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We describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river-water/seawater mixing zone of the Colorado River estuary. Sclerochronological techniques are used to identify tidally-induced, fortnight-scale bundles of daily growth increments within shell cross-sections. These fortnightly markers are used to establish a chronology for samples taken for δ18O analysis. A composite seasonal δ18O profile derived from five shells that grew in the absence of river-water flow is used as a baseline against which profiles of river-influenced shells are compared. Because this comparison is between matched fortnights within a year, the temperature...
The Fruitland Formation of the San Juan Basin was deposited during the late Cretaceous and is associated with significant reservoirs of coalbed methane (CBM). The purpose of this study is to determine the origin and history of waters associated with the formation, using long-lived cosmogenic and stable isotope systems. Ratios of 129I/I and stable isotope values (?D and ?18O) were determined in waters from close to 100 wells, 36Cl/Cl ratios for a subset of these samples. A significant group of samples has 129I/I ratios between 100 � 10?15 and 200 � 10?15, indicating minimum iodine ages close to 60 Ma. If these ages are corrected for the addition of fissiogenic 129I, they are compatible with the depositional age of...
Several potential dust sources, including generic sources of sparsely vegetated alluvium, playa deposits, and anthropogenic emissions, as well as the area around Owens Lake, California, affect the composition of modern dust in the southwestern United States. A comparison of geochemical analyses of modern and old (a few thousand years) dust with samples of potential local sources suggests that dusts reflect four primary sources: (1) alluvial sediments (represented by Hf, K, Rb, Zr, and rare-earth elements, (2) playas, most of which produce calcareous dust (Sr, associated with Ca), (3) the area of Owens (dry) Lake, a human-induced playa (As, Ba, Li, Pb, Sb, and Sr), and (4) anthropogenic and/or volcanic emissions...
Using isotopic ratios of Sr, C and O, we trace calcium carbonate through surface systems across a wide region of semi-arid terrain in Arizona, southwestern USA, in order to evaluate the contribution of cations from silicate weathering to soil carbonate. We present 87Sr/86Sr ratios of soil carbonate, parent rock, dry river course silts, floodplain, playa, dust and rain samples, as well as ?18O and ?13C values of selected samples. Results show that both parent rock and dust are important sources of cations for soil carbonate in this inland setting where bedrock is dominated by silicate lithologies. Dust in southeast Arizona has higher 87Sr/86Sr ratios (0.7100?0.7123) than Phanerozoic sea water (0.7070?0.7096). These...
The C28 sterane was identified and the presence of the C27 and C29 steranes in Green River oil shale was confirmed. This was accomplished by comparison of the spectra of the isolated components with authentic standards. Published in Geochimica et Cosmochimica Acta, volume 33, issue 10, on pages 1304 - 1307, in 1969.
The potential to reconstruct paleoclimate from analyses of stable isotopes in fossil leaf cellulose could be enhanced by adequate calibration. This potential is likely to be particularly great in mid-latitude deserts, where a rich store of fossil leaves is available from rodent middens. Trends in δD and δ18O of leaf cellulose were examined for three species growing across climatic gradients caused by elevation and slope aspect in southeastern Utah, USA. The species differed in morphology (Pinus edulis vs. Yucca glauca), photosynthetic pathway (C3Y. glauca vs. CAM Yucca baccata) or both (P. edulis vs. Y. baccata). The δDLCN (leaf cellulose nitrate) and δ18OLC (leaf cellulose) values of P. edulis decreased with...
The sulfur geochemistry of the lacustrine Paleogene Green River Formation (Colorado, Utah, and Wyoming, USA) is unlike that of most marine and other lacustrine rocks. Distinctive chemical, isotopic, and mineralogical characteristics of the formation are pyrrhotite and marcasite, high contents of iron mineral sulfides strikingly enriched in34S, cyclical trends in sulfur abundance and δ34S values, and long-term evolutionary trends in δ34S values. Analyses that identified and quantified these characteristics include carbonate-free abundance of organic carbon (0.13–47 wt%), total iron (0.31–13 wt%), reactive iron (>70% of total iron), total sulfur (0.02–16 wt%), acid-volatile monosulfide (SAv), disulfide (SDi...
Fifty-two cyclic alkanes, isolated from the bitumen of Green River Shale, were analyzed by mass spectrometry. The molecular formula of each cycloalkane was determined and, where possible, structural assignments were proposed for the alkanes on the basis of principal fragment ions and similarities in spectra to products of known configuration. Structural resemblance of these cycloalkanes to the hydrocarbon framework of biologically derived isoprenoid lipids was noted. Twenty-one cycloalkanes displayed fragmentation patterns similar to tetraalkyl substituted cyclohexanes. These compounds probably had their origin in carotenoid pigments. Six additional cyclic hydrocarbons produced mass spectra resembling the spectra...
The San Juan Basin natural gas field, located in northwestern New Mexico and southwestern Colorado in the USA, is a case-type coalbed methane system. Groundwater is thought to play a key role in both biogenic methane generation and the CO2 sequestration potential of coalbed systems. We show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas. We collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control. Stable isotope and major species determination clearly characterize the gas in the...
Zinc and Cu play important roles in the biogeochemistry of natural systems, and it is likely that these interactions result in mass-dependent fractionations of their stable isotopes. In this study, we examine the relative abundances of dissolved Zn and Cu isotopes in a variety of stream waters draining six historical mining districts located in the United States and Europe. Our goals were to (1) determine whether streams from different geologic settings have unique or similar Zn and Cu isotopic signatures and (2) to determine whether Zn and Cu isotopic signatures change in response to changes in dissolved metal concentrations over well-defined diel (24-h) cycles. Average δ66Zn and δ65Cu values for streams varied...
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