The carbonate skeleton of recent and fossil Coleoidea: Biological, physical or diagenetic control?

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This project focuses on the structure and function of internal carbonate skeletons of recent and fossil Coleoidea (Sepia, belemnites) and their geochemical signals. It aims at understanding to which extent the geochemical composition of these skeletons, widely used by stratigraphers, geochemists and palaeoclimatologists is controlled by palaeobiological (1), physical (2) and/or diagenetic factors (3). We thereby clearly cover the interface of biology, autecology and diagenesis. 1. Cuttlebones of recent Sepia spp. suggest significantly different growth rates for tropical and high latitudinal taxa, a factor that may apply for belemnites as well. Different morphological groups of belemnites may have had a different ontogeny, occupying different habitats. This should be mirrored in the geochemical signals reflecting the composition of the ocean water. 2. Temperature and salinity seem to be the main physical factors controlling the composition of the belemnite guards. We want to clearly differentiate between both factors by using a geochemical multi proxy approach (δ18O, δ13C, Mg/Ca). 3. Potential diagenetic overprint, crucial for the interpretation of the signals, will be tested. By applying various techniques (SEM, cathodoluminiscence analyses, EBSD, microprobe, elemental analyses) to thin sections of various morphotypes, differential degrees of diagenetic alteration should be defined.