ASTRONOMICALLY FORCED CYCLICITY IN THE UPPER ORDOVICIAN UTICA SHALE, TACONIC FORELAND BASIN, MOHAWK VALLEY REGION, NY, USA

The Late Ordovician Utica Shale was deposited in a subsiding foreland basin associated with the Taconic orogeny. The purpose of this work is to determine whether astronomical forcing via Milankovitch cycles is recorded in the sedimentary geochemistry of cores 74NY10 and 75NY2 from the Mohawk Valley region, NY.

Recently published high precision dates of Utica K-bentonites, together with the expected 405 Kyr metronome and the 100 Kyr short eccentricity cycle, provide the opportunity to devise a high-resolution astrochronology useful for testing predicted frequencies of precession and obliquity cycles during the Ordovician and for better defining the age of the base of the Katian Stage as well as understanding environmental controls on Utica graptolite communities.

Following several recent studies, a PCA (Principal Component Analysis) will be conducted in MATLAB to extract the 3 principal components from over 30 analyzed elements. Interpolation to a uniform spacing and resampling will be conducted with Analyseries 2.0.4.2. Spectrum analysis will be done with the Multitaper Method (MTM) and Wavelet. Eccentricity and obliquity cycles will be extracted with Gaussian band-pass filters in Analyseries 2.0.4.2 and Taner band-pass filters in MATLAB. Signal envelopes of the filtered series will be computed using Hilbert transformation. MTM power spectral analysis will be used to determine the significance of the cycles’ peaks. Resampling and filtering the data may create artifacts. Consequently, we will conduct analyses in PAST 3.17 using the REDFIT method, which doesn’t require evenly spaced data and, therefore, does not require resampling. By comparing results from independent methods, possible artifacts will be identified.

We predict that strong astronomical forcing should lead to comparable results from the two cores and yield similar ratios between eccentricity, precession, and obliquity periods in keeping with predictions of celestial mechanics and other recent studies’ results for the Late Ordovician.