Update on the “Snowball”

Two recent papers add weight to the “against” view expressed in For and against “Snowball Earth in EPN of October 2004”  One gives age of 709±5 Ma for tuff immediately beneath a supposed Sturtian diamictite from the western USA (Fanning, C.M & Link, P.K. 2004.  U-Pb SHRIMP ages of Neoproterozoic (Sturtian) glaciogenic Pocatello Formation, southeastern Idaho.  Geology, v. 32, p. 881-884), which does not tally with the radiometric age (685 Ma) of similar rocks not far away.  The other (Calver, C.R. et al. 2004.  U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania. Geology, v. 32, p. 893-896), gives a 575±3 Ma age for sills intruding a “Marinoan” diamictite in Tasmana, and 582±4 Ma for a rhyodacite immediately beneath it.  This suggests that these antipodean glaciogenic rocks are correlative with those in Newfoundland and Norway, that are supposedly representatives of the Varangerian glacial epoch.  Yet the authors are pains to state that the Marinoan and the Varangerian are one and the same.  Read these papers if you are still confused!

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