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    Improved On-line Measurement of Bone Collagen D/H as Forensic Environmental Indicator
    (Isoscapes 2008 Conference, 2008-04-07) Topalov, Katarina; Schimmelmann, Arndt; Polly, David; Sauer, Peter E.
    The organic hydrogen isotope ratio (deuterium/hydrogen or D/H) in the tissues of terrestrial organisms is related to D/H values of precursor hydrogen in diet and water from precipitation. D/H in (fossil) bone collagen potentially characterizes the (paleo)environment of an animal. However, the original (paleo)environmental isotopic signal of organic hydrogen is largely limited to carbon-linked hydrogen (C-H). In contrast, organic hydrogen that is chemically linked to other elements (e.g., oxygen O-H and nitrogen N-H) is more loosely bound and exchanges with ambient water, even during storage and sample preparation. Further, the fraction of exchangeable hydrogen in total hydrogen can vary among samples. The uncertainty from exchangeable hydrogen can be reduced via equilibration with isotopically known water vapors and subsequent mass-balance calculations arriving at the D/H of non-exchangeable hydrogen in collagen. Labor-intensive methods for isotopic equilibration of exchangeable organic hydrogen with water vapor have been used for more than 15 years. Here we present data from steam-equilibrated samples using a more efficient continuous-flow (i.e., on-line) approach using a ThermoFinnigan TC/EA fitted with an autosampler. Collagens from bones of modern White tail deer (Odocoileus virginianus) and Southern mule deer (O. hemionus) across climate gradients in the USA were prepared for our preliminary study. Traditionally, TC/EA samples are wrapped tightly in non-permeable silver capsules that limit the access of steam to collagen. Our samples were loaded into individual micro-perforated silver TC/EA cups. Cups were crimped shut and looked like small shopping bags. The perforations at the bottom of each cup were small enough that collagen could not spill out of the cup, but steam and gas could freely pass into and out of the cups. Steam equilibration of an entire carousel (up to 49 cups) in an equilibration chamber occurred overnight with isotopically known steam at 115ºC, followed by drying with dry nitrogen, cooling, rapid transfer of the carousel to the TC/EA, and determination of D/H. We present preliminary results from collagens and discuss advantages of the new method.
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    High resolution study of pyrite framboid distribution in varved Santa Barbara Basin sediments and implications for water-column oxygenation
    (2007-05) Schieber, Juergen; Schimmelmann, Arndt
    Monitoring of the concentration of dissolved elemental oxygen (i.e., ‘oxygenation’) of sub-sill waters in the Santa Barbara Basin (SBB) over the last few decades has consistently demonstrated sub-oxic bottom water conditions. However, anoxic conditions and hydrogen sulfide (H2S) are present below a few millimeters depth in the sedimentary column. The absence of euxinic conditions (i.e., anoxic-sulfidic: no free O2 but free H2S) in any part of the modern SBB water column makes this basin geochemically distinct from the Black Sea and other more oxygen-depleted basins. The varved sediment record from the central SBB has been used extensively for high-resolution paleoceanographic reconstructions. The SBB and other oxygen-depleted basins are considered modern analogs for black shales. Geochemical proxies for paleo-redox conditions in black shales need to be tested against modern, well-constrained depositional systems like the SBB. Pyrite framboids are a common component in many anoxic marine sediments and are deemed to carry paleoceanographic information. Observations from modern Black Sea sediment yielded the hypotheses that (i) abundant small framboids below 5 m diameter indicate euxinic (anoxic-sulfidic) bottom waters, and (ii) mean framboid sizes above 5m indicate suboxic or normally oxygenated bottom waters. We are using Scanning Electron Microscopy to compile a detailed inventory of framboid occurrence in AD 1983-2004 SBB varves and compare framboid size distribution against the known history of SBB water column oxygenation. Our ground-truthing effort has shown that framboids in modern SBB sediment dominantly are in the 2-4 m range and thus show closely similar size distributions to those measured in Black Sea sediments underlying an euxinic water column. Of course, the lower SBB water column is suboxic, and therefore we conclude that the framboid size distribution in modern sediment and in black shales has no diagnostic value for paleo-water column oxygenation. Our data further indicate significant variability in mean framboid size between successive varves that do not correlate with historic changes in SBB water oxygenation. We are evaluating other potential factors that could affect framboid size, for example (i) the availability of iron from clastic terrestrial input from the continent, (ii) the availability of freshly deposited organic matter nourishing the microbial community and influencing the redox profile near the sediment/water interface, and (iii) the depth of burial within the near-surface sediment that fosters the precipitation of framboids. The generally lower abundance of framboids in the youngest, uppermost varves suggests that it takes several years of mineralization before framboid formation goes to completion in a given sediment layer. After about 5 years framboid abundance appears to stabilize, providing further support to the view that framboids do not form in the water column and should not be considered recorders of water column oxygenation.
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    Compound Specific Carbon and Hydrogen Stable Isotope Ratios of Coalbed Gases in Southeastern Illinois Basin
    (2007-01-12) Strapoc, Dariusz; Schimmelmann, Arndt; Mastalerz, Maria; Eble, Corland
    Coalbed gases and waters from exploratory and production gas wells in the southeastern Illinois Basin were sampled to geochemically assess the origin of coalbed gases, with emphasis on Springfield and Seelyville coal members that are commercially targeted for coalbed methane production. On-line analyses of hydrocarbon gases (methane to butanes: C1, C2, C3, n-C4, i-C4) and CO2 yielded chemical concentrations, Delta-D, and Delta 13C values. The low thermal maturity of Indiana coals (vitrinite reflectance Ro ~ 0.6%) is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gas that has greater than or equal to 96% methane generated via bacterial CO2-reduction. In contrast, thermogenic coalbed gas was generated by the stratigraphically equivalent coalbeds in western Kentucky’s Rough Creek Graben zone where higher maturities of up to Ro ~ 0.8% are reached due to tectonic and hydrothermal activity. No secondary biogenic methane was observed in Kentucky coalbed gases, probably due to greater burial depths and limited recharge of meteoric water. The two differently sourced types of coalbed gases are compositionally and isotopically distinct. Microbial biodegradation of thermogenic C2+ hydrocarbon gases in Indiana coalbeds preferentially targets C3 and introduces isotope fractionation whereby remaining C3 is enriched in heavy hydrogen and carbon isotopes.