Tracking variable sedimentation rates and astronomical forcing in Phanerozoic paleoclimate proxy series with evolutionary correlation coefficients and hypothesis testing

This paper addresses two fundamental issues in cyclostratigraphy and paleoclimatology: identification of astronomical forcing in sequences of stratigraphic cycles, and accurate evaluation of variable sedimentation rates. The technique presented here considers these issues part of an inverse problem and estimates the product-moment correlation coefficient between the power spectra of astronomical solutions and paleoclimate proxy series across a range of test sedimentation rates. The number of contributing astronomical parameters in the estimate is also considered. Our estimation procedure tests the hypothesis that astronomical forcing had a significant impact on proxy records. The null hypothesis of no astronomical forcing is evaluated using a Monte Carlo simulation approach. The test is applied using a sliding stratigraphic window to track variable sedimentation rates along the paleoclimate proxy series, in a procedure termed “eCOCO” (evolutionary correlation coefficient) analysis. Representative models with constant and variable sedimentation rates, and pure noise and mixed signal and noise series are evaluated to demonstrate the robustness of the approach. The method is then applied to Cenozoic, Mesozoic and Paleozoic paleoclimate series. The Cenozoic case study focuses on a high-resolution Paleocene-Eocene iron concentration series from ODP Site 1262 (Leg 208) covering the Paleocene-Eocene Thermal Maximum and Eocene Thermal Maximum 2 events. The eCOCO time-calibrated iron series confirms previous findings of a role for long-term astronomical forcing of these Eocene events. The Mesozoic case study applies eCOCO to the classic Late Triassic Newark depth rank series of eastern North America. The estimated high-resolution sedimentation rate map in this case demonstrates a causal link between variations in depositional environment and sedimentation rate. Finally, the Paleozoic case study supports the cyclostratigraphic interpretation of a Devonian magnetic susceptibility series at La Thure, Belgium and provides new insights into changes of the depositional setting at this location. Taken together, eCOCO is a powerful tool for simultaneously evaluating sedimentation rates and astronomical forcing for paleoclimate series throughout the Phanerozoic.