Project Details
Projekt
Chemical and mineralogical changes of calcareous shell material during fossilisation processes – an experimental approach
Subject Area
Palaeontology
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 348043586
Bivalve shells are incrementally growing hard tissues that record biological and environmental information of aquatic settings in precise chronological order over timespans of years to centuries. In contrast, eggshells are fast mineralising (hours to days) hard tissues from amniotes recording information on diet, body temperature, and climate in terrestrial settings. We plan to investigate the post-mortem alteration of these biomineralised carbonate shell materials and the stability of recorded mineralogical, chemical and microtextural proxy information by in-vitro diagenesis experiments. Understanding the diagenetic alteration of bivalve shells and eggshells is paramount for reliable palaeoclimatic and palaeoenvironmental reconstructions from fossils. A critical factor of shell preservation and diagenesis are dissolution and reprecipitation processes of the calcareous shell material, leading to the formation of neomorphic CaCO3 minerals or domains within existing biomineral units, which changes the chemical and isotopic composition of the shell as well as the shell microstructure. Only a limited number of experimental studies, mostly heating at high temperatures under dry conditions or hydrothermal alteration, systematically investigated chemical and mineralogical alteration of bivalve shells but none of eggshells. Low-temperature (≤90 °C) experiments at typical near-surface burial and fluid conditions, however, are lacking. In the proposed study, we will perform controlled in-vitro alteration experiments of bivalve shell and eggshell material in different isotopically labelled aqueous solutions (freshwater and seawater), mimicking the composition of typical diagenetic fluids, to assess the resistance of key environmental, climatic and dietary proxies against diagenetic processes. Mineralogical, chemical, and microstructural changes of the calcareous hard parts as well as the intra-crystalline protein phase will be investigated along hard part alteration gradients in-situ and ex-situ using a combination of bulk and spatially highly resolved in-situ analytical techniques. The study material will be chemically and structurally characterised before and after the in-vitro low-temperature alteration to identify diagenetic features, which will then be compared to fossil bivalve and eggshell samples. The overarching goal is to gain a better mechanistic understanding of shell fossilisation processes in low temperature settings and the preservation potential of chemical, isotopic and microtextural proxies, both in the biomineral and the organic phase of these calcareous hard tissues.
DFG Programme
Research Units
Subproject of
FOR 2685:
The Limits of the Fossil Record: Analytical and Experimental Approaches to Fossilization
Co-Investigator
Dr. Eric Otto Walliser
