PRECESSION AND SUB-PRECESSION CYCLES WITHIN THE HANOVER FORMATION, JAVA GROUP, UPPER DEVONIAN, WESTERN NEW YORK STATE

Along Walnut Creek, near the Village of Silver Creek, New York, the high Frasnian-lowest Famennian (Upper Devonian) Hanover Formation is predominantly composed of interbedded bioturbated light gray silty shales and dark gray organic-rich silty shales. These shales were deposited in a pro-deltaic deep shelf to basin setting on the eastern margin of the Appalachian Basin. Milankovitch-scale and sub-precession millennial-scale climatic cycles were detected by changes in bulk magnetic susceptibility (MS). The MS values were framed by the distinct biostratigraphically constrained and radiometrically dated Pipe Creek Formation, which is equivalent to the Lower Kellwasser interval, and the Pt. Gratiot Bed, which is equivalent to the Upper Kellwasser interval. The 30 m thick strata measured in outcrop represents 800,000 years where the eccentricity, obliquity, and precession oscillations are visible as packages in decimeter to meter thick couplets of dark and light gray shales.

A 4.87-meter thick interval of the middle Hanover Formation from the West Valley NX-1 core (API# 31-009-06740-00-00; 830’ to 846’) represents 92,516 years in our calculations. The core was sampled continuously at 1 cm intervals for MS. The data were analyzed using a Fourier-Transform analysis within time intervals of 82,516, 92,516, and 102,516 years where the 100 Ky short orbital eccentricity cycle was used as a geochronometer for astronomical calibration. Five strong cycles at 20, 10-11, 7, 3.2-3.3, and 2-2.05 Ky were detected. The 20 Ky cycle corresponds to the 16.9-20 Ky Devonian precession cycle. The 10-11 and 7 Ky cycles are thought to be combination tones of Milankovitch cycles, which were also observed from a different interval within the West Valley core in an earlier study. The 3.2-3.3 Ky peak could be the result of solar forcing related to the Hallstatt cycle which occurred at an interval of 2.5 Ky during the Devonian. The 2-2.05 Ky peak could be a periodic climate change at the millennial scale related to internal mechanisms such as ice sheet dynamics and ocean-atmosphere variations.