Quantification of diagenetic overprint processes of fossil carbonate skeletons derived from geological laboratories and from hydrothermal alteration experiments

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Recrystallization of the original organism-specific microstructure of carbonate skeletons of fossil marine invertebrates is a clear indicator for diagenetic overprint. Microstructural data, which mirror recrystallization, are of great value for the assessment of geochemical proxies that are obtained from carbonate fossils for the reconstruction of environmental conditions. Quantitative data on microstructures and their changes can be measured by Electron-Backscatter-Diffraction (EBSD). EBSD allows submicrometer-resolution mapping of mineral phase and crystallo¬graphic orientation of grains, grain morphologies, grain boundary orientations, and internal mosaic structure of crystals. The method thus provides the necessary quantitative assessment of pristine and recrystallized microstructures. In the first funding period of CHARON the group of the proposer has laid foundations for the quantitative analysis of fossil microstructures. In this second funding period a twofold approach will be pursued: (1) analysis of fossils from geological laboratories: basins with a well-characterized diagenetic history, and (2) kinetic time-temperature series of laboratory-based hydrothermal alteration. We aim to obtain a quantitative correlation of the diagenetic geothermal heat flow of the selected well-studied basins with the mineralogical and geochemical composition and the micro/meso-structural state of the carbonate fossils. The selected natural laboratories cover regional temperature fields of 50°C, 100-120°C, 150-200°C, and up to 350 °C, respectively.