MODERN ELEMENTAL AND ISOTOPIC CHEMISTRY OF ECHINODERM SKELETAL CARBONATE

Fossil echinoderms have recently been suggested by Dickson to record oscillations in the oceanic Mg/Ca ratio through the Phanerozoic. Such a supposition, however, must be based on a firm understanding of the skeletal chemistry of modern echinoderms as well as the changes such material would undergo during diagenesis. While datasets have been generated to characterize the chemistry of modern echinoderm skeletal material (e.g. those of Clark and Wheeler, Vinogradov, Chave, Weber), the lack of paired stable isotope and elemental analyses on splits of identical material has hampered their application to diagenetic studies of fossil echinoderms. In this study we extend the utility of these literature datasets by reviewing and interpreting them within the context of new coupled elemental (Mg/Ca, Sr/Ca, Fe/Ca, Mn/Ca) and isotopic (δ¹³C, δ¹⁸O) data from the skeletal carbonate of modern crinoids.

Since echinoderm skeletal material has a high proportion of occluded organic matter (~50%), methods for cleaning echinoderm skeletal carbonate were also investigated. It was found that the chemistry of ossicles cleaned with NaOCl, H2O2, or enzymatic cleaner were identical to the control (no cleaning method applied) with the exception that in the case of the enzymatic cleaner δ¹³C was more positive by ~ 1‰.