CYCLOSTRATIGRAPHY AND ASTROCHRONOLOGY OF THE LATE DEVONIAN KELLWASSER CRISIS, NORTHERN APPALACHIAN BASIN, USA

The Late Devonian marine mass extinctions occurred in a succession of pulses within a narrow stratigraphic interval known as the Kellwasser Crisis. An expanded 32 m thick cyclic marine sedimentary section at Walnut Creek, Chautauqua County, New York, USA permits investigation of the Kellwasser Crisis interval at an unprecedented high resolution. Magnetic susceptibility measurements reveal that the Walnut Creek sediments have Milankovitch-like stratigraphic patterns. Astrochronology developed from tuning to interpreted obliquity cycles indicates a 900 k.y. duration for the Kellwasser Crisis. Spectral analysis reveals that sedimentary cycles are characterized by strong precession-eccentricity forcing over the lower 600 k.y; this rapidly shifts to dominant obliquity forcing in the final 300 k.y. leading up to the Frasnian-Fammenian boundary. This shift may herald rapid growth of a high-latitude ice sheet during the latter part of the Kellwasser Crisis, supporting hypotheses for glaciation at the end of the Frasnian age. Finally, the Walnut Creek astrochronology contributes to a significant reduction of uncertainty in the Devonian time scale.