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At least 199 records · Page 11Linked to original sources
USGS2004

Chapter 21 Western phosphate field - Depositional and economic deposit models

The Western Phosphate Field (WPF), composed of Permian marine sedimentary strata that cover over 300,000 km 2 in the middle Rocky Mountains of Idaho, Montana, Utah, and Wyoming in the United States, contains vast resources of phosphate mined for fertilizer and a range of other industrial applications. The richest deposits of phosphate in the WPF occur in the Meade Peak Phosphatic Shale Member of the Phosphoria Formation in southeast Idaho. Phosphate is an essential and even limiting nutrient of algal production, which occurs at the bottom of the marine food web in the oceanic photic zone. The high concentrations of phosphate and trace elements in the Phosphoria Formation reflect a low accumulation rate of diluting phases, such as terrigenous siliciclastic debris and carbonate, rather than an unusually high level of primary productivity at the time of deposition. Indeed, the mean rate of accumulation of PO 4 3 required a continuous flux of PO 4 3 into the basin and the photic zone of the water column, but only at a moderate level. This flux was maintained by upwelling of nutrient-rich seawater, imported at depth from the open ocean. Although only a fraction of the organic matter that hosted the PO 4 3 and other nutrients (NO 3 , Cd, Cu, Mo, Ni, and Zn) actually escaped oxidation in the water column, their rate of accu- mulation on the sea floor defined the basin hydrography. Rates of accumulation of Cr, U, V, and rare-earth elements by precipitation and adsorp- tion reactions identify redox conditions in the bottom water as having been denitrifying, maintained by a balance between the rate of oxidation of organic matter settling through the water column and the flux of open-ocean seawater at depth. Atmospheric mixing maintained oxygen respiration in the uppermost several tens of meters of the water column. This hydrography and seawater chemistry are present in several sedimentary envi- ronments in the ocean today. In the WPF, there is an estimated surface mineable reserve base and subeconomic resource of 7.6 billion mt, at an average grade of 24% P 2 O 5 ; a subeconomic underground- mineable resource of 17 billion mt, at a grade of 28%; and 507 billion mt of subresource- grade phosphatic material that underlie the WPF at a depth greater than 305 m. The relationship between phosphate-ore specifications and weathering suggests that significant changes in processing, with associated cost increases, will be required to extend recovery of ore below the relatively strongly weathered zone near the surface. Four open pit mines currently extract phosphate from two moderately to steeply dipping ore zones that typically contain between 20% and 35% P 2 O 5 . Although the shales are enriched in trace elements, especially As, Cd, Cr, Cu, Mo, Se, U, V, Zn, and rare-earth elements, the relative concentration of organic carbon and selected major element oxides determines the suitability of phosphate-rich rock for feed to processing plants and its other applications. Selected specifications from the four operating mines include the following: minimum P 2 O 5 of 18-20% and average of 26-27%; maximum A1 2 O 3 of 1.6-5.0%; maximum MgO of 0.3-0.6%; a CaO/P 2 O 5 ratio of 1.5-1.6; and total carbon content of 4%-5%. Weathering to a depth of as much as 100 m significantly enhances ore quality by decreasing the proportions of calcite, dolomite, and organic matter relative to carbonate fluorapatite, the primary ore mineral

Colorado, Idaho, Montana, Nebraska, North Dakota, ↗
USGS2014

Geologic implications of gas hydrates in the offshore of India: results of the National Gas Hydrate Program Expedition 01

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) is designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula and in the Andaman convergent margin, with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. The NGHP-01 expedition established the presence of gas hydrates in the Krishna-Godavari and Mahanadi Basins, and the Andaman Sea. The expedition discovered in the Krishna-Godavari Basin one of the thickest gas hydrate accumulations ever documented, in the Andaman Sea one of the thickest and deepest gas hydrate stability zones in the world, and established the existence of a fully developed gas hydrate petroleum system in all three basins. The primary goal of NGHP-01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India. This was done in order to meet the long-term goal of exploiting gas hydrate as a potential energy resource in a cost effective and safe manner. During its 113.5-day voyage, the D/V JOIDES Resolution cored and/or drilled 39 holes at 21 sites (1 site in Kerala-Konkan, 15 sites in Krishna-Godavari, 4 sites in Mahanadi, and 1 site in the Andaman deep offshore area), penetrated more than 9250 m of sedimentary section, and recovered nearly 2850 m of core. Twelve holes were logged with logging-while-drilling (LWD) tools and an additional 13 holes were wireline logged. The science team utilized extensive on-board laboratory facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Samples were also analyzed in additional post-expedition shore-based studies conducted in leading laboratories around the world. One of the specific objectives of this expedition was to test gas hydrate formation models and constrain model parameters, especially those that account for the formation of concentrated gas hydrate accumulations. The necessary data for characterizing the occurrence of in situ gas hydrate, such as interstitial water chlorinities, core-derived gas chemistry, physical and sedimentological properties, thermal images of the recovered cores, and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-01. Almost all of the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites drilled during NGHP-01 indicate that the occurrence of concentrated gas hydrate is mostly associated with the presence of fractures in the sediments, and in some limited cases, by coarser grained (mostly sand-rich) sediments.

Marine and Petroleum Geology↗
USGS2002

Mantle helium and carbon isotopes in Separation Creek geothermal springs, Three Sisters area, central Oregon: Evidence for renewed volcanic activity or a long term steady state system?

Here we present the helium and carbon isotope results from the initial study of a fluid chemistry-monitoring program started in the summer of 2001 near the South Sister volcano in central Oregon. The Separation Creek area which is several miles due west of the volcano is the locus of strong crustal uplift currently occurring at a rate of 4-5 cm/yr (Wicks, et. al. , 2001). Helium [R C /R A = 7.44 and 8.61 R A (R C /R A = ( 3 He/ 4 He) sample-air corrected /( 3 He/ 4 He) air ))] and carbon (δ 13 C = -11.59 to -9.03 ‰ vs PDB) isotope data and CO 2 / 3 He (5 and 9 x 10 9 ) show that bubbling cold springs in the Separation Creek area near South Sister volcano carry a strong mantle signal, indicating the presence of fresh basaltic magma in the volcanic plumbing system. There is no evidence though, to directly relate this signal to the crustal uplift that is currently taking place in the area, which started in 1998. The geothermal system in the area is apparently much longer lived and shows no significant changes in chemistry compared to data from the early 1990s. Hot springs in the area, which are relatively far removed from the volcanic edifice, do not carry a strong mantle signal in helium isotope ratios (2.79 to 5.08 R A ), unlike the cold springs, and also do not show any significant changes in helium isotope ratios compared to literature data for the same springs of over two decades ago. The cold springs of the Separation Creek area form a very diffuse but significant low temperature geothermal system, that should, due to its close vicinity to the center of up uplift, be more sensitive to changes in the deeper volcanic plumbing system than the far removed hot springs and therefore require much more study and consideration when dealing with volcano monitoring in the Cascade range or possibly with geothermal exploration in general.

Oregon↗
USGS2007

Occurrence of Uranium and 222Radon in Glacial and Bedrock Aquifers in the Northern United States, 1993-2003

Water-quality data collected from 1,426 wells during 1993-2003 as part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) program were evaluated to characterize the water quality in glacial and bedrock aquifers of the northern United States. One of the goals of the NAWQA program is to synthesize data from individual studies across the United States to gain regional- and national-scale information about the behavior of contaminants. This study focused on the regional occurrence and distribution of uranium and 222radon in ground water in the glacial aquifer system of the United States as well as in the Cambrian-Ordovician and the New York and New England crystalline aquifer systems that underlie the glacial aquifer system. The occurrence of uranium and 222radon in ground water has long been a concern throughout the United States. In the glacial aquifers, as well as the Cambrian-Ordovician and the New York and New England crystalline aquifer systems of the United States, concentrations of uranium and 222radon were highly variable. High concentrations of uranium and 222radon affect ground water used for drinking water and for agriculture. A combination of information or data on (1) national-scale ground-water regions, (2) regional-scale glacial depositional models, (3) regional-scale geology, and (4) national-scale terrestrial gamma-ray emissions were used to confirm and(or) refine the regions used in the analysis of the water-chemistry data. Significant differences in the occurrence of uranium and 222radon, based primarily on geologic information were observed and used in this report. In general, uranium was highest in the Columbia Plateau glacial, West-Central glacial, and the New York and New England crystalline aquifer groups (75th percentile concentrations of 22.3, 7.7, and 2.9 micrograms per liter (ug/L), respectively). In the Columbia Plateau glacial and the West-Central glacial aquifer groups, more than 10 percent of wells sampled had concentrations of uranium that exceeded the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level of 30 ug/L; in the New York and New England crystalline aquifer group, 4 percent exceeded 30 ug/L. Ground-water samples with high concentrations of uranium were commonly linked to geologic sources rich in uranium. In eight of nine aquifer groups defined for this study, concentrations of uranium correlated significantly with concentrations of sulfate in ground water (Spearman's rho = 0.20 to 0.56; p < 0.05). In the Columbia Plateau, glacial aquifers were derived in part from basaltic lava flows, some felsic volcanic rocks, and some paleo-lake bed materials that may be rich in uranium. In the Columbia Plateau and West-Central glacial aquifer groups, uranium correlated with total dissolved solids, bicarbonate, boron, lithium, selenium, and strontium. In the West-Central glacial aquifer group, rocks such as Cretaceous marine shales, which are abundant in uranium, probably contribute to the high concentrations in ground water; in the southern part of this group, which extends into Nebraska, the glacial or glacial-related sediment may be interbedded with uranium-rich materials that originated to the north and west and in the Rocky Mountains. In New England, crystalline bedrock that is granitic, such as two-mica granites, as well as other high-grade metamorphic rocks, has abundant uranium that is soluble in the predominantly oxic to sub-oxic geochemical conditions. This appears to contribute to high uranium concentrations in ground water. The highest 222radon concentrations were present in samples from wells completed in the New York and New England crystalline aquifer group; the median value (2,122 picocurries per liter (pCi/L)) was about 10 times the median values of all other aquifer groups. More than 25 percent of the samples from the New York and New England crystalline aquifer group wells had 222radon concentrations that exceeded the USEPA Alternative

Scientific Investigations Report↗
USGS1989

Geochemistry and diagenesis of Miocene lacustrine siliceous sedimentary and pyroclastic rocks, Mytilinii basin, Samos Island, Greece

A Late Miocene non-marine stratigraphic sequence composed of limestone, opal-CT-bearing limestone, porcelanite, marlstone, diatomaceous marlstone, dolomite, and tuffite crops out on eastern Samos Island. This lacustrine sequence is subdivided into the Hora Beds and the underlying Pythagorion Formation. The Hora Beds is overlain by the clastic Mytilinii series which contains Turolian (Late Miocene) mammalian fossils. The lacustrine sequence contains volcanic glass and the silica polymorphs opal-A, opal-CT, and quartz. Volcanic glass predominantly occurs in tuffaceous rocks from the lower and upper parts of the lacustrine sequence. Opal-A (diatom frustules) is confined to layers in the upper part of the Hora Beds. Beds rich in opal-CT underlie those containing opal-A. The occurrence of opal-CT is extensive, encompassing the lower Hora Beds and the sedimentary rocks and tuffs of the Pythagorion Formation. A transition zone between the opal-A and opal-CT zones is identified by X-ray diffraction patterns that are intermediate between those of opal-CT and opal-A, perhaps due to a mixture of the two polymorphs. Diagenesis was not advanced enough for opal-CT to transform to quartz or for volcanic glass to transform to opal-C. Based on geochemical and mineralogical data, we suggest that the rate of diagenetic transformation of opal-A to opal-CT was mainly controlled by the chemistry of pore fluids. Pore fluids were characterized by high salinity, moderately high alkalinity, and high magnesium ion activity. These pore fluid characteristics are indicated by the presence of evaporitic salts (halite, sylvite, niter), high boron content in biogenic silica, and by dolomite in both the opal-A and opal-CT-bearing beds. The absence of authigenic K-feldspar, borosilicates, and zeolites also support these pore fluid characteristics. Additional factors that influenced the rate of silica diagenesis were host rock lithology and the relatively high heat flow in the Aegean region from Miocene to Holocene.

Samos Island↗
USGS2016

Sediment chemistry and toxicity in Barnegat Bay, New Jersey: Pre- and post-Hurricane Sandy, 2012–13

Hurricane Sandy made landfall in Barnegat Bay, October, 29, 2012, damaging shorelines and infrastructure. Estuarine sediment chemistry and toxicity were investigated before and after to evaluate potential environmental health impacts and to establish post-event baseline sediment-quality conditions. Trace element concentrations increased throughout Barnegat Bay up to two orders of magnitude, especially north of Barnegat Inlet, consistent with northward redistribution of silt. Loss of organic compounds, clay, and organic carbon is consistent with sediment winnowing and transport through the inlets and sediment transportmodeling results. The number of sites exceeding sediment quality guidance levels for trace elements tripled post-Sandy. Sediment toxicity post-Sandy was mostly unaffected relative to pre-Sandy conditions, but at the site with the greatest relative increase for trace elements, survival rate of the test amphipod decreased (indicating degradation). This study would not have been possible without comprehensive baseline data enabling the evaluation of storm-derived changes in sediment quality.

New Jersey↗
USGS2016

Comparison of wastewater-associated contaminants in the bed sediment of Hempstead Bay, New York, before and after Hurricane Sandy

Changes in bed sediment chemistry of Hempstead Bay (HB) have been evaluated in the wake of Hurricane Sandy, which resulted in the release of billions of liters of poorly-treated sewage into tributaries and channels throughout the bay. Surficial grab samples (top 5 cm) collected before and (or) after Hurricane Sandy from sixteen sites in HB were analyzed for 74 wastewater tracers and steroid hormones, and total organic carbon. Data from pre- and post-storm comparisons of the most frequently detected wastewater tracers and ratios of steroid hormone and of polycyclic aromatic hydrocarbon concentrations indicate an increased sewage signal near outfalls and downstream of where raw sewage was discharged. Median concentration of wastewater tracers decreased after the storm at sites further from outfalls. Overall, changes in sediment quality probably resulted from a combination of additional sewage inputs, sediment redistribution, and stormwater runoff in the days to weeks following Hurricane Sandy.

New York↗
USGS1995

Inter-relation of cytochrome P450 and contaminants burdens in sibling heron embryos and nestlings

Hepatic cytochrome P450-associated monooxygenase activities were measured in 11-day-old nestling black-crowned night-herons (Nycticorax nycticorax) collected from a reference site (next to the Chincoteague National Wildlife Refuge, Virginia) and three polluted sites (Cat Island, Green Bay, Lake Michigan, Wisconsin; Bair Island, San Francisco Bay, California; West Marin Island, San Francisco Bay, California). Activities of arylhydrocarbon hydroxylase (AHH) and benzyl-oxyresorufin-O-dealkylase (BROD) weremodestly elevated (<three-fold) in nestlings from polluted sites. Concentrations of p,p?DDE, other organochlorinepesticides and total PCBs in nestlings were greatest at contaminated sites, although much lower than found in concurrently collected eggs and pipping embryos. At these low pollutant concentrations there was little correlation between monooxygenase activity and contaminant levels in nestlings. These observations markedly contrast the pronounced monooxygenase induction (up to 85-fold) and its significant correlation with total PCBs, arylhydrocarbon receptor-active PCB congeners and toxic equivalents in concurrently collected night-heron embryos that were often siblings of the nestlings. The present findings suggest that cytochrome P450-associated monooxygenase activity of heron nestlings may have only limited value as a biomarker of exposure at this rapid-growth life stage.

Society of Environmental Toxicology and Chemistry,↗
USGS1996

Cytochrome P450 and contaminant concentrations in nestling black-crowned night-herons and their interrelation with sibling embryos

Hepatic cytochrome P450-associated monooxygenase activities were measured in 11-d-old nestling black-crowned night-herons ( Nycticorax nycticorax ) collected from a reference site (next to Chincoteague National Wildlife Refuge, VA, USA) and three contaminated sites (Cat Island, Green Bay, WI, USA; Bair Island, San Francisco Bay, CA, USA; and West Marin Island, San Francisco Bay, CA, USA). Arylhydrocarbon hydroxylase and benzyloxyresorufin- O -dealkylase activities of nestlings from contaminated sites were only slightly elevated (less than threefold) compared with the reference site. Organochlorine pesticide and total polychlorinated biphenyl (PCB) concentrations in nestlings were greatest at contaminated sites, although much lower than found in concurrently collected eggs and pipping embryos. Pollutant concentrations of nestlings were rarely associated with monooxygenase activity. In contrast, concurrently collected pipping heron embryos (often siblings of the nestlings) exhibited pronounced monooxygenase induction (means at contaminated sites were elevated up to sevenfold and values of some embryos exceeded 25-fold induction). Furthermore, monooxygenase activity of pipping embryos was significantly correlated with total PCBs, arylhydrocarbon receptor-active PCB congeners, and toxic equivalents. The modest monooxygenase responses of heron nestlings suggest that this biomarker may have only limited value during this rapid-growth life stage.

California, Virginia, Wisconsin↗
USGS2019

Physicochemical controls on zones of higher coral stress where Black Band Disease occurs at Mākua Reef, Kauaʻi, Hawaiʻi

Pervasive and sustained coral diseases contribute to the systemic degradation of reef ecosystems, however, to date an understanding of the physicochemical controls on a coral disease event is still largely lacking. Water circulation and residence times and submarine groundwater discharge all determine the degree to which reef organisms are exposed to the variable chemistry of overlying waters; understanding these physical controls is thus necessary to interpret spatial patterns in coral health. The recent discovery of coral Black Band Disease at Mākua Reef on Kauaʻi, Hawaiʻi prompted an investigation into the physicochemical drivers and geomorphic controls of reef water circulation, and the temporally variable nutrient fluxes derived from submarine groundwater discharge. Results reveal localized stagnant water parcels at Mākua Reef where groundwater-derived high nutrient loading and low salinities act in concert as stressors to coralline health – and where Black Band Disease was uniquely identified. The observed high nutrient levels during low tide conditions are likely associated with nearby upstream cesspools and drain fields. Information obtained using such a multidisciplinary approach has direct value for successful management of coastal aquifers and the health and sustainability of adjacent nearshore coral reef ecosystems.

Hawaii↗
USGS1985

Hydrologic and geochemical monitoring in Long Valley caldera, Mono County, California, 1982-1984

The Long Valley caldera is a potentially active volcanic area on the eastern side of the Sierra Nevada in east-central California. Hydrologic and geochemical monitoring of surface and subsurface features began in July 1982 to determine if changes were occurring in response to processes causing earthquakes and crustal deformation. Differences since 1982 in fluid chemistry of springs has been minor except at Casa Diablo, where rapid fluctuations in chemistry result from near surface boiling and mixing. Ratios of 3 He/ 4 He and 13 C/ 12 C in hot springs and fumaroles are consistent with a magnetic source for some of the carbon and helium discharged in thermal areas, and observed changes in 3 He/ 4 He between 1978 and 1984 suggest changes in the magmatic component. Significant fluctuations in hot spring discharge recorded at several sites since 1982 closely followed earthquake activity. Water levels in wells have been used as strain meters to detect rock deformation associated with magmatic and tectonic activity and to construct a water table contour map. Coseismic water level fluctuations of as much as 0.6 ft have been observed but no clear evidence of deformation caused by magmatic intrusions can be seen in the well records through 1984. Temperature profiles in wells, which can be used to delineate regionally continuous zones of lateral flow of hot water across parts of the caldera, have remained constant at all but two sites.

California↗
USGS1998

Development and application of a marine sediment pore-water toxicity test using Ulva fasciata zoospores

An acute (96 h) pore-water toxicity test protocol using germination and growth of Ulva fasciata zoospores as endpoints was developed to test the toxicity of marine and estuarine sediment pore-water samples. Tests with an organic toxicant (sodium dodecyl sulfate; SDS), three metals (Cd, Cu, and Zn), and ammonia (NH 3 ) were conducted to determine zoospore sensitivity. Zoospore germination and gametophyte growth were as sensitive to SDS as sea urchin ( Arbacia punctulata ) fertilization and embryological development. Zoospore sensitivity to metals was greater than or comparable to that of adult macroalgae. Zoospores were less sensitive to NH 3 than were other commonly used toxicity test organisms. Test results using this algal assay with sediment pore-water samples with high NH 3 concentrations were compared with results from sea urchin fertilization and embryological development tests for the same samples. Ulva fasciata zoospore germination was not affected by samples with high NH 3 concentrations that were toxic in both sea urchin tests. Zoospore tolerance of NH 3 and sensitivity to other contaminants indicate that their response may be useful in toxicity identification evaluation studies with pore-water samples that contain high concentrations of unionized NH 3 .

Environmental Toxicology and Chemistry↗
USGS2005

Systematics of halogen elements and their radioisotopes in thermal springs of the Cascade Range, Central Oregon, Western USA

This study quantifies the cycling of halogen elements through the Cascadia subduction zone based on the chemistry of thermal springs in the Central Oregon Cascade Range and of a mineral spring in the forearc (Willamette Valley). Considerations based on mass balances, element ratios, and 36 Cl/Cl and 129 I/I ratios suggest that halogens discharged through the thermal springs in the Cascade Range are probably derived from magma degassing. Our results indicate that < 35% of the subducted Cl and < 20% of the subducted Br and I could be transported through arc volcanism and the thermal springs, a considerably lower percentage than estimated for other volcanic arcs along the Pacific Rim. A likely explanation for this difference is that a large fraction of the halogens is released from the slab at shallow depths into the serpentinized sub-forearc mantle because of the relatively high temperatures in the subducting Juan de Fuca plate. The small fraction of halogens subducted to depth probably also indicates a low rate of water transport, which is consistent with the observation that the Cascade Range sub-arc mantle is relatively dry and has a low degree of volcanic vigor, compared with other arcs.

Oregon↗
USGS2013

Springs, streams, and gas vent on and near Mount Adams volcano, Washington

Springs and some streams on Mount Adams volcano have been sampled for chemistry and light stable isotopes of water. Spring temperatures are generally cooler than air temperatures from weather stations at the same elevation. Spring chemistry generally reflects weathering of volcanic rock from dissolved carbon dioxide. Water in some springs and streams has either dissolved hydrothermal minerals or has reacted with them to add sulfate to the water. Some samples appear to have obtained their sulfate from dissolution of gypsum while some probably involve reaction with sulfide minerals such as pyrite. Light stable isotope data for water from springs follow a local meteoric water line, and the variation of isotopes with elevation indicate that some springs have very local recharge and others have water from elevations a few hundred meters higher. No evidence was found for thermal or slightly thermal springs on Mount Adams. A sample from a seeping gas vent on Mount Adams was at ambient temperature, but the gas is similar to that found on other Cascade volcanoes. Helium isotopes are 4.4 times the value in air, indicating that there is a significant component of mantle helium. The lack of fumaroles on Mount Adams and the ambient temperature of the gas indicates that the gas is from a hydrothermal system that is no longer active.

Washington↗
USGS2020

Sphalerite oxidation in seawater with covellite: Implications for seafloor massive sulfide deposits and mine waste

Metal sulfide minerals exist in several marine environments and are in thermodynamic disequilibrium with oxygenated seawater from the time of their formation. Oxidation is both ubiquitous and heterogeneous, as observational and experimental evidence demonstrates that sulfide minerals may oxidize completely on decadal timescales (hydrothermal plumes) or incompletely in billions of years (mineral deposits); however, the processes, rates, and interactions among minerals as oxidative dissolution occurs are not well understood. Added impetus to understanding these processes exists due to the potential for mining of seafloor massive sulfide deposits and potential environmental impacts of that activity. Here, we present a laboratory-based experimental study on the galvanic oxidation of sphalerite and synthesized zinc sulfide and coupled to covellite. We find that, in contrast to single-mineral reactions, coupled mineral reactions are at least 2 orders of magnitude more rapid, light independent, and have a lower apparent activation energy for oxidation. These results begin to provide insight into observed differences between laboratory and environmentally observed oxidation rates and are a step in the direction of more accurately predicting environmental rates as well as any changes to those rates from anthropogenic disturbances.

ACS Earth and Space Chemistry↗
USGS1999

Crustal and lithospheric structure of the west Antarctic Rift System from geophysical investigations: A review

The active West Antarctic Rift System, which extends from the continental shelf of the Ross Sea, beneath the Ross Ice Shelf and the West Antarctic Ice Sheet, is comparable in size to the Basin and Range in North America, or the East African rift systems. Geophysical surveys (primarily marine seismic and aeromagnetic combined with radar ice sounding) have extended the information provided by sparse geologic exposures and a few drill holes over the ice and sea covered area. Rift basins developed in the early Cretaceous accompanied by the major extension of the region. Tectonic activity has continued episodically in the Cenozoic to the present, including major uplift of the Transantarctic Mountains. The West Antarctic ice sheet, and the late Cenozoic volcanic activity in the West Antarctic Rift System, through which it flows, have been coeval since at least Miocene time. The rift is characterized by sparse exposures of late Cenozoic alkaline volcanic rocks extending from northern Victoria Land throughout Marie Byrd Land. The aeromagnetic interpretations indicate the presence of > 5 x 105 km2 (> 106 km3) of probable late Cenozoic volcanic rocks (and associated subvolcanic intrusions) in the West Antarctic rift. This great volume with such limited exposures is explained by glacial removal of the associated late Cenozoic volcanic edifices (probably hyaloclastite debris) concomitantly with their subglacial eruption. Large offset seismic investigations in the Ross Sea and on the Ross Ice Shelf indicate a ~ 17-24-km-thick, extended continental crust. Gravity data suggest that this extended crust of similar thickness probably underlies the Ross Ice Shelf and Byrd Subglacial Basin. Various authors have estimated maximum late Cretaceous-present crustal extension in the West Antarctic rift area from 255-350 km based on balancing crustal thickness. Plate reconstruction allowed < 50 km of Tertiary extension. However, paleomagnetic measurements suggested about 1000 km of post-middle Cretaceous translation between East Antarctica and Pacific West Antarctica. Because a great amount of crustal extension in late Cenozoic time is unlikely, alternate mechanisms have been proposed for the late Cenozoic volcanism. Its vast volume and the ocean island basalt chemistry of the exposed late Cenozoic alkaline volcanic rocks were interpreted as evidence for a mantle plume head. An alternative or supplemental explanation to the mantle plume hypothesis is significantly greater lower lithosphere (mantle) stretching resulting in greater decompression melting than the limited Cenozoic crustal extension allows. Because of very slow rates of late Cenozoic extension in the West Antarctic Rift System, the amount of advected heat is small compared with the conductive heat. Therefore, phase transition probably would not explain the large subsidence with low extension observed in the West Antarctic Rift System.

Global and Planetary Change↗
USGS2008

Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico

Pore waters extracted from 18 piston cores obtained on and near a salt-cored bathymetric high in Keathley Canyon lease block 151 in the northern Gulf of Mexico contain elevated concentrations of chloride (up to 838 mM) and have pore water chemical concentration profiles that exhibit extensive departures (concavity) from steady-state (linear) diffusive equilibrium with depth. Minimum ??13C dissolved inorganic carbon (DIC) values of -55.9??? to -64.8??? at the sulfate-methane transition (SMT) strongly suggest active anaerobic oxidation of methane (AOM) throughout the study region. However, the nonlinear pore water chemistry-depth profiles make it impossible to determine the vertical extent of active AOM or the potential role of alternate sulfate reduction pathways. Here we utilize the conservative (non-reactive) nature of dissolved chloride to differentiate the effects of biogeochemical activity (e.g., AOM and/or organoclastic sulfate reduction) relative to physical mixing in high salinity Keathley Canyon sediments. In most cases, the DIC and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the SMT as endmembers. Conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water-depth profiles. In limited cases where the sulfate and DIC concentrations deviated from conservative mixing between the seafloor and SMT, the ??13C-DIC mixing diagrams suggest that the excess DIC is produced from a 13C-depleted source that could only be accounted for by microbial methane, the dominant form of methane identified during this study. We conclude that AOM is the most prevalent sink for sulfate and that it occurs primarily at the SMT at this Keathley Canyon site.

Marine and Petroleum Geology↗
USGS2008

Exposure of mallards (Anas platyrhynchos) to the hepatotoxic cyanobacterium Nodularia spumigena

Nodularin (NODLN) is a cyclic pentapeptide hepatotoxin produced by the cyanobacterium Nodularia spumigena, which forms extensive blooms during the summer in the Baltic Sea. Nodularin was detected in liver, muscle and/or feather samples of several common eiders (Somateria mollissima) from the Gulf of Finland (northern Baltic Sea) in 2002-2005. Published information on the adverse effects of NODLN in marine birds is scarce. The aim of this study was to evaluate the toxicity of NODLN, and determine the concentrations of NODLN in liver and muscle tissue in mallards (Anas platyrhynchos) exposed to N. spumigena. Mallards received a single or multiple exposure via oral gavage with an aqueous slurry containing toxic N. spumigena. Dosages ranged from 200 to 600 ??g NODLN per kg body weight (bw). There were minimal histopathological changes in liver tissue, and brain cholinesterase activity did not differ among treatment groups. Concentrations of NODLN measured by LC-MS in liver varied between approximately 3-120 ??g kg-1 dry weight (dw) and ducks receiving multiple exposures had significantly greater liver toxin levels than ducks receiving the two lowest single exposures. In muscle, NODLN concentrations were approximately 2-6 ??g kg-1 dw, but did not differ significantly among exposure groups. This is the first in vivo lab study examining the effects and bioaccumulation of NODLN from N. spumigena in birds. The mallards in this study were resistant to adverse effects and did not bioaccumulate substantial levels of NODLN at the doses given. ?? 2008 Taylor & Francis.

Gulf of Finland↗