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Carbon 14 from Lead Nitrate

Description: Report describing the production of carbon 14 from Pb(NO3)2 in the Oak Ridge Nuclear Reactor via the reaction N14 (n.p.) C14.
Date: 1949
Creator: Goodman, Martin R. & Longacre, Andrew, 1904-
Partner: UNT Libraries Government Documents Department

Summary of Conference on the Toxicity of Carbon 14 Held at Argonne National Laboratory, January 15-16, 1952

Description: Report issued by the Argonne National Laboratory discussing the Conference on the Toxicity of Carbon 14. At the outset of the meeting it was emphasized that the group was brought together to discuss work which had a bearing on the toxicity of C14 compounds used either clinically or industrially, and the hope was expressed that the group might be able to reach some conclusions on these matters. This report includes tables.
Date: March 1952
Creator: Brues, A. M. & Buchanan, D. L.
Partner: UNT Libraries Government Documents Department

Young organic matter as a source of carbon dioxide outgassing from Amazonian rivers

Description: Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon, but little agreement exists about the sources or turnover times of this carbon. Here we present results of an extensive survey of the carbon isotope composition ({sup 13}C and {sup 14}C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system. We find that respiration of contemporary organic matter (less than 5 years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in mid-size to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age. We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics.
Date: June 23, 2005
Creator: Mayorga, E; Aufdenkampe, A K; Masiello, C A; Krusche, A V; Hedges, J I; Quay, P D et al.
Partner: UNT Libraries Government Documents Department

Lifetime Measurement of the 2{sup +}{sub 1} state in {sup 20}C

Description: Establishing how and when large N/Z values require modified or new theoretical tools is a major quest in nuclear physics. Here we report the first measurement of the lifetime of the 2{sup +}{sub 1} state in the near-dripline nucleus {sup 20}C. The deduced value of {tau}{sub #28;2{sup +}{sub 1}} = 9.8 ± 2.8(stat){sup +0.5}{sub −1.1}(syst) ps gives a reduced transition probability of B(E2;2{sup +}{sub 1}{yields}0{sup +}{sub g.s.}) = 7.5{sup +3.0}{sub −1.7}(stat){sup +1.0}{sub −0.4}(syst) e{sup 2}fm{sup 4} in good agreement with a shell model calculation using isospin-dependent effective charges.
Date: June 28, 2011
Creator: Petri, Marina-Kalliopi; Fallon, Paul; Macchiavelli, Augusto; Paschalis, Stephanos; Starosta, Krzysztof; Baugher, Travis et al.
Partner: UNT Libraries Government Documents Department

Carbon Isotopic Studies of Assimilated and Ecosystem Respired CO2 in a Southeastern Pine Forest

Description: Carbon dioxide is the major “greenhouse” gas responsible for global warming. Southeastern pine forests appear to be among the largest terrestrial sinks of carbon dioxide in the US. This collaborative study specifically addressed the isotopic signatures of the large fluxes of carbon taken up by photosynthesis and given off by respiration in this ecosystem. By measuring these isotopic signatures at the ecosystem level, we have provided data that will help to more accurately quantify the magnitude of carbon fluxes on the regional scale and how these fluxes vary in response to climatic parameters such as rainfall and air temperature. The focus of the MBL subcontract was to evaluate how processes operating at the physiological and ecosystem scales affects the resultant isotopic signature of plant waxes that are emitted as aerosols into the convective boundary layer. These wax aerosols provide a large-spatial scale integrative signal of isotopic discrimination of atmospheric carbon dioxide by terrestrial photosynthesis (Conte and Weber 2002). The ecosystem studies have greatly expanded of knowledge of wax biosynthetic controls on their isootpic signature The wax aerosol data products produced under this grant are directly applicable as input for global carbon modeling studies that use variations in the concentration and carbon isotopic composition of atmospheric carbon dioxide to quantify the magnitude and spatial and temporal patterns of carbon uptake on the global scale.
Date: April 10, 2008
Creator: Conte, Maureen H.
Partner: UNT Libraries Government Documents Department

The impact of biogenic carbon emissions on aerosol absorption inMexico City

Description: In order to determine the wavelength dependence of atmospheric aerosol absorption in the Mexico City area, the absorption angstrom exponents (AAEs) were calculated from aerosol absorption measurements at seven wavelengths obtained with a seven-channel aethalometer during two field campaigns, the Mexico City Metropolitan Area study in April 2003 (MCMA 2003) and the Megacity Initiative: Local and Global Research Observations in March 2006 (MILAGRO). The AAEs varied from 0.76 to 1.56 in 2003 and from 0.54 to 1.52 in 2006. The AAE values determined in the afternoon were consistently higher than the corresponding morning values, suggesting the photochemical formation of absorbing secondary organic aerosols (SOA) in the afternoon. The AAE values were compared to stable and radiocarbon isotopic measurements of aerosol samples collected at the same time to determine the sources of the aerosol carbon. The fraction of modern carbon (fM) in the aerosol samples, as determined from {sup 14}C analysis, showed that 70% of the carbonaceous aerosols in Mexico City were from modern sources, indicating a significant impact from biomass burning during both field campaigns. The {sup 13}C/{sup 12}C ratios of the aerosol samples illustrate the significant impact of Yucatan forest fires (C-3 plants) in 2003 and local grass fires (C-4 plants) at site T1 in 2006. A direct comparison of the fM values, stable carbon isotope ratios, and calculated aerosol AAEs suggested that the wavelength dependence of the aerosol absorption was controlled by the biogenically derived aerosol components.
Date: February 24, 2009
Creator: Marley, N; Gaffney, J; Tackett, M J; Sturchio, N; Hearty, L; Martinez, N et al.
Partner: UNT Libraries Government Documents Department

Experimental Geochemical Studies Relevant to Carbon Sequestration

Description: The authors are conducting laboratory studies to determine: (i) the thermophysical properties and phase relations of CO{sub 2}CH{sub 4}-H{sub 2}O fluids; (ii) the magnitude of stable isotope partitioning during calcite precipitation; and (iii) the utility of natural isotopic tracers in quantifying CO{sub 2} residence times, storage capacity and reaction mechanisms in the subsurface. The ultimate aim of the research on CO{sub 2}-CH{sub 4}H{sub 2}O fluids is to develop a comprehensive equation of state for binary and ternary mixtures of CO{sub 2}, CH{sub 4} and H{sub 2}O at pressure-temperature (P-T) conditions representative of those in deep gas fields and saline aquifers. To acquire the data needed to create the model, two unique, custom-designed devices at the Oak Ridge National Laboratory--a high pressure vibrating-tube densimeter, and a hydrogen-service internally heated pressure vessel--are being used to measure the densities, excess molar volumes, miscibility limits and activity-composition relations of CO{sub 2}H{sub 2}O, CH{sub 4}-H{sub 2}O and ternary CO{sub 2}-CH{sub 4}-H{sub 2}O mixtures at P-T conditions near the vapor-saturation phase boundary in the H{sub 2}O system. In another project, experiments are being conducted to determine the kinetics of carbonate precipitation from CO{sub 2}-rich saline waters, and associated isotope partitioning. Both inorganic and microbially mediated processes are being investigated under environmental conditions encountered during CO{sub 2} injection into the subsurface. Our results indicate that the behavior of isotopes, especially oxygen isotopes, is affected by the composition of water and the precipitation rate of carbonate minerals. We have also observed significant carbon isotope partitioning (4 to 8{per_thousand}) between CO{sub 2} and hydrocarbon-saturated rock (an EOR injection scenario) reacted statically at 25 C. These preliminary results suggest that a light isotopic component of CO{sub 2} may be retained in the reservoir, leading to isotopically heavier CO, further down the flow path.
Date: January 10, 2001
Creator: Blencoe, J. G.
Partner: UNT Libraries Government Documents Department

Using dissolved noble gas and isotopic tracers to evaluate the vulnerability of groundwater resources in a small, high elevation catchment to predicted climate changes

Description: We use noble gas concentrations and multiple isotopic tracers in groundwater and stream water in a small high elevation catchment to provide a snapshot of temperature, altitude, and physical processes at the time of recharge; and to determine subsurface residence times of different groundwater components. They identify three sources that contribute to groundwater flow: (1) seasonal groundwater recharge with short travel times, (2) water from bedrock aquifers that have elevated radiogenic {sup 4}He, and (3) upwelling of deep fluids that have 'mantle' helium and hydrothermal carbon isotope signatures. Although a bimodal distribution in apparent groundwater age indicates that groundwater storage times range from less than a year to several decades, water that recharges seasonally is the largest likely contributor to stream baseflow. Under climate change scnearios with earlier snowmelt, the groundwater that moves through the alluvial aquifer seasonally will be depleted earlier, providing less baseflow and possible extreme low flows in the creek during summer and fall. Dissolved noble gas measurements indciate recharge temperatures are 5 to 11 degrees higher than would be expected for direct influx of snowmelt, and that excess air concentrations are lower than would be expected for recharge through bedrock fractures. Instead, recharge likely occurs over diffuse vegetated areas, as indicated by {delta}{sup 13}C-DIC values that are consistent with incorporation of CO{sub 2} from soil respiration. Recharge temperatures are close to or slightly higher than mean annual air temperature, and are consistent with recharge during May and June, when snowpack melting occurs.
Date: October 2, 2009
Creator: Singleton, M J & Moran, J E
Partner: UNT Libraries Government Documents Department

Optimization of Direct Ionization of CO2 by Controlling the Gas Flow Inside of a Beam-Target

Description: We designed and optimized a target that directs a CO{sub 2} pulse onto a Ti surface where a Cs{sup +} sputtering beam ionizes the CO{sub 2} to generate C{sup -}. These targets will be used for the direct ionization of CO{sub 2} pulses to enable the measurement of carbon isotope ratios in real time. The design was based on the results of Comsol{trademark} simulations of the target configurations.
Date: March 7, 2011
Creator: Salazar Quintero, G A & Ognibene, T
Partner: UNT Libraries Government Documents Department

Middle to Late Holocene Fluctuations of C3 and C4 Vegetation in a Northern New England Salt Marsh, Sprague Marsh, Phippsburg Maine

Description: A 3.1 meter sediment core was analyzed for stable carbon isotope composition of organic matter and higher plant leaf wax (HPLW) lipid biomarkers to determine Holocene shifts in C{sub 3} (higher high marsh) and C{sub 4} (low and/or high marsh) plant deposition at the Sprague River Salt Marsh, Phippsburg, Maine. The carbon isotope composition of the bulk sediment and the HPLW parallel each other throughout most of the core, suggesting that terrestrial plants are an important source of organic matter to the sediments, and diagenetic alteration of the bulk sediments is minimal. The current salt marsh began to form 2500 cal yr BP. Low and/or high C{sub 4} marsh plants dominated deposition at 2000 cal yr BP, 700 cal yr BP, and for the last 200 cal yr BP. Expansion of higher high marsh C{sub 3} plants occurred at 1300 and 600 cal yr BP. These major vegetation shifts result from a combination of changes in relative sea-level rise and sediment accumulation rates. Average annual carbon sequestration rates for the last 2500 years approximate 40 g C yr{sup -1} m{sup -2}, and are in strong agreement with other values published for the Gulf of Maine. Given that Maine salt marshes cover an area of {approx}79 km{sup 2}, they represent an important component of the terrestrial carbon sink. More detailed isotopic and age records from a network of sediment cores at Sprague Marsh are needed to truly evaluate the long term changes in salt marsh plant communities and the impact of more recent human activity, including global warming, on salt marsh vegetation.
Date: May 26, 2006
Creator: Johnson, B J; Moore, K A; Lehmann, C; Bohlen, C & Brown, T A
Partner: UNT Libraries Government Documents Department

Mapping Alteration Caused by Hydrocarbon Microseepages in Patrick Draw area Southwest Wyoming Using Image Spectroscopy and Hyperspectral Remote Sensing

Description: Detection of underlying reservoir accumulations using remote sensing techniques had its inception with the identification of macroseeps. However, today we find ourselves relying on the detection of more subtle characteristics associated with petroleum reservoirs, such as microseeps. Microseepages are the result of vertical movement of light hydrocarbons from the reservoir to the surface through networks of fractures, faults, and bedding planes that provide permeable routes within the overlying rock. Microseepages express themselves at the surface in an array of alterations and anomalies, such as chemical or mineralogical changes in overlying soils and sediments. Using NASA's Hyperion hyperspectral imaging sensors, this project has developed spectral and geochemical ground truthing techniques to identify and map alterations caused by hydrocarbon microseepages and to determine their relationships to the underlying geology in the Patrick Draw area of Southwest Wyoming. Training the classification of satellite imagery with spectral inputs of samples collected over previously defined areas of hydrocarbon microseepage resulted in the successful identification of an anomalous zone. Geochemical characteristics of samples that defined this anomalous zone were then compared to the remaining non-anomalous samples using XRD, ICP, spectroscopy and carbon isotope techniques.
Date: June 21, 2008
Creator: Khan, Shuhab D.
Partner: UNT Libraries Government Documents Department

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?

Description: Cold bubbling springs in the Separation Creek area, the locus of current uplift at South Sister volcano show strong mantle signatures in helium and carbon isotopes and CO{sub 2}/{sup 3}He. This suggests the presence of fresh basaltic magma in the volcanic plumbing system. Currently there is no evidence to link this system directly to the uplift, which started in 1998. To the contrary, all geochemical evidence suggests that there is a long-lived geothermal system in the Separation Creek area, which has not significantly changed since the early 1990s. There was no archived helium and carbon data, so a definite conclusion regarding the strong mantle signature observed in these tracers cannot yet be drawn. There is a distinct discrepancy between the yearly magma supply required to explain the current uplift (0.006 km{sup 3}/yr) and that required to explain the discharge of CO{sub 2} from the system (0.0005 km{sup 3}/yr). This discrepancy may imply that the chemical signal associated with the increase in magma supply has not reached the surface yet. With respect to this the small changes observed at upper Mesa Creek require further attention, due to the recent volcanic vent in that area it may be the location were the chemical signal related to the uplift can most quickly reach the surface. Occurrence of such strong mantle signals in cold/diffuse geothermal systems suggests that these systems should not be ignored during volcano monitoring or geothermal evaluation studies. Although the surface-expression of these springs in terms of heat is minimal, the chemistry carries important information concerning the size and nature of the underlying high-temperature system and any changes taking place in it.
Date: April 30, 2002
Creator: van Soest, M.C.; Kennedy, B.M.; Evans, W.C. & Mariner, R.H.
Partner: UNT Libraries Government Documents Department

Transformation rates and fate of dissolved, colloidal and particulate forms of organic carbon in ocean margins. Final report, May 1, 1992--April 3, 1995

Description: The goal of this proposal was to develop new sampling and analytical techniques which could be used to understand the transformation rates and mechanisms of exchange between dissolved, colloidal, small particle and large particle size classes of organic carbon in ocean margins. To meet this goal, the authors focused on the development of cross-flow filtration (CFF) for the isolation of colloidal material from the dissolved phase in seawater. In addition, they tested and optimized high sensitivity techniques for the measurement of thorium isotopes using thermal ionization mass spectrometry (TIMS) and carbon isotopes using accelerator mass spectrometry (AMS) and stable C mass spectrometric techniques. In this final report, they highlight some of these new sampling and analytical developments as well as preliminary results from the first DOE cruise this past April. The report is broken down into 4 sections, namely (1) colloidal sampling strategies, (2) TIMS analytical developments, (3) carbon isotopic measurements and (4) results from the R/V Columbus Iselin cruise. For more detailed discussion of the findings, they have included as an appendix to this final report manuscripts which have been published or will be submitted during this funding cycle.
Date: November 1, 1998
Creator: Buesseler, K.O.; Moran, S.B.; Bauer, J.E. & Druffel, E.R.M.
Partner: UNT Libraries Government Documents Department

Dialogs by Jerry Szymanski regarding the Yucca Mountain controversy from December, 1990 to March, 1991: Volume 3. Special report number 9, Contract number 92/94.0004

Description: This report is a critical review of a US Geological Survey (USGS) paper regarding the origin of the Yucca Mountain calcite-opaline silica deposits. The report is in the form of a letter to the original authors in the USGS detailing the criticism regarding the origin of calcitic veins in the Yucca Mountain region. The USGS paper contributed most of these calcrete deposits to meteoric dissolution and precipitation mechanisms while the author presents his case for hydrothermal and magmatic origins. The paper presents strong isotopic characterization of these deposits to demonstrate a volcanic influence or source of this mineralization. Strontium, uranium, and carbon isotopes are graphed and compared from the numerous geologic and ground water samples available.
Date: July 1, 1993
Partner: UNT Libraries Government Documents Department


Description: Private- and public-sector stakeholders formed the new ''Trenton-Black River Appalachian Basin Exploration Consortium'' and began a two-year research effort that will lead to a play book for Trenton-Black River exploration throughout the Appalachian basin. The final membership of the Consortium includes 17 gas exploration companies and 6 research team members, including the state geological surveys in Kentucky, Ohio, Pennsylvania and West Virginia, the New York State Museum Institute and West Virginia University. Seven integrated research tasks are being conducted by basin-wide research teams organized from this large pool of experienced professionals. More than 3400 miles of Appalachian basin digital seismic data have been quality checked. In addition, inquiries have been made regarding the availability of additional seismic data from government and industry partners in the consortium. Interpretations of the seismic data have begun. Error checking is being performed by mapping the time to various prominent reflecting horizons, and analyzing for any anomalies. A regional geological velocity model is being created to make time-to-depth conversions. Members of the stratigraphy task team compiled a generalized, basin-wide correlation chart, began the process of scanning geophysical logs and laid out lines for 16 regional cross sections. Two preliminary cross sections were constructed, a database of all available Trenton-Black River cores was created, and a basin-wide map showing these core locations was produced. Two cores were examined, described and photographed in detail, and were correlated to the network of geophysical logs. Members of the petrology team began the process of determining the original distribution of porous and permeable facies within a sequence stratigraphic framework. A detailed sedimentologic and petrographic study of the Union Furnace road cut in central Pennsylvania was completed. This effort will facilitate the calibration of subsurface core and log data. A core-sampling plan was developed cooperatively with members of the isotope geochemistry ...
Date: April 1, 2004
Creator: Patchen, Douglas G.; Drahovzal, James; Wickstrom, Larry; Smith, Taury; Laughery, Chris & Avary, Katharine Lee
Partner: UNT Libraries Government Documents Department

Leakage and Seepage in the Near-Surface Environment: An Integrated Approach to Monitoring and Detection

Description: Monitoring and detection of leakage and seepage of carbon dioxide (CO{sub 2}) in the near-surface environment is needed to ensure the safety and effectiveness of geologic carbon sequestration. Large leakage fluxes, e.g., through leaking wells, will be easier to detect and monitor than slow and diffuse leakage and seepage. The challenge of detecting slow leakage and seepage is discerning a leakage or seepage signal from within the natural background variations in CO{sub 2} concentration and flux that are controlled by a variety of coupled processes in soil. Although there are no direct examples of leaking geologic carbon sequestration sites on which to base a proposed verification approach, we have been guided by our prior simulation studies of CO{sub 2} leakage and seepage, which showed that large CO{sub 2} concentrations can develop in the shallow subsurface even for relatively small CO{sub 2} leakage fluxes. A variety of monitoring technologies exists for measuring CO{sub 2} concentration and flux, but there is a gap between instrument performance and the detection of a leakage or seepage signal from within large natural background variability. We propose an integrated approach to monitoring and verification. The first part of our proposed approach is to characterize and understand the natural ecosystem before CO{sub 2} injection occurs so that future anomalies can be recognized. Measurements of natural CO{sub 2} fluxes using accumulation chamber (AC) and eddy correlation (EC) approaches, soil CO{sub 2} concentration profiles with depth, and carbon isotope compositions of CO{sub 2} are needed to characterize the natural state of the system prior to CO{sub 2} injection. From this information, modeling needs to be carried out to enhance understanding of carbon sources and sinks so that anomalies can be recognized and subject to closer scrutiny as potential leakage or seepage signals. Long-term monitoring using AC, EC, and soil-gas ...
Date: December 18, 2003
Creator: Oldenburg, Curtis M. & Lewicki, Jennifer L.
Partner: UNT Libraries Government Documents Department

Heterogeneous Shallow-Shelf Carbonate Buildups in the Paradox Basin, Utah and Colorado: Targets for Increased Oil Production and Reserves Using Horizontal Drilling Techniques

Description: The Paradox Basin of Utah, Colorado, Arizona, and New Mexico contains nearly 100 small oil fields producing from carbonate buildups within the Pennsylvanian (Desmoinesian) Paradox Formation. These fields typically have one to 10 wells with primary production ranging from 700,000 to 2,000,000 barrels (111,300-318,000 m{sup 3}) of oil per field and a 15 to 20 percent recovery rate. At least 200 million barrels (31.8 million m{sup 3}) of oil will not be recovered from these small fields because of inefficient recovery practices and undrained heterogeneous reservoirs. Several fields in southeastern Utah and southwestern Colorado are being evaluated as candidates for horizontal drilling and enhanced oil recovery from existing vertical wells based upon geological characterization and reservoir modeling case studies. Geological characterization on a local scale is focused on reservoir heterogeneity, quality, and lateral continuity, as well as possible reservoir compartmentalization, within these fields. This study utilizes representative cores, geophysical logs, and thin sections to characterize and grade each field's potential for drilling horizontal laterals from existing development wells. The results of these studies can be applied to similar fields elsewhere in the Paradox Basin and the Rocky Mountain region, the Michigan and Illinois Basins, and the Midcontinent region. This report covers research activities for the first half of the fourth project year (April 6 through October 5, 2003). The work included (1) analysis of well-test data and oil production from Cherokee and Bug fields, San Juan County, Utah, and (2) diagenetic evaluation of stable isotopes from the upper Ismay and lower Desert Creek zones of the Paradox Formation in the Blanding sub-basin, Utah. Production ''sweet spots'' and potential horizontal drilling candidates were identified for Cherokee and Bug fields. In Cherokee field, the most productive wells are located in the thickest part of the mound facies of the upper Ismay zone, ...
Date: October 5, 2003
Creator: Chidsey, Thomas C.; McClure, Kevin & Morgan, Craig D.
Partner: UNT Libraries Government Documents Department

GAMA-LLNL Alpine Basin Special Study: Scope of Work

Description: For this task LLNL will examine the vulnerability of drinking water supplies in foothills and higher elevation areas to climate change impacts on recharge. Recharge locations and vulnerability will be determined through examination of groundwater ages and noble gas recharge temperatures in high elevation basins. LLNL will determine whether short residence times are common in one or more subalpine basin. LLNL will measure groundwater ages, recharge temperatures, hydrogen and oxygen isotopes, major anions and carbon isotope compositions on up to 60 samples from monitoring wells and production wells in these basins. In addition, a small number of carbon isotope analyses will be performed on surface water samples. The deliverable for this task will be a technical report that provides the measured data and an interpretation of the data from one or more subalpine basins. Data interpretation will: (1) Consider climate change impacts to recharge and its impact on water quality; (2) Determine primary recharge locations and their vulnerability to climate change; and (3) Delineate the most vulnerable areas and describe the likely impacts to recharge.
Date: December 12, 2011
Creator: Singleton, M J; Visser, A; Esser, B K & Moran, J E
Partner: UNT Libraries Government Documents Department

Effect of thermal decarbonation on the stable isotope composition of carbonates

Description: The unusual texture and stable isotope variability of carbonates in AH84001 have been used as evidence for early life on Mars (Romanek et al., 1994; McKay et al., 1996). Oxygen and carbon isotope variability is most commonly attributed to low-temperature processes, including Rayleigh-like fractionation associated with biological activity. Another possible explanation for the isotopic variability in meteoritic samples is thermal decarbonation. In this report, different carbonates were heated in a He-stream until decomposition temperatures were reached. The oxygen and carbon isotope ratios ({delta}{sup 18}O and {delta}{sup 13}C values) of the resulting gas were measured on a continuous flow isotope ratio mass spectrometer. The aim of this work is to evaluate the possibility that large isotopic variations can be generated on a small scale abiogenically, by the process of thermal decarbonation. Oxygen isotope fractionations of >4{per_thousand} have been measured during decarbonation of calcite at high temperatures (McCrea, 1950), and in excess of 6{per_thousand} for dolomite decarbonated between 500 and 600 C (Sharma and Clayton, 1965). Isotopic fractionations of this magnitude, coupled with Rayleigh-like distillation behavior could result in very large isotopic variations on a small scale. To test the idea, calcite, dolomite and siderite were heated in a quartz tube in a He-stream in excess of 1 atmosphere. Simultaneous determinations of {delta}{sup 13}C and {Delta}{sup 18}O values were obtained on 250 {micro}l aliquots of the CO{sub 2}-bearing He gas using an automated 6-way switching valve system (Finnigan MAT GasBench II) and a Finnigan MAT Delta Plus mass spectrometer. It was found that decarbonation of calcite in a He atmosphere begins at 720 C, but the rate significantly increases at temperatures of 820 C. After an initial light {delta}{sup 18}O value of -14.1{per_thousand} at 720 C associated with very early decarbonation, {delta}{sup 18}0 values increase to a constant -11.8{per_thousand}, close to the ...
Date: January 1, 2001
Creator: Durakiewicz, T. (Tomasz); Sharp, Z. D. (Zachary D.) & Papike, J. J. (James Joseph),
Partner: UNT Libraries Government Documents Department