1 U-Pb zircon (CA-ID-TIMS) age supports globally synchronous Sturtian deglaciation Grant M. Cox 1* , Vincent Isakson 2 , Paul F. Hoffman 3 , Thomas M. Gernon 4 , Mark D. Schmitz 2 , Sameh Shahin 1 , Alan S. Collins 1 , Wolfgang Preiss 1 , Morgan L. Blades 1 , Ross N. Mitchell 5 , Adam Nordsvan 5 1. Centre for Tectonics, Resources and Exploration (TraX), Department of Earth Sciences, The University of Adelaide, Adelaide, SA 5005, Australia. 2. Department of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho. 3. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA. 4. Ocean and Earth Science, University of Southampton, European Way, Southampton SO14 3ZH, UK. 5. Department of Applied Geology, Curtin University, Bentley, Western Australia 6845, Australia * Corresponding author: grant.cox@adelaide.edu.au Abstract A central prediction of the Snowball Earth hypothesis is that glacial onset should be synchronous at low latitudes, and its termination should be rapid and synchronous globally. High precision U/Pb zircon ages provide supporting evidence for the synchronous onset (within error) of the Sturtian glaciation (ca. 716 Ma) on multiple continents. Successful application of Re-Os techniques on organic rich shales and carbonates allow for the possibility of a globally synchronous Sturtian deglaciation (ca. 660 Ma), but the sparse isotopic age constraints leave this open to debate. Here we report the first high precision U-Pb zircon age of 663.03  0.11 Ma (2) for the end Sturtian recorded in the Bolla Bollana Formation of South Australia. This age supports previously published ages and is permissive with a globally synchronous deglaciation. In conjunction with the timing of glacial onset, this age reinforces the ca. 58 Myr duration of the Sturtian Snowball. Keywords: Snowball Earth, Sturtian, Synchronous Deglaciation, CA-ID-TIMS Introduction Some of the most extreme climate episodes the Earth has experienced occurred during a protracted phase of near-global glaciations in the Cryogenian period (720-635 Ma). These “Snowball” glaciations (Hoffman et al., 1998; Kirschvink, 1992), or cryochrons (Hoffman et al., 2017) are evidenced by the wide distribution of glacial deposits, particularly those associated with carbonate platforms, with the implication that glaciers entered the marine realm