the Mars Exploration Rover Microscopic Imagers at 31 µm/pixel; and 100 µm/pixel is achieved at a working distance of ~26.5 cm. The very highest resolution images returned from Mars permit distinction of high contrast silt grains in the 30–40 µm size range. MAHLI has performed well; the images need no calibration in order to achieve most of the investigation’s science and engineering goals. The positioning and repeatability of robotic arm placement of the MAHLI camera head have been excellent on Mars, often with the hardware arriving within millimeters of expectation. Stability while imaging is usually such that the images are sharply focused; some exceptions—thought to result from motion induced by wind—have occurred during longer exposure LED-illuminated night imaging. Image calibration includes relative radiometric correction by removal of dark current and application of a flat field. Dark current is negligible to minor for typical daytime exposure durations and temperatures at the Gale field site. A pre-launch flat field product is usually applied to the data but new products created from images acquired by MAHLI of the Martian sky are superior and can provide a relative radiometric accuracy of ~6%. The camera lens imparts negligible distortion to its images; camera models derived from pre-launch data, with CAHV and CAHVOR parameters captured in their archived labels, can be applied to the images for analysis. MAHLI data and derived products, including pre-launch images, are archived with the NASA Planetary Data System (PDS). This report includes supplementary calibration and characterization data that are not available in the PDS archive (see supplement file MAHLITechRept0001_Supplement.zip).

MSL MAHLI Technical Report↗