Milankovitch Forcing and the Timing and Pacing of Devonian Anoxic Events

The Devonian represents a warmer-than-present period in Earth’s history (419 – 359 million years ago), characterized by a series of pulsed, globally expressed perturbations – anoxic events associated with elevated extinction rates, climate changes, disruption of biogeochemical cycles, sea-level fluctuations, and deposition of organic-rich strata. Despite decades of research, no consensus has emerged on their causal mechanisms. In recent years, mounting evidence has suggested that astronomical forcing may be linked to their rhythmic recurrence, raising the possibility that Milankovitch cycles structured the timing and pacing of Devonian anoxic events. This thesis integrates cyclostratigraphy and geochemistry within a broader stratigraphic framework, applying a multi-proxy approach to three records from two basins to evaluate how astronomical forcing shaped Devonian environmental variability across more than 30 million years. Floating astrochronologies constrain the durations of the global Daleje, Choteč, Kačák, pumilio, and Rhinestreet events, the Kellwasser Crisis as well as the regional Fir Tree, Hubbard Quarry, and Lodi events. Their temporal positions relative to orbital extrema reveal distinct patterns, indicating that astronomical forcing exerted a major influence on both their timing and pacing. Long-period, multi-million-year astronomical modulation cycles provided the background state that governed when environmental perturbations were likely to occur, while canonical Milankovitch forcing controlled short-period pacing and may have acted as immediate triggers. Two conceptual models emerge: an Upper-Threshold Model, in which events occur during maxima in long-term modulation cycles and reflect periods characterized by strong climatic alternation, and a Lower-Threshold Model, in which events arise during modulation minima, reflecting comparatively muted climatic variability and enhanced stagnation. Together, these models explain contrasting event expressions across basins, the diachroneity of anoxia, and the selective recurrence of global events versus regional perturbations without requiring assumptions about specific Earth-system boundary conditions. The framework developed here provides a benchmark for interpreting astronomically paced environmental change throughout the Phanerozoic and highlights the central role of astronomical forcing in shaping global anoxic events.