Ordovician cyclostratigraphy and astrochronology

Abstract Cyclostratigraphy is an important tool for understanding astronomical climate forcing and for reconstructing geological time in sedimentary sequences, provided that an imprint of insolation variations caused by Earth's orbital eccentricity, obliquity and precession is preserved (Milankovitch forcing). Understanding astronomical climate forcing has proven fundamental for the study of Cenozoic climate systems and the construction of high-resolution continuous time scales (astrochronologies). Pre-Cenozoic astrochronologies face several challenges: (1) uncertainties in the deep-time astronomical solutions and parameters; (2) less complete and less well preserved strata; and (3) the sparsity of geochronologic anchor points. Consequently, Paleozoic astrochronologies are typically based on identification of the stable 405 kyr eccentricity cycle instead of shorter astronomical cycles. Here, a state-of-the-art review of Ordovician cyclostratigraphy and astrochronology is presented, as well as suggestions on their robust application in an Ordovician context. Ordovician astronomically driven climate dynamics are suggested to have influenced processes like glacial dynamics, sea-level variations and changes in biodiversity. Ordovician cyclostratigraphic studies can help to construct high-resolution numerical time scales, ideally in combination with high-quality radio-isotopic dating. As such, cyclostratigraphy is becoming an increasingly important part of an integrated stratigraphic approach to help disentangle Ordovician stratigraphy and palaeoenviromental changes.