The evaluation of eccentricity-related amplitude modulation and bundling in paleoclimate data: An inverse approach for astrochronologic testing and time scale optimization

Cyclostratigraphic analysis has produced fundamental advancements in our understanding of climate change, paleoceanography, celestial mechanics, geochronology, and chronostratigraphy. Of central importance to this success has been the development of astrochronologic testing methods for the evaluation of astronomical-climate influence on sedimentation. Most pre-Pleistocene astrochronologic testing methods fall into one of two categories: (1) those that test for expected amplitude or frequency modulation imposed by an astronomical signal or (2) those that test for bedding hierarchies (frequency ratios or bundling) that are predicted by the dominant astronomical periods. In this study, a statistical methodology for combining these complementary approaches is developed, which identifies the time scale that simultaneously optimizes eccentricity amplitude modulation of the precession band, and the concentration of power at precession (carrier) and eccentricity (modulator) frequencies. The technique is demonstrated to have high statistical power—it is capable of identifying astronomical cycles when present—under a wide range of conditions, and its application to synthetic models illuminates a range of potential pitfalls that are encountered when more conventional nonoptimization approaches are used. The method is also independent from the interpretation of power spectrum peak significance, resolving previous concerns regarding appropriate confidence level assessment and “multiple testing.” As two case studies, the algorithm is applied to Miocene strata of Ocean Drilling Program (ODP) Site 926B, and the Paleocene-Eocene Thermal Maximum-Eocene Thermal Maximum 2 interval at ODP Site 1262. The results verify published cyclostratigraphic interpretations and support the theoretical astronomical solutions. This new astrochronologic testing approach can be used to evaluate cyclostratigraphic records spanning the Phanerozoic and potentially beyond.