Combined high-precision Δ48 and Δ47 analysis of carbonates

High-precision analysis of the excess abundance (relative to the stochastic distribution) of mass 48 isotopologues in CO2 evolved from acid digestion of carbonates (Delta(48)) has not been possible until recently due to the relatively low natural abundance of O-18. Here we show that the 253 Plus (TM) gas source mass spectrometer equipped with Faraday cups and 10(13) Omega resistors can perform combined Delta(47 )and Delta(48) analyses on carbonates with external reproducibilities (1SD) of 0.010 parts per thousand and 0.030 parts per thousand, respective. similar to 10 mg aliquots of five carbonate reference materials (ETH 1, ETH 2, ETH 3, ETH 4, and Carrara) are digested with phosphoric acid at 90 degrees C using a common acid bath. The evolved CO2 is purified using an automated gas preparation system (including cryotraps and a GC) and analyzed for its Delta(47) and Delta(48) compositions using the dual inlet system of a 253 Plus (TM) gas source mass spectrometer. Raw Delta(47) and Delta(48) values are finally normalized to the Carbon Dioxide Equilibrium Scale (CDES). In Delta(47), (CDES 90 degrees C )vs. Delta(48), CDES 90 degrees C space, calcite reference materials Carrara, ETH 3 and ETH 4 agree with the equilibrium curve for calcite after adding semi-empirically determined 90 degrees C acid fractionation factors of 0.196 parts per thousand (for Delta(47)) and 0.136 parts per thousand (for Delta(48)) to theoretica Delta(63) and Delta(64 )data. Agreement between measured and theoretically expected Delta(48), CDES 90-c highlights the accuracy of our high-precision clumped isotope analytical setup. Combined analysis of the abundances of mass 47 and mass 48 isotopologues in CO(2 )evolved from acid digestion of natural carbonates has excellent potential for the determination of accurate and highly precise paleotemperatures as well as for the identification of rate-limiting kinetic processes involved in biomineralization. A formation temperature of 15( +/- 2) degrees C is obtained on the 95 % confidence level for the Upper Cretaceous chalk sample ETH 3.