ROCK MAGNETIC CYCLOSTRATIGRAPHY OF THE MISSISSIPPIAN MAUCH CHUNK FORMATION, POTTSVILLE, PENNSYLVANIA (Invited Presentation)

A rock magnetic cyclostratigraphy study of the Pottsville, PA outcrop of the Mississippian Mauch Chunk Formation was conducted using magnetic susceptibility (MS) measured by both an SM-20 portable susceptibility meter in the field and on samples measured in the laboratory using a KLY-3s Kappabridge susceptibility meter. The objective was to determine if the fluvial, 330 Ma sedimentary rocks could record astronomically-forced global climate cycles. A detailed magnetostratigraphic study of this outcrop (DiVenere and Opdyke, 1991) revealed a 100 m thick normal polarity event that Opdyke et al. (2014) indicate to be ~1000 kyr in duration based on a regional correlation in northeastern North America of magnetozones and biostratigraphy, providing a chronostratigraphic framework for the cyclostratigraphy. Unoriented samples for laboratory analysis and three measurements of in situ magnetic susceptibility were collected every 0.5 m from 68 m of section. The portable susceptibility meter time series shows hierarchical cycles that did not obviously correlate with the red shales and sandstone beds throughout the section. Multi-taper method (MTM) spectral analysis and robust red noise modeling showed significant spectral peaks with stratigraphic thickness wavelengths of 8 and 6 m, 1.9 m, and 1.0 m. These peaks were also observed in the laboratory measured susceptibilities; however, they did not rise above the 95% confidence level of the robust red noise. If the 6 m peak is assigned to the 95 kyr short eccentricity cycle, the 8 m peak is ~125 kyr short eccentricity, the 1.9 m peak is 30 kyr obliquity, and the 1.0 m peak is 16.5 kyr precession, consistent with predictions for obliquity and precession at 330 Ma (Waltham, 2015). These fluvial sedimentary rocks appear to record Milankovitch cycles by variations in the concentration of magnetic minerals, possibly reflecting changes in stream discharge.