No vital effect on δ 18O and δ 13C values of fossil brachiopod shells, Middle Devonian of China

Abstract

Biogenic fractionation (vital effect) of carbon and oxygen isotopes during metabolism is ubiquitous among marine organisms. Whether there is vital effect on the isotopic compositions of fossil brachiopods represents one of the most controversial issues in the carbonate stable isotope geochemistry. Furthermore, the problem involves not only the feasibility of the utilization of fossil brachiopod shells as analysis samples for obtaining the original carbon and oxygen isotopic compositions of carbonates, but also the credibility of the data and conclusions already achieved in the study field. With fossil brachiopods from Middle Devonian of China, this study investigates the vital effect by comparisons of δ 18O and δ 13C between the fossils of the same original living environment and the shell’s preservation at levels of species, genus, and family. No systematic differences of δ 18O and δ 13C between fossils were found, which led to the conclusion that no detectable vital effect occurred in the fossil brachiopod shells. The argument that the fossil brachiopod possibly has biogenic fractionation with the stable isotopes of carbon and oxygen resulted likely from studies of fossils that are different in the original living environment or the state of preservation.