Geology topics
Publications and source records attributed to Stephen A. Wilson.
The ShBOQ-1 geochemical reference material is relevant to studies of the organic geochemistry and mineralogy of petroleum source rocks containing high concentrations of carbonate minerals and organic sulfur-rich, oil-prone marine organic matter. ShBOQ-1 is geochemically and mineralogically similar to the lower part of the Upper Cretaceous Eagle Ford Shale.
The expansion of unconventional petroleum resource exploration and production in the United States has led to an increase in source rock characterization efforts, particularly related to bulk organic and mineralogical properties. To support the analytical and research needs of industry and academia, as well as internal work, the U.S. Geological Survey (USGS) has collected and prepared shale geochemical reference materials (GRMs) from several major shale petroleum systems in the U.S. The sources of these materials are the Late Cretaceous Boquillas (lower Eagle Ford-equivalent) Formation (roadcut near Del Rio, TX), Late Cretaceous Mancos Shale (outcrop near Delta, CO), Devonian–Mississippian Woodford Shale (outcrop near Ardmore, OK), Late Cretaceous Niobrara Formation (quarry near Lyons, CO), Middle Devonian Marcellus Shale (creek bed in LeRoy, NY), and Eocene Mahogany zone oil shale of the Green River Formation (oil shale mine near Rifle, CO). Of particular interest in the development of these GRMs has been the examination of variability between laboratories and specific methods or instruments in commonly made measurements, including major- and trace-element concentrations, X-ray diffraction (XRD) mineralogy, total organic carbon (TOC) content, and programmed pyrolysis (PP) parameters. For the component concentrations and parameters we measured, the techniques and instrument types included: (1) elemental analysis by X-ray fluorescence, inductively coupled plasma mass spectrometry, and instrumental neutron activation analysis; (2) XRD mineralogy with various preparatory methods (spray drying or micronizing with or without internal standard); (3) TOC by combustion with infrared detection after carbonate removal or the PP approach; (4) PP by Rock-Eval 2 or more recently developed instruments (Rock-Eval 6, Source Rock Analyzer or SRA, and Hydrocarbon Analyzer With Kinetics or HAWK). Overall, the results showed that the selected shales cover a wide range of source rock organic and mineralogical properties. Major- and trace-element chemistry results showed low heterogeneity consistent with other USGS GRMs. Comparison of TOC results showed coefficients of variation (COV) of around 5% and the most consistent organic geochemical results between different laboratories and methods. Arguably the most relevant PP measurement, S2 or kerogen hydrocarbon-generating potential (mg-HC/g-rock), showed a somewhat wider range of variability than TOC (COV ~10%), but was consistent between the three modern instruments and the industry-standard Rock-Eval 2. Major phase mineralogy (mineral concentrations ≥10 wt. %, organic-free basis) were comparable between laboratories, but variability in minor phase identification and quantification was observed. Utilization of these shale GRMs as quality control samples and testing materials is expected to help support analytical and experimental efforts in the continued development of unconventional petroleum resources.
Raman spectroscopy has recently received attention as a means to estimate thermal maturity of organic matter in petroleum generating source rocks to complement more traditional approaches such as vitrinite reflectance and programmed pyrolysis. While many studies have observed positive correlations between source rock thermal maturity and Raman spectral parameters, little attention has been given to the degree of variation in the Raman response across individual organic grains, especially for shales or mudrocks with highly dispersed organic matter. Here the spatial variation in Raman estimates of thermal maturity within individual organic grains is assessed from shales from the Boquillas, Marcellus, Niobrara, and Woodford Formations. The thermal maturity parameters extracted from Raman spectra can vary widely across distances of ≤5 μm within the same organic grain. These results illustrate the high degree of chemical heterogeneity inherent to the organic matter within these source rocks. Additionally, the spatial pattern of the Raman parameters, as revealed by 2D Raman mapping, imply that organic matter structure is influenced by associations with mineral surfaces within the surrounding rock matrix. Chemical heterogeneity and matrix effects directly impact the Raman response from these types of materials and thus the extracted thermal maturity estimate. These findings highlight the care which must be adopted when making Raman measurements of organic matter within source rock matrices, especially for samples which feature highly dispersed, heterogeneous organic matter as found in petroliferous mudrocks.
The U.S. Environmental Protection Agency (USEPA) began work in Libby, Mont. in 1999 when an Emergency Response Team was sent to investigate local concern and media reports regarding asbestos-contaminated vermiculite. Since that time, the site has been granted Superfund status and site remediation to a safe level of asbestos has been ongoing. The amphibole asbestos from the Vermiculite Mountain vermiculite deposit near Libby, Mont. (Libby amphibole) is unusual in the sense that it is currently not classified as one of the regulated six asbestos minerals—chrysotile (a serpentine mineral) and the amphibole minerals amosite (asbestiform cummingtonite-grunerite), crocidolite (asbestiform riebeckite), asbestiform anthophyllite, asbestiform tremolite, and asbestiform actinolite. The amphiboles from the Vermiculite Mountain vermiculite deposit, primarily winchite and richterite, are related to tremolite and in the past have been referred to as sodium-rich tremolite or soda tremolite (Larsen, 1942; Boettcher, 1966; Wylie and Verkouteren, 2000; Gunter and others, 2003; Meeker and others, 2003). The public health issues in Libby, Mont. have brought to light many of the inconsistencies in the literature regarding fiber characteristics, nomenclature, and toxicology. To better understand the toxicological characteristics of the Libby amphibole, investigators require a sufficient quantity of material representing the range of fibrous amphiboles present in the vicinity of Vermiculite Mountain to use in toxicology studies. The material collected in 2000 (Meeker and others, 2003) has been exhausted and a second collection and preparation effort, funded by the USEPA, was conducted in 2007. Both the 2000 (LA2000) and 2007 (LA2007) materials were generated to support research needs identified by the USEPA and the National Toxicology Program, and new in-vivo and in-vitro toxicology studies are underway. This Open-File Report describes the process of preparation and summarizes the chemistry and mineralogy of the LA2007 toxicological testing material.
One of the difficulties in performing speciation analyses on solid samples is finding a suitable extraction method. Traditional methods for extraction of hexavalent chromium, Cr(VI), in soils, such as SW846 Method 3060A, can be tedious and are not always compatible with some determination methods. For example, the phosphate and high levels of carbonate and magnesium present in the U.S. Environmental Protection Agency (USEPA) Method 3060A digestion for Cr(VI) were found to be incompatible with the High Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry (HPLC-ICP-MS) detection method used by our laboratory. Modification of Method 3060A by eliminating the use of the phosphate buffer provided improved performance with the detection method, however dilutions are still necessary to achieve good chromatographic separation and detection of Cr(VI). An ultrasonic extraction method using a 1 mM Na2CO3 - 9 mM NaHCO3 buffer solution, adapted from Occupational Safety and Health Administration (OSHA) Method ID215, has been used with good results for the determination of Cr(VI) in air filters. The average recovery obtained for BCR-545 - Welding Dust Loaded on Filter (IRMM, Belgium) using this method was 99 percent (1.2 percent relative standard deviation) with no conversion of Cr(VI) to Cr(III) during the extraction process. This ultrasonic method has the potential for use with other sample matrices, such as ashes and soils. Preliminary investigations using NIST 2701 (Hexavalent Chromium in Contaminated Soil) loaded onto quartz filters showed promising results with approximately 90 percent recovery of the certified Cr(VI) value. Additional testing has been done using NIST 2701 and NIST 2700 using different presentation methods. Extraction efficiency of bulk presentation, where small portions of the sample are added to the bottom of the extraction vessel, will be compared with supported presentation, where small portions of the sample are loaded onto a quartz filter prior to extraction. In addition, results obtained from the standard grinding preparation of NIST 2701 and NIST 2700 will be compared with micronizing to reduce particle size before extraction.
Reference materials (RM) are required for quantitative analyses and their successful use is associated with the degree of homogeneity, and the traceability and confidence limits of the values established by characterisation. During the production of a RM, the chemical characterisation can only commence after it has been demonstrated that the material has the required level of homogeneity. Here we describe the preparation of BRP-1, a proposed geochemical reference material, and the results of the tests to evaluate its degree of homogeneity between and within bottles. BRP-1 is the first of two geochemical RM being produced by Brazilian institutions in collaboration with the United States Geological Survey (USGS) and the International Association of Geoanalysts (IAG). Two test portions of twenty bottles of BRP-1 were analysed by wavelength dispersive-XRF spectrometry and major, minor and eighteen trace elements were determined. The results show that for most of the investigated elements, the units of BRP-1 were homogeneous at conditions approximately three times more rigorous than those strived for by the test of “sufficient homogeneity”. Furthermore, the within bottle homogeneity of BRP-1 was evaluated using small beam (1 mm 2 ) synchrotron radiation XRF spectrometry and, for comparison, the USGS reference materials BCR-2 and GSP-2 were also evaluated. From our data, it has been possible to assign representative minimum masses for some major constituents (1 mg) and for some trace elements (1-13 mg), except Zr in GSP-2, for which test portions of 74 mg are recommended.
Every year in the United States, millions of measurements are made on the chemical composition of items that affect us on a daily basis. The accuracy of these measurements is routinely determined by the analysis of appropriate reference materials. In the field of earth science, reference materials are particularly important because they help us develop a better understanding of the processes that have shaped, and continue to shape the world around us. USGS reference materials are distributed internationally to organizations involved in geochemical and environmental analysis, instrumentation and methods development, and industrial research and quality assurance. Reference materials are widely used in the development and validation of geochemical models used by the USGS.
New glass reference materials GSA-1G, GSC-1G, GSD-1G and GSE-1G have been characterised using a prototype solid state laser ablation system capable of producing wavelengths of 193 nm, 213 nm and 266 nm. This system allowed comparison of the effects of different laser wavelengths under nearly identical ablation and ICP operating conditions. The wavelengths 213 nm and 266 nm were also used at higher energy densities to evaluate the influence of energy density on quantitative analysis. In addition, the glass reference materials were analysed using commercially available 266 nm Nd:YAG and 193 nm ArF excimer lasers. Laser ablation analysis was carried out using both single spot and scanning mode ablation. Using laser ablation ICP-MS, concentrations of fifty-eight elements were determined with external calibration to the NIST SRM 610 glass reference material. Instead of applying the more common internal standardisation procedure, the total concentration of all element oxide concentrations was normalised to 100%. Major element concentrations were compared with those determined by electron microprobe. In addition to NIST SRM 610 for external calibration, USGS BCR-2G was used as a more closely matrix-matched reference material in order to compare the effect of matrix-matched and non matrix-matched calibration on quantitative analysis. The results show that the various laser wavelengths and energy densities applied produced similar results, with the exception of scanning mode ablation at 266 nm without matrix-matched calibration where deviations up to 60% from the average were found. However, results acquired using a scanning mode with a matrix-matched calibration agreed with results obtained by spot analysis. The increased abundance of large particles produced when using a scanning ablation mode with NIST SRM 610, is responsible for elemental fractionation effects caused by incomplete vaporisation of large particles in the ICP.
In 1996, the U.S. Geological Survey conducted a reconnaissance baseline geochemical study in central Idaho. The purpose of the baseline study was to establish a 'geochemical snapshot' of the area, as a datum for monitoring future change in the geochemical landscape, whether natural or human-induced. This report presents the methology, analytical results, and sample descriptions for water, sediment, and heavy-mineral concentrate samples collected during this geochemical investigation. In the summer of 2000, the Clear Creek, Little Pistol, and Shellrock wildfires swept across much of the area that was sampled. Thus, these data represent a pre-fire baseline geochemical dataset. A 2001 post- fire study is planned and will involve re-sampling of the pre-fire baseline sites, to allow for pre- and post-fire comparison.
Samples of silicate rocks are prepared by sodium carbonate fusion and then treated by ion chromatography. The method was tested for geological standards with chloride concentration between 0.003 and 3%. Observed chloride concentrations comparedd favorably with literature values. The relative standard deviation and detection limit for the method were 8% and 7 ppm, respectively. Up to 30 determination per 24-hour period were possible. ?? 1983.