tailieunhanh - 13C–18O bonds in carbonate minerals: A new kind of paleothermometer

The abundance of the doubly substituted CO2 isotopologue, 13C18O16O, in CO2 produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of 13C–18O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 C by the function: D47 = Æ 106 Æ T 2 , where D47 is the enrichment, in per mil, of 13C18O16O in CO2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO2 isotopologues, and T is the. | Available online at Geochimica ELSEVIER Geochimica et Cosmochimica Acta 70 2006 1439-1456 locate gca 13C-18O bonds in carbonate minerals A new kind of paleothermometer Prosenjit Ghosh a Jess Adkins a Hagit Affek a Brian Balta a Weifu Guo a Edwin A. Schauble b Dan Schrag c John M. Eiler a a Division of Geological and Planetary Sciences California Institute of Technology Pasadena CA 91125 USA b Department of Earth and Space Sciences University of California Los Angeles Los Angeles CA 90095 USA c Department of Earth and Planetary Sciences Harvard University Cambridge MA 02138-2902 USA Received 2 August 2005 accepted in revised form 10 November 2005 Abstract The abundance of the doubly substituted CO2 isotopologue 13C18O16O in CO2 produced by phosphoric acid digestion of synthetic inorganic calcite and natural biogenic aragonite is proportional to the concentration of 13C-18O bonds in reactant carbonate and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50 C by the function D47 106 T 2 where D47 is the enrichment in per mil of 13C18O16O in CO2 relative to the amount expected for a stochastic random distribution of isotopes among all CO2 isotopologues and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry where the temperature-dependent property of interest is the state of ordering of 13C and 18O in the carbonate lattice . bound together vs. separated into different CO32- units and not the bulk b18O or b13C values. Current analytical methods limit precision of this thermometer to ca. 2 C 1r. A key feature of this thermometer is that it is thermodynamically based like the traditional carbonate-water paleothermometer and so is suitable for interpolation and even modest extrapolation yet is rigorously independent of the b18O of water and b13C of DIC from which carbonate .