Astronomical signatures in Late Devonian black shales of the Rhenish Massif.

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The Late Devonian (380 – 359 million years ago (Ma)) was a time of dynamic climate change, episodic ocean anoxia, biodiversity loss and innovation. The entanglement of these developments is best illustrated by the Late Devonian mass extinction event at the Frasnian–Famennian boundary (374 Ma). Yet, the entire Late Devonian represents a complete reorganization of marine ecosystems, in a series of extinction events associated with ocean anoxia (e.g. Kellwasser, Annulata, Dasberg and Hangenberg crises). In the Rhenish Massif, the sedimentologic expression of this series of extinctions has been studied since almost 200 years (von Dechen, 1823), which makes the Rhenish Massif extremely well-documented in terms of lithostratigraphy, microfacies, biostratigraphy and faunal assemblages. The next important step is understanding the cyclicity of Devonian sedimentary sequences in the Rhenish Massif, first to refine the geological time scale and second to provide paleoclimate insights for this high-CO2 world. With this proposal, I am requesting the means to construct accurate and consistent astrochronologies for three Late Devonian time slices at three different field sites: The Kellwasser events at the Winsenberg roadcut near Diemelsee-Adorf; the Annulata and Dasberg crises at the Effenberg Quarry; and the Hangenberg crisis at the Borkewehr section. The research team will seek to combine cyclostratigraphic age-depth models with well-established biostratigraphies to provide global correlations towards other Late Devonian reference sections. This approach could yield valuable new constraints for the geologic time scale. However, the main objective of this proposal resides with the fact that accurate astrochronologies constitute a prerequisite to quantify rates and durations of Late Devonian climate and carbon-cycle processes. For example, the development of ocean anoxic conditions. This proposal provides a unique opportunity to evaluate the role of astronomical Milankovitch forcing in prompting and pacing Late Devonian carbon cycle perturbations and extinction pulses.