NEW RE-OS AGE CONSTRAINTS AND OS ISOTOPE DATA FROM THE NEOPROTEROZOIC OF MONGOLIA: IMPLICATIONS FOR GLACIATIONS, PALEOWEATHERING FLUXES AND COMPLEX LIFE

The ca. 717-539 Ma Cryogenian and Ediacaran periods hosted a suite of unprecedented geologic and geobiological events including supercontinent reorganization, large carbon isotope excursions, Snowball Earth glaciations, and the evolution of complex life. Neoproterozoic sedimentary strata from the Zavkhan and Khuvsgul terranes, Mongolia, are replete with evidence for two Cryogenian glaciations, multiple carbon isotope excursions (CIEs)—specifically the Taishir and BACE CIEs—and enigmatic microfossil assemblages similar to those described from Neoproterozoic strata globally. These characteristics make Mongolia ideal for integrated biogeochemical and geobiological investigation through this interval of Earth history. However, a present paucity of radioisotopic age constraints from Mongolian sedimentary strata hinders 1) attempts to integrate Mongolian records with global archives, and 2) efforts to assess the global extent of geobiological and paleoenvironmental change through the mid- to late-Neoproterozoic.

Here, we present new Re-Os radioisotopic ages and Os isotope data from organic-rich shale and micritic limestone horizons spanning the Zavkhan and Khuvsgul terranes, Mongolia. These depositional ages, combined with sedimentological and paleontological data, will help calibrate a valuable temporal framework for Cryogenian glacial deposits and Ediacaran fossiliferous horizons in Mongolia. Additionally, Os isotope data allows us to assess the nature and degree of chemical and/or physical weathering across this interval, with implications for ocean nutrient supply and the evolution of complex life.