ABSTRACT:

The prevalent yet controversial Snowball Earth hypothesis proposes an Earth almost completely covered in ice at least twice during Neoproterozoic time (ca. 800-542 Ma). This hypothesis predicts the formation of lithologically and isotopically unique ³cap carbonate sequences,² precipitated from the oceans nearly instantaneously after these extreme glaciations, and paving the way for the subsequent rise of metazoans. Evaluation of the hypothesis is difficult due to the lack of geochronologic control to demonstrate synchroneity of these proposed global events.  Here I review new research on the stratigraphic record of this time in Utah and Idaho. Results are generally consistent with a low-latitude glacial interpretation, yet systematic U-Pb geochronology on detrital zircons and detailed sedimentology/stable isotope geochemistry of the local cap carbonate interval challenge the hypothesis on several fronts. Potential implications include 1) evidence for three, not two, Snowball events; 2) protracted glaciation (no Snowball); 3) the inability to use cap carbonates as simple time markers; and 4) the revision of the GSSP at the base of the Ediacaran Period (635 Ma).