On the Isotopic Analyses of Oxygen and Carbon of Marine Biogenic Carbonates such as Corals and Pelecypods

Abstract

Corals and pelecypods of Recent to Pleistocene age were analyzed for their isotopic ratio of oxygen and carbon by means of McCrea's technique. The precision and reproducibility of the isotopic analysis were found to be±0.08‰ forδ¹⁸ O and±0.15permil; forδ13C based on the analyses of NBS-20limestone over a period of six months. The effect on the isotopic ratio of roasting presentday and fossil carbonates in purified helium was also examined. In order to calibrate our standards against PDB scale, three different standards, of which the isotopic ratios have been corrected against the scale, were analyzed to gether with our standards. The results were, however, not consistent with each other and further study will be carried out to settle the problem. It was shown that the diagenetic alteration of aragonite skelton of Pleistocene coralsresulted in the depletion of13C in parallel with calcitization and dissolution of uranium.