Astrochronologic Testing in Deep-Time Strata: Historical Overview and Recent Advances

Abstract:

The quest for astronomical-climate rhythms (“Milankovitch cycles”) in Phanerozoic strata is now commonplace, and has yielded fundamental advancements in our understanding of climate change, paleoceanography, astrodynamics, 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; this can be especially challenging for deep-time strata that lack sufficient independent time control (e.g., radioisotopic data) to unambiguously calibrate observed spatial rhythms to temporal periods. Most deep-time (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") that are predicted by the dominant astronomical periods. In this talk, I discuss the historical context of these methods, recent advances that overcome subjective evaluation and circular reasoning, and their implementation in a new “open source” software package for astrochronology (Meyers, 2014, astrochron: An R Package for Astrochronology).