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

USGS2008

Development of a three-dimensional, regional, coupled wave, current, and sediment-transport model

We are developing a three-dimensional numerical model that implements algorithms for sediment transport and evolution of bottom morphology in the coastal-circulation model Regional Ocean Modeling System (ROMS v3.0), and provides a two-way link between ROMS and the wave model Simulating Waves in the Nearshore (SWAN) via the Model-Coupling Toolkit. The coupled model is applicable for fluvial, estuarine, shelf, and nearshore (surfzone) environments. Three-dimensional radiation-stress terms have been included in the momentum equations, along with effects of a surface wave roller model. The sediment-transport algorithms are implemented for an unlimited number of user-defined non-cohesive sediment classes. Each class has attributes of grain diameter, density, settling velocity, critical stress threshold for erosion, and erodibility constant. Suspended-sediment transport in the water column is computed with the same advection-diffusion algorithm used for all passive tracers and an additional algorithm for vertical settling that is not limited by the CFL criterion. Erosion and deposition are based on flux formulations. A multi-level bed framework tracks the distribution of every size class in each layer and stores bulk properties including layer thickness, porosity, and mass, allowing computation of bed morphology and stratigraphy. Also tracked are bed-surface properties including active-layer thickness, ripple geometry, and bed roughness. Bedload transport is calculated for mobile sediment classes in the top layer. Bottom-boundary layer submodels parameterize wave-current interactions that enhance bottom stresses and thereby facilitate sediment transport and increase bottom drag, creating a feedback to the circulation. The model is demonstrated in a series of simple test cases and a realistic application in Massachusetts Bay.

Computers & Geosciences↗

USGS2004

Temporal changes in nitrogen adsorption properties of single-walled carbon nanotubes

Temporal evolution of N2 adsorption (77 K) properties of as-produced and purified single-walled nanotubes (SWNTs) samples is described here. The N2 adsorption isotherms are used to characterize the samples' surface areas and porosities. The as-produced samples demonstrate a temporal increase in surface area and pore volumes for up to 16 months. The purified samples, however, reached their stable values of surface area and pore volumes within four to seven months. N2 adsorption capacity of the purified SWNTs also increased when the fresh samples were subjected to thermal pre-processing, with diminishing changes in adsorption capacity with increased age. These observations indicate that the freshly prepared SWNTs, both as-produced and purified, were in an unstable state with their porosity changing with increasing sample age and thermal treatments. It is hypothesized that SWNTs undergo slow but progressive changes in their surface chemistry which causes their N2 adsorption properties to change over several months. ?? 2004 Elsevier Ltd. All rights reserved.

Carbon↗

USGS2006

Conservation of Toll-like receptor signaling pathways in teleost fish

In mammals, toll-like receptors (TLR) recognize ligands, including pathogen-associated molecular patterns (PAMPs), and respond with ligand-specific induction of genes. In this study, we establish evolutionary conservation in teleost fish of key components of the TLR-signaling pathway that act as switches for differential gene induction, including MYD88, TIRAP, TRIF, TRAF6, IRF3, and IRF7. We further explore this conservation with a molecular phylogenetic analysis of MYD88. To the extent that current genomic analysis can establish, each vertebrate has one ortholog to each of these genes. For molecular tree construction and phylogeny inference, we demonstrate a methodology for including genes with only partial primary sequences without disrupting the topology provided by the high-confidence full-length sequences. Conservation of the TLR-signaling molecules suggests that the basic program of gene regulation by the TLR-signaling pathway is conserved across vertebrates. To test this hypothesis, leukocytes from a model fish, rainbow trout ( Oncorhynchus mykiss ), were stimulated with known mammalian TLR agonists including: diacylated and triacylated forms of lipoprotein, flagellin, two forms of LPS, synthetic double-stranded RNA, and two imidazoquinoline compounds (loxoribine and R848). Trout leukocytes responded in vitro to a number of these agonists with distinct patterns of cytokine expression that correspond to mammalian responses. Our results support the key prediction from our phylogenetic analyses that strong selective pressure of pathogenic microbes has preserved both TLR recognition and signaling functions during vertebrate evolution.

Comparative Biochemistry and Physiology, Part D: G↗

USGS2005

Characterization of waste rock associated with acid drainage at the Penn Mine, California, by ground-based visible to short-wave infrared reflectance spectroscopy assisted by digital mapping

Prior to remediation at the abandoned Cu-Zn Penn Mine in the Foothills massive sulfide belt of the Sierra Nevada, CA, acid mine drainage (AMD) was created, in part, by the subaerial oxidation of sulfides exposed on several waste piles. To support remediation efforts, a mineralogical study of the waste piles was undertaken by acquiring reflectance spectra (measured in the visible to short-wave infrared range of light (0.35-2.5 ??m) using a portable, digitally integrated pen tablet PC mapping system with differential global positioning system and laser rangefinder support. Analysis of the spectral data made use of a continuum removal and band-shape comparison method, and of reference spectral libraries of end-member minerals and mineral mixtures. Identification of secondary Fe-bearing minerals focused on band matching in the region between 0.43 and 1.3 ??m. Identification of sheet and other silicates was based on band-shape analysis in the region between 1.9 and 2.4 ??m. Analysis of reflectance spectra of characterized rock samples from the mine helped in gauging the spectral response to particle size and mixtures. The resulting mineral maps delineated a pattern of accumulation of secondary Fe minerals, wherein centers of copiapite and jarosite that formed at low pH (<3) were surrounded successively by goethite and hematite, which mark progressive increases in pH. This pattern represents the evolution of acid solutions discharged from the pyritic waste piles and the subsequent accumulation of secondary precipitates by hydrolysis reactions. The results highlight the high capacity of the pyritic waste to release further acid mine drainage into the environment, as well as the effectiveness of the mapping method to detect subtle changes in surface mineralogy and to produce maps useful to agencies responsible for remediating the site. ?? 2004 Elsevier B.V. All rights reserved.

Chemical Geology↗

USGS2009

Changing sources of strontium to soils and ecosystems across the Hawaiian Islands

Strontium isotope ratios assist ecosystem scientists in constraining the sources of alkaline earth elements, but their interpretation can be difficult because of complexities in mineral weathering and in the geographical and environmental controls on elemental additions and losses. Hawaii is a "natural laboratory" where a number of important biogeochemical variables have either limited ranges or vary in systematic ways, providing a unique opportunity to understand the impact of time, climate, and atmospheric inputs on the evolution of base cation sources to ecosystems. There are three major sources of strontium (Sr) to these ecosystems, each with distinct isotopic compositions: basalt lava, Asian dust, and rainfall. We present Sr isotope and concentration data on both bulk soil digests and NH 4 Ac extracts from soil profiles covering a wide range of environments and substrate ages. Bulk soil material from dry climates and/or young substrate ages with > 80????g g - 1 Sr retain basalt-like Sr isotopic signatures, whereas those with Sr concentrations < 80????g g - 1 can have isotope signatures that range from basalt-like values to the more radiogenic values associated with continental dust. Although both dust accumulation and lava weathering are time- and rainfall-dependent, the overall concentration of Sr drops with increasing leaching even as quartz and mica derived from continental dust sources increase to > 40% by mass. At elevated dust levels, lava-derived Sr is low and dust-derived Sr is the dominant control of 87 Sr/ 86 Sr in bulk soils; however, 87 Sr/ 86 Sr of NH 4 Ac-extractable Sr largely reflects atmospheric deposition of marine aerosol in these situations. Overall, whole-soil Sr isotope values are controlled by complex interactions between Sr provided by lava weathering but partially lost by leaching, and Sr provided by dust but held in more resistant minerals. The isotopic composition of NH 4 Ac-extractable Sr and of the biota is controlled by lava weathering and rainfall contribution of Sr with only minor contributions from radiogenic dust sources. ?? 2009 Elsevier B.V.

Chemical Geology↗

USGS2009

Assessment of diel chemical and isotopic techniques to investigate biogeochemical cycles in the upper Klamath River, Oregon, USA

The upper Klamath River experiences a cyanobacterial algal bloom and poor water quality during the summer. Diel chemical and isotopic techniques have been employed in order to investigate the rates of biogeochemical processes. Four diel measurements of field parameters (temperature, pH, dissolved oxygen concentrations, and alkalinity) and stable isotope compositions (dissolved oxygen-?? 18 O and dissolved inorganic carbon-?? 13 C) have been performed between June 2007 and August 2008. Significant diel variations of pH, dissolved oxygen (DO) concentration, and DO-?? 18 O were observed, due to varying rates of primary productivity vs. respiration vs. gas exchange with air. Diel cycles are generally similar to those previously observed in river systems, although there are also differences compared to previous studies. In large part, these different diel signatures are the result of the low turbulence of the upper Klamath River. Observed changes in the diel signatures vs. sampling date reflect the evolution of the status of the algal bloom over the course of the summer. Results indicate the potential utility of applying diel chemical and stable isotope techniques to investigate the rates of biogeochemical cycles in slow-moving rivers, lakes, and reservoirs, but also illustrate the increased complexity of stable isotope dynamics in these low-turbulence systems compared to well-mixed aquatic systems. ?? 2009 Elsevier B.V.

Chemical Geology↗

USGS2013

Evaluation of Pleistocene groundwater flow through fractured tuffs using a U-series disequilibrium approach, Pahute Mesa, Nevada, USA

Groundwater flow through fractured felsic tuffs and lavas at the Nevada National Security Site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at Pahute Mesa. To help evaluate fracture flow and matrix–water exchange, we have determined U-series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces, breccia zones, and interiors of unfractured core. The U-series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium-series decay chain due to preferential mobilization of 234 U relative to 238 U, and U relative to Th. Samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays, silica, Fe–Mn oxyhydroxides, and zeolite. Intact core interiors and breccia fragments were sampled in bulk. In addition, profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture/matrix water exchange. Samples of rock matrix have 234 U/ 238 U and 230 Th/ 238 U activity ratios (AR) closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix. Greater U mobility was observed in welded-tuff matrix with elevated porosity and in zeolitized bedded tuff. Samples of brecciated core were also in secular equilibrium implying a lack of long-range hydraulic connectivity in these cases. Samples of discrete fracture surfaces typically, but not always, were in radioactive disequilibrium. Many fractures had isotopic compositions plotting near the 230 Th- 234 U 1:1 line indicating a steady-state balance between U input and removal along with radioactive decay. Numerical simulations of U-series isotope evolution indicate that 0.5 to 1 million years are required to reach steady-state compositions. Once attained, disequilibrium 234 U/ 238 U and 230 Th/ 238 U AR values can be maintained indefinitely as long as hydrological and geochemical processes remain stable. Therefore, many Pahute Mesa fractures represent stable hydrologic pathways over million-year timescales. A smaller number of samples have non-steady-state compositions indicating transient conditions in the last several hundred thousand years. In these cases, U mobility is dominated by overall gains rather than losses of U.

Nevada↗

USGS2014

Hydrogeochemistry of prairie pothole region wetlands: Role of long-term critical zone processes

This study addresses the geologic and hydrogeochemical processes operating at a range of scales within the prairie pothole region (PPR). The PPR is a 750,000 km 2 portion of north central North America that hosts millions of small wetlands known to be critical habitat for waterfowl and other wildlife. At a local scale, we characterized the geochemical evolution of the 92-ha Cottonwood Lake study area (CWLSA), located in North Dakota, USA. Critical zone processes are the long-term determinant of wetland water and groundwater geochemistry via the interaction of oxygenated groundwater with pyrite in the underlying glacial till. Pyrite oxidation produced a brown, iron oxide-bearing surface layer locally over 13 m thick and an estimated minimum of 1.3 × 10 10 g sulfate (SO 4 2 − ) at CWLSA. We show that the majority of this SO 4 2− now resides in solid-phase gypsum (CaSO 4 •2H 2 O) and gypsum-saturated groundwater. Results from the CWLSA were scaled up to a 9700 km 2 area surrounding CWLSA using ~ 1800 drill logs and literature data on wetland water chemistry for 178 wetlands within this larger area. The oxidized brown zone depth and wetland water compositional trends are very similar to the CWLSA. Additionally, surface water data from 176 southern Canadian pothole wetlands that conform to the same wetland water geochemical trends as those recorded in the CWLSA further corroborate that SO 4 2 − accumulation driven by pyrite oxidation is a nearly ubiquitous process in the prairie pothole region and distinguishes PPR wetlands from other wetlands worldwide that have a similar overall hydrology.

Manitoba, North Dakota, Saskatchewan↗

USGS2014

The curved 14 C vs. δ 13 C relationship in dissolved inorganic carbon: A useful tool for groundwater age- and geochemical interpretations

Determination of the 14 C content of dissolved inorganic carbon (DIC) is useful for dating of groundwater. However, in addition to radioactive decay, the 14 C content in DIC ( 14 C DIC ) can be affected by many geochemical and physical processes and numerous models have been proposed to refine radiocarbon ages of DIC in groundwater systems. Changes in the δ 13 C content of DIC (δ 13 C DIC ) often can be used to deduce the processes that affect the carbon isotopic composition of DIC and the 14 C value during the chemical evolution of groundwater. This paper shows that a curved relationship of 14 C DIC vs. δ 13 C DIC will be observed for groundwater systems if (1) the change in δ 13 C value in DIC is caused by a first-order or pseudo-first-order process, e.g. isotopic exchange between DIC and solid carbonate, (2) the reaction/process progresses with the ageing of the groundwater, i.e. with decay of 14 C in DIC, and (3) the magnitude of the rate of change in δ 13 C of DIC is comparable with that of 14 C decay. In this paper, we use a lumped parameter method to derive a model based on the curved relationship between 14 C DIC and δ 13 C DIC . The derived model, if used for isotopic exchange between DIC and solid carbonate, is identical to that derived by Gonfiantini and Zuppi (2003). The curved relationship of 14 C DIC vs. δ 13 C DIC can be applied to interpret the age of the DIC in groundwater. Results of age calculations using the method discussed in this paper are compared with those obtained by using other methods that calculate the age of DIC based on adjusted initial radiocarbon values for individual samples. This paper shows that in addition to groundwater age interpretation, the lumped parameter method presented here also provides a useful tool for geochemical interpretations, e.g. estimation of apparent rates of geochemical reactions and revealing the complexity of the geochemical environment.

Chemical Geology↗

USGS2023

High-precision ID-TIMS U-Pb geochronology of perovskite (CaTiO3) from the Ice River Complex, southeastern British Columbia

Uranium‑lead perovskite in situ geochronology has become a cornerstone technique for determining the emplacement timing of alkaline, ultrapotassic, and silica-undersaturated igneous rocks, kimberlites, and carbonatites. Accurate in situ dates are dependent on the availability of matrix matched mineral reference materials which themselves are chemically well characterized and dated accurately to the highest possible precision. When dating perovskite to high precision, such as by isotope dilution thermal ionization mass spectrometry (ID-TIMS), appropriately accounting and correcting for the quantity and isotopic composition of Pb incorporated into the crystal upon crystallization (Pb i ) is a large source of uncertainty and potential inaccuracy. Unfortunately, although ultra-high precision perovskite dates are attainable with modern mass spectrometry techniques, the accuracy of applied Pb i compositions, which can be a considerable percentage of total Pb in a crystal, has not kept pace, resulting in percent level inaccuracy on precisely measured isotopic ratios. In an effort to characterize the age and initial Pb isotopic composition of a readily available, relatively pure perovskite endmember (93–98%) which will be useful as a matrix matched age reference material for in situ U-Pb geochronology, we date crystals isolated from three samples from the Ice River Complex (samples 81IR6, I90.3, and I92.30) by ID-TIMS and evaluate their suitability as known-age reference materials. We directly determine the isotopic composition of Pb i in each sample by ID-TIMS measurement of cogenetic low 238 U/ 204 Pb (μ < 500) phlogopite, apatite, and/or clinopyroxene. Using these initial common Pb isotopic compositions, which are significantly more radiogenic than those predicted by age appropriate Pb evolution models, we obtain ultra-precise weighted-mean 206 Pb/ 238 U perovskite dates of 355.83 ± 0.14, 355.04 ± 0.15, and 357.34 ± 0.12 Ma on the three Ice River samples, respectively. These dates are consistent with the relative emplacement ages previously established for units in the Ice River layered ultramafic series based on field relationships. They also demonstrate the feasibility of attaining accurate perovskite dates in instances when maximum precision is critical by utilizing ID-TIMS analysis of cogenetic low uranium phases for direct measurement of Pb i .

British Columbia↗

USGS2026

The Sedimentary Geochemistry and Paleoenvironments Project Phase 2 data release: An open data resource for the study of Earth's environmental history

Geochemical data from sedimentary rocks are the primary source of information regarding Earth's surface evolution through time, including its air and water envelopes and interactions with life and deep Earth processes. The Sedimentary Geochemistry and Paleoenvironments Project (SGP) is a scientific consortium centered around open data and community-driven development of cyberinfrastructure tools and resources for sedimentary geochemistry and Earth history. Here we describe the SGP Phase 2 data release, which focused on incorporating Paleoproterozoic and Mesoproterozoic (2500–1000 million years ago) data and better accommodating carbonate data. This data release was built through the involvement of >200 researchers worldwide in academia, government, and industry, and provides the largest available public data resource for our user community in the academic fields of geochemistry, sedimentology, tectonics, paleontology, Earth history, and paleoclimate, as well as the petroleum and minerals industries. The dataset now encompasses 126,006 samples and 4,132,371 geochemical analyses. In addition to direct entry by SGP Team Members, we have ingested and incorporated datasets from the Geoscience Australia OZCHEM database, the Alberta Geological Survey, and the Deep-Time Marine Sedimentary Element Database (DM-SED) compilation. This paper details sampling in the Phase 2 dataset with respect to age, geography, lithology, and other geological characteristics, documents access via our search website and API, discusses possible issues and/or biases in the dataset that could impact analyses, describes plans for governance and stewardship of data from Indigenous lands, and serves as the citable reference paper for the data release.

Chemical Geology↗

USGS2026

Utilization of multiple geochronology techniques to constrain the age of laterization and mineralization of the world-class Mount Weld rare earth element deposit, Western Australia

Pervasive chemical weathering on stable cratons may form thick regoliths and elemental enrichment, but constraining the age of regolith formation is challenging. In this study we utilize multiple geochronological techniques on different minerals from the world-class Mount Weld rare earth element (REE) deposit, formed by lateritic weathering of a carbonatite, to constrain the age of formation and provide insight into landscape evolution. The oldest dates, ca. 100 to 38 Ma, are from Lu-Hf dating of churchite [HREE(PO 4 )·2(H 2 O)], a heavy REE phosphate mineral. Growth bands on individual minerals show a younging outwards. 40 Ar/ 39 Ar geochronology of cryptomelane [K(Mn 4+ ,Mn 2+ )₈O₁₆] yielded dates from ca. 40 to 27 Ma. Similarly, (U-Th)/He geochronology of goethite [FeO(OH)] yielded dates ranging from ca. 45 to 19 Ma. Integrating results into regional constraints, suggests 1) churchite formed by mineral saturation in a karst-like setting below the water table from ca. 100 to 40 Ma, 2) with minor uplift and erosion, cryptomelane and goethite formed at or near the water table between ca. 45 and 19 Ma, 3) after ca. 15 to 10 Ma chemical weathering within the profile had ended. Other studies document that the region experienced minimal uplift and a wet, warm climate from ca. 100 Ma to 15 Ma. These conditions and the high carbonate content of the carbonatite promote extensive chemical weathering, a deep weathering profile, and the preservation of the weathered section. This study highlights the use of multiple geochronological techniques utilizing different minerals to provide insight into how laterites form and to constrain the timing and history of the formation of this important mineral deposit.

Western Australia↗

USGS2026

Re-Os dating of paleozoic organic-rich black shales by LA-ICP-MS/MS

We present a new in-situ method for Re- Os geochronology of black shales using LA-ICP-MS/MS that is rapid, cost-effective, and sufficiently accurate and precise to address many geological questions. The method is tested on Paleozoic organic-rich black shales with independently constrained stratigraphic or radiometric ages. Results demonstrate that LA-ICP-MS/MS analysis yields Re- Os dates and initial Os isotopic compositions generally within uncertainty of published values using a laser spot size of 100 to 120 μ m in diameter. Despite low Os abundances in many samples, high-density microscale sampling compensates through large numbers of analyses, enabling robust inverse isochron regressions. The approach also allows contemporaneous acquisition of trace- element data (V, Ni, Mo and Re), providing insight into metal distribution in a sample, degree of metal enrichments, and serve as a proxy for open-system behavior for Re- Os. As a result, LA-ICP-MS/MS Re- Os analysis can serve both as a stand-alone geochronological tool and as an efficient screening method prior to conventional ID-N-TIMS, helping to identify optimal intervals and exclude isotopically disturbed material. Together, our study demonstrates that in-situ Re- Os geochronology of organic-rich shales is technically viable, geologically informative, and broadly applicable, opening new opportunities to investigate basin evolution, metallogenesis, hydrocarbon systems, and Earth-system processes across deep time.

Chemical Geology↗

USGS2026

Trace element heterogeneity and crystallization history of the Plesovice zircon: Implications for its use as a U–Pb LA-ICP-MS reference material

Zircon crystals from Plešovice hyperpotassic granulite (HPG) have been widely used as a reference material for LA-ICP-MS dating. Detailed cathodoluminescence (CL) imaging and trace element analysis reveal a complex internal structure of Plešovice zircon linked to extreme chemical heterogeneity, which allows us to distinguish different zircon domains formed during its crystallization: (i) rare low-CL cores enriched in U, Nb, HREE and Y; (ii) dominant sector-zoned to oscillatory-zoned domains, and (iii) CL-bright rims poor in trace elements. Relic fine oscillatory zoned areas are chemically homogeneous, whereas coarsened and blurred areas, and CL-dark replacement domains, are heterogeneous. Based on these data we suggest a complex and protracted zircon evolution: (i) crystallization of metamorphic zircon in anatectic calc-alkaline granulite; (ii) magmatic zircon crystallization at high temperature and pressure in a dry ultrapotassic melt at presence of peritectic garnet; (iii) coupled zircon dissolution-precipitation processes triggered by percolating hydrous residual melt; and (iv) coarsening and replacement of the pre-existing zircon due to prolonged exposure to a reactive fluid/hydrous melt. New CA-ID-TIMS U Pb dates between 337.167 ± 0.080 and 337.840 ± 0.080 Ma confirm crystallization age for HPG zircon at around 337.4 Ma and suggest that previously published dates of 336.37 Ma were biased by non-mitigated lead loss. We thus confirm the U/Pb homogeneity of Plešovice reference zircon despite its chemical heterogeneity. We further discuss the implications of using the chemically extremely heterogeneous Plešovice reference zircon as primary or secondary standard for in-situ LA-ICP-MS geochronology, in particular for quantification of the chemical matrix-dependence of the relative sensitivity factor ( β ) of laser ablation.

Plešovice quarry↗

USGS2007

Cleats and their relation to geologic lineaments and coalbed methane potential in Pennsylvanian coals in Indiana

Cleats and fractures in Pennsylvanian coals in southwestern Indiana were described, statistically analyzed, and subsequently interpreted in terms of their origin, relation to geologic lineaments, and significance for coal permeability and coalbed gas generation and storage. These cleats can be interpreted as the result of superimposed endogenic and exogenic processes. Endogenic processes are associated with coalification (i.e., matrix dehydration and shrinkage), while exogenic processes are mainly associated with larger-scale phenomena, such as tectonic stress. At least two distinct generations of cleats were identified on the basis of field reconnaissance and microscopic study: a first generation of cleats that developed early on during coalification and a second generation that cuts through the previous one at an angle that mimics the orientation of the present-day stress field. The observed parallelism between early-formed cleats and mapped lineaments suggests a well-established tectonic control during early cleat formation. Authigenic minerals filling early cleats represent the vestiges of once open hydrologic regimes. The second generation of cleats is characterized by less prominent features (i.e., smaller apertures) with a much less pronounced occurrence of authigenic mineralization. Our findings suggest a multistage development of cleats that resulted from tectonic stress regimes that changed orientation during coalification and basin evolution. The coals studied are characterized by a macrocleat distribution similar to that of well-developed coalbed methane basins (e.g., Black Warrior Basin, Alabama). Scatter plots and regression analyses of meso- and microcleats reveal a power-law distribution between spacing and cleat aperture. The same distribution was observed for fractures at microscopic scale. Our observations suggest that microcleats enhance permeability by providing additional paths for migration of gas out of the coal matrix, in addition to providing access for methanogenic bacteria. The abundance, distribution, and orientation of cleats control coal fabric and are crucial features in all stages of coalbed gas operations (i.e., exploration and production). Understanding coal fabric is important for coal gas exploration as it may be related to groundwater migration and the occurrence of methanogenic bacteria, prerequisite to biogenic gas accumulations. Likewise, the distribution of cleats in coal also determines pathways for migration and accumulation of thermogenic gas generated during coalification. ?? 2007 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2008

Progression in sulfur isotopic compositions from coal to fly ash: Examples from single-source combustion in Indiana

Sulfur occurs in multiple mineral forms in coals, and its fate in coal combustion is still not well understood. The sulfur isotopic composition of coal from two coal mines in Indiana and fly ash from two power plants that use these coals were studied using geological and geochemical methods. The two coal beds are Middle Pennsylvanian in age; one seam is the low-sulfur (< 1%) Danville Coal Member of the Dugger Formation and the other is the high-sulfur (> 5%) Springfield Coal Member of the Petersburg Formation. Both seams have ash contents of approximately 11%. Fly-ash samples were collected at various points in the ash-collection system in the two plants. The results show notable difference in ??34S for sulfur species within and between the low-sulfur and high-sulfur coal. The ??34S values for all sulfur species are exclusively positive in the low-sulfur Danville coal, whereas the ??34S values for sulfate, pyritic, and organic sulfur are both positive and negative in the high-sulfur Springfield coal. Each coal exhibits a distinct pattern of stratigraphic variation in sulfur isotopic composition. Overall, the ??34S for sulfur species values increase up the section in the low-sulfur Danville coal, whereas they show a decrease up the vertical section in the high-sulfur Springfield coal. Based on the evolution of ??34S for sulfur species, it is suggested that there was influence of seawater on peat swamp, with two marine incursions occurring during peat accumulation of the high-sulfur Springfield coal. Therefore, bacterial sulfate reduction played a key role in converting sulfate into hydrogen sulfide, sulfide minerals, and elemental sulfur. The differences in ??34S between sulfate sulfur and pyritic sulfur is very small between individual benches of both coals, implying that some oxidation occurred during deposition or postdeposition. The ??34S values for fly ash from the high-sulfur Springfield coal (averaging 9.7???) are greatly enriched in 34S relative to those in the parent coal (averaging 2.2???). This indicates a fractionation of sulfur isotopes during high-sulfur coal combustion. By contrast, the ??34S values for fly-ash samples from the low-sulfur Danville coal average 10.2???, only slightly enriched in 34S relative to those from the parent coal (average 7.5???). The ??34S values for bulk S determined directly from the fly-ash samples show close correspondence with the ??34S values for SO4- 2 leached from the fly ash in the low-sulfur coal, suggesting that the transition from pyrite to sulfate occurred via high-temperature oxidation during coal combustion. ?? 2007 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2008

Methanogenic pathways of coal-bed gas in the Powder River Basin, United States: The geologic factor

Coal-bed gas of the Tertiary Fort Union and Wasatch Formations in the Powder River Basin in Wyoming and Montana, U.S. was interpreted as microbial in origin by previous studies based on limited data on the gas and water composition and isotopes associated with the coal beds. To fully evaluate the microbial origin of the gas and mechanisms of methane generation, additional data for 165 gas and water samples from 7 different coal-bed methane-bearing coal-bed reservoirs were collected basinwide and correlated to the coal geology and stratigraphy. The C1/(C2 + C3) ratio and vitrinite reflectance of coal and organic shale permitted differentiation between microbial gas and transitional thermogenic gas in the central part of the basin. Analyses of methane ??13C and ??D, carbon dioxide ??13C, and water ??D values indicate gas was generated primarily from microbial CO2 reduction, but with significant gas generated by microbial methyl-type fermentation (aceticlastic) in some areas of the basin. Microbial CO2 reduction occurs basinwide, but is generally dominant in Paleocene Fort Union Formation coals in the central part of the basin, whereas microbial methyl-type fermentation is common along the northwest and east margins. Isotopically light methane ??13C is distributed along the basin margins where ??D is also depleted, indicating that both CO2-reduction and methyl-type fermentation pathways played major roles in gas generation, but gas from the latter pathway overprinted gas from the former pathway. More specifically, along the northwest basin margin gas generation by methyl-type fermentation may have been stimulated by late-stage infiltration of groundwater recharge from clinker areas, which flowed through highly fractured and faulted coal aquifers. Also, groundwater recharge controlled a change in gas composition in the shallow Eocene Wasatch Formation with the increase of nitrogen and decrease of methane composition of the coal-bed gas. Other geologic factors, such as burial, thermal and maturation history, lateral and vertical continuity, and coalification of the coal beds, also played a significant role in controlling methanogenic pathways and provided new perspectives on gas evolution and emplacement. The early-stage gas produced by CO2 reduction has mixed with transitional thermogenic gas in the deeper, central parts of the Powder River Basin to form 'old' gas, whereas along the basin margins the overprint of gas from methyl-type fermentation represents 'new' gas. Thus, a clear understanding of these geologic factors is necessary to relate the microbiological, biogeochemical, and hydrological processes involved in the generation of coal-bed gas.

International Journal of Coal Geology↗

USGS2009

Compression-cuticle relationship of seed ferns: Insights from liquid-solid states FTIR (Late Palaeozoic-Early Mesozoic, Canada-Spain-Argentina)

Cuticles have been macerated from suitably preserved compressed fossil foliage by Schulze's process for the past 150 years, whereas the physical-biochemical relationship between the "coalified layer" with preserved cuticle as a unit has hardly been investigated, although they provide complementary information. This relationship is conceptualized by an analogue model of the anatomy of an extant leaf: "vitrinite (mesophyll) + cuticle (biomacropolymer) = compression". Alkaline solutions from Schulze's process as a proxy for the vitrinite, are studied by means of liquid-solid states Fourier transform infrared spectroscopy (FTIR). In addition, cuticle-free coalified layers and fossilized cuticles of seed ferns mainly from Canada, Spain and Argentina of Late Pennsylvanian-Late Triassic age are included in the study sample. Infrared data of cuticle and alkaline solutions differ which is primarily contingent on the mesophyll +biomacropolymer characteristics. The compression records two pathways of organic matter transformation. One is the vitrinized component that reflects the diagenetic-post-diagenetic coalification history parallel with the evolution of the associated coal seam. The other is the cuticle that reflects the sum-total of evolutionary pathway of the biomacropolymer, its monomeric, or polymeric fragmentation, though factors promoting preservation include entombing clay minerals and lower pH conditions. Caution is advised when interpreting liquid-state-based FTIR data, as some IR signals may have resulted from the interaction of Schulze's process with the cuticular biochemistry. A biochemical-study course for taphonomy is suggested, as fossilized cuticles, cuticle-free coalified layers, and compressions are responses to shared physicogeochemical factors. ?? 2009 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗