Paper No. 142-7
Presentation Time: 9:55 AM
MILLENNIAL-SCALE CYCLES IN THE UPPER DEVONIAN SHALES OF THE HANOVER FORMATION, JAVA GROUP, APPALACHIAN BASIN, WESTERN NEW YORK
Interbedded black to light gray shales of the Java Group in western New York State represent pro-deltaic deep shelf to basin deposits on the eastern margin of the Appalachian Basin in the high Frasnian of the Upper Devonian. 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 represent 800,000 years, where the eccentricity, obliquity, and precession oscillations are visible as packages and decimeter to meter thick couplets of black and light gray shales.
The 2.5 m thick interval of lower Hanover Formation from the West Valley NX-1 core (API# 31-009-06740-00-00; 880.2’ to 884.5’) represents 40,635 years in our calculations. The core was sampled continuously at 1 cm intervals for MS. The data were analyzed using a Fourier-Transform analysis which yielded three strong cycles: 16-21 ky, 10-16 ky, and 2.1-2.5 ky in duration. The 10-21 ky cycles fall within the range of the precession oscillation for the Upper Devonian. The 2.1-2.5 ky cycle is consistent with the Hallstatt astronomical oscillation that is modulated by the Jovian planets and has been recognized in Devonian to Holocene strata. This cycle is visible in outcrop and the core as 4 to 10 cm thick dark and light gray shale couplets.