Short Local Expression, Long Global Crisis: Astronomical Constraints on Devonian Kellwasser Event Durations from Walnut Creek (New York State, USA)

The Frasnian-Famennian Kellwasser Crisis (~372 Ma) is one of the most severe marine biocrises of the Phanerozoic Eon. The ecological impact of the Kellwasser Crisis was global in nature and sedimentary sections that record the Kellwasser Crisis commonly contain two organic-rich layers, the Lower Kellwasser (LKW) and Upper Kellwasser (UKW) horizons. This canonical two-step pattern, however, is far from globally uniform and differences in thickness, completeness and lithology are pronounced among depositional settings. Cyclostratigraphic analyses converge in total crisis duration estimates, while high resolution studies reveal substantial differences in the duration and internal structure of the LKW and UKW depending on depositional environment. These differences challenge the assumption that the Kellwasser horizons are isochronous at fine timescales and highlight the need for high-resolution analyses across multiple depositional environments.

To address these uncertainties, we present a cyclostratigraphic and paleoclimatic analysis of a combined sediment core and hand sample dataset of the siliciclastic Walnut Creek section (western New York State, USA). Walnut Creek exhibits a pronounced meter-scale rhythmicity between thicker grey shales and thinner black shale beds that is suggestive of astronomical forcing.

Cyclostratigraphic reconstruction based on XRF analysis indicates a total crisis duration of ~880 kyr, which is consistent with independent estimates from other localities. However, reconstructed durations of ~25 kyr for the LKW and ~8 kyr for the UKW are notably shorter than observed elsewhere. Throughout the crisis interval, black shale deposition in the Appalachian Basin is indicated to be driven by top-down eutrophication linked to precession-paced variations in monsoon strength. The new geochemical and cyclostratigraphic evidence from Walnut Creek demonstrates that the onset of organic-rich LKW and UKW deposition was likely isochronous in the Appalachian Basin and the deeper Rheic Ocean margin, and that astronomical forcing controlled the pacing of the crisis. Notably, the thick organic-rich crisis beds commonly found in deposits from the Rheic Ocean correspond to several, respectively shorter, precession-paced black shale beds at Walnut Creek.

From these findings we identify three first-order factors that locally determine whether LKW and UKW organic-rich horizons formed, how thick they would become, and how long they persisted: (1) the capacity of the hinterland to generate nutrient-rich soils; (2) the sensitivity of the depositional environment to precessional forcing; and (3) the dissipation timescales of oxygen-depleted water masses. Together, these factors explain the global spatial heterogeneity of the geologic expression of the Kellwasser Crisis.