MILANKOVITCH-SCALE GLACIO-EUSTASY RECORDED IN STRATIGRAPHY AND ITS RISING INFLUENCE IN 21ST CENTURY GEOSCIENCE

Meter-scale cyclicity in shallow-marine stratigraphy—or cyclostratigraphy—has long captivated the sedimentology community. Typical repetitive shallowing-upward sediment deposition in platform settings suggests forcing from glacio-eustatic oscillations controlled by Milankovitch cycles. Depositional stacking patterns in greenhouse versus icehouse worlds indicate unique glacio-eustatic signatures. The “third order” cycles of sequence stratigraphy are now understood to be records of long-period Milankovitch cycles. A selection of Precambrian and Phanerozoic formations will be presented to illustrate the variety of glacio-eustatic depositional cycles that have been observed through geologic time.

The importance of shallow marine cyclostratigraphy in 21st century geoscience relates to the development of the Milankovitch-based "Astronomical Time Scale" for Earth history. The Geologic Time Scale 2012 for the Cenozoic and late Mesozoic is calibrated by high-resolution Milankovitch cycles identified in deep-sea sediment derived from marine phytoplankton. By contrast, pre-Jurassic deep-sea sediment prior to the evolution of marine phytoplankton originates from the shallow shelf and near-shore, governed in large part by sea level changes. This has curtailed the reconstruction of Milankovitch cycle sequences from pre-Jurassic marine stratigraphy. Shallow-marine depositional systems are the next research frontier for understanding Milankovitch cycles in pre-Jurassic stratigraphy. This research, which is ongoing and robust with sophisticated analysis and modeling tools at hand, is poised to transform our understanding of ancient glacio-eustasy and climate change, and will extend the Astronomical Time Scale into the Precambrian.