TESTING LIQUID DECARBONATION TEMPERATURE AND TIME FOR δ13CORG ANALYSES IN SEDIMENTARY SECTIONS
Liquid decarbonation for organic carbon isotope analysis involves a timed soak of a powdered sample in acid followed by a series of rinses, but is not standardized from lab to lab. We hypothesize that differences in the temperature and length of decarbonation may leave carbonate phases in δ13Corg analyses, as different carbonate minerals are more or less recalcitrant during acid digestion (e.g., calcite, dolomite, siderite). Complete removal of carbonate is critical to δ13Corg analyses because δ13Ccarb has a heavy isotopic signature and leads to a more positive δ13Corg value if unintentionally left in the sample. Here, we test different decarbonation temperatures (20,70, and 80ºC) and lengths of time (10, 60, 120, 240, and 480 minutes) for several geologic samples, some of which contain dolomite. Our preliminary results indicate samples containing dolomite heated at higher temperatures exhibit a lighter δ13Corg isotopic value, suggesting more complete removal of carbonate occurs at higher temperatures. We will report these analyses and discuss the problems associated with this method, including possible solubilization of organic carbon.