Astrochronology Of The Early–middle Ordovician And Late Devonian In China And Astronomical Forced Paleoclimate Change

Earth's marine life had experienced five mass extinctions and three significant radiations in the Phanerozoic Eon,including the famous Great Ordovician Biodiversification event(GOBE)and Late Devonian Frasnian–Famennian(F–F)mass extinction.A high-resolution time framework for the Ordovician and Late Devonian is the key to understand these geological events.Astronomical-forcing signals embedded in cyclostratigraphy can be exploited as a geochronometer and provide an alternative method to improve geochronology.A high-resolution(0.02–0.4 myr)astronomical time scale can be established once the Milankovitch cycles are recognized in well-preserved stratigraphic successions.In this study,based on the eight Lower–Middle Ordovician and Upper Devonian sections in North China,South China and West Junggar,we focus on the Early–Middle Ordovician biodiversification event and Late Devonian F–F mass extinction.Systematic cyclostratigraphy is carried out based on the variety of paleoclimate proxies(e.g.magnetic susceptibility,geochemistry of element,and gamma ray).According to the characteristics of paleoclimate and paleo-environment changes in the Early-Middle Ordovician and Late Devonian,we propose that astronomical-forcing plays an important role of the major bio-environmental events in geological history.