Cyclostratigraphy in deep time: lessons from Devonian strata in the Rhenish Massif

Over the past decades, cyclostratigraphy has been used to refine the Cenozoic timescale, and evidence for astronomical forcing of major climatic events has been identified in numerous records. Progress also has been made in the Mesozoic, although the absence of astronomical solutions complicates this effort. The next frontier for cyclostratigraphy is the Paleozoic. This talk will outline some of the challenges of cyclostratigraphy in deep time, using examples from the Late Devonian of the German Rhenish Massif. The Late Devonian saw repeated occurrences of widespread anoxia, some of which were associated with mass extinctions. The recurrent nature of these anoxic events suggests that astronomical forcing could have played a role in their initiation. Investigating this hypothesis requires an integrated stratigraphic approach. The cyclic deep-marine successions of the Rhenish Massif have been studied for over a century. This research history has culminated in many well-described outcrops with detailed litho-, bio-, and chemostratigraphy, ideal for cyclostratigraphy. Analysis of three sections that record the Kellwasser, Annulata, Dasberg, and Hangenberg biotic crises supports the hypothesis that these events were at least partially controlled by astronomical forcing. Furthermore, we show that cyclostratigraphy can be used to refine the Devonian timescale – if a consensus based on astrochronologies from various sites can be reached. With more and more cyclostratigraphic works being published, an astrochronological framework for the Late Devonian is starting to emerge, and the Rhenish Massif will be a key region to further develop this framework in the coming years.