Age constraints on Precambrian glaciations and the subdivision of Neoproterozoic time

Abstract

A review of age constraints on the Neoproterozoic glaciations suggests that at least four distinct glacial events can be recognised, three of which appear to be global. These are (in order from oldest to youngest) the Kaigas (poorly constrained to between 770 and 735 Ma), Sturtian (well constrained to c. 715 - 680 Ma), Marinoan (well constrained to 660 - c. 635 Ma), and Gaskiers (extremely well constrained to c. 585 - c. 582 Ma). Excellent correspondence of some U-Pb dates suggests that these glaciations may be of practical use in global chronostratigraphy, a principle previously recognised by the IUGS Terminal Neoproterozoic Subcommission in the placement of the GSSP for the base of the Ediacaran System at the base of a Marinoan “cap carbonate”. It is here suggested that the newly constituted IUGS Ediacaran Subcommission follow this principle by searching for appropriate sites and horizons to place GSSPs (a) for the base of the Upper Series of the Ediacaran System (for which the name Vendian is suggested) immediately above a “Gaskiers” diamictite, (b) for the base of the Upper Series of the Cryogenian System at the base of a “Sturtian” diamictite, and (c) for the base of the Cryogenian System at a level between the top of the “Kaigas” diamictites, and the base of the “Sturtian” diamictites. This would confine the four glaciations and the subsequent rise of metazoans to a separate Series each, and combines the two greatest glaciations in Earth history, the Sturtian and Marinoan glaciations, as the Cryogenian System. While there may be reasons to consider other names, the widespread use of the names “Sturtian” and “Marinoan” in the literature suggests the Subcommission should consider these names for the Lower and Upper Series of the Cryogenian respectively.