ORBITAL CYCLOSTRATIGRAPHY WITHIN THE LATE DEVONIAN KELLWASSER CRISIS INDICATED BY MAGNETIC SUSCEPTIBILITY IN WESTERN NEW YORK STATE – PRELIMINARY RESULTS

The Kellwasser Crisis occurred between 371.85 and 372.55 Ma, during the latest Frasnian, culminating in the Franian-Famennian boundary. In the northern Appalachian Basin of western New York the strata of this interval are dominated by gray shales that contain interbedded black shales, thin carbonate beds, and baritic or calcareous concretionary horizons, as well as several tephera horizons. The Pipe Creek Shale is correlative to the Lower Kellwasser Bed; the Pt. Gratiot Bed, 0.78 m below the base of the Dunkirk Formation, is correlative to the Upper Kellwasser Bed.

The Kellwasser Interval strata, continuously exposed along Walnut Creek in Chautauqua County, NY, were sampled at 5cm increments from below the Pipe Creek Shale in the Angola Formation through the Hanover Formation, and into the lower Dunkirk Formation, a total of 32 m, and analyzed for bulk magnetic susceptibility. The large quantity of sample points allowed for a high-resolution representation of the cyclic nature of the strata deposited during the Kellwasser Crisis. Five periods of cyclicity were detected through spectral analysis. Eight cycles are consistent with a 100,000 year orbital eccentricity, 21 cycles correlate with the obliquity cycle, and 40 cycles correlate with the precession cycle based on 800,000 years for the interval. Eight tephra horizons below the Pipe Creek Shale and in the Hanover Shale above and below the Pt. Gratiot Bed are expected to further constrain the geochronometrc interval of the cycles.