Paleomagnetic Constraints on Neoproterozoic ‘Snowball Earth’ Continental Reconstructions

The Neoproterozoic glacial intervals represent one of the most curious expressions of Earth’s climate. Despite the popularity of the hard “Snowball” hypothesis in the popular press, the scientific community remains divided over the extent of the Neoproterozoic glaciations, the age of the glaciations, the number of glacial events and the triggering mechanism for the glaciations. A major, and yet unresolved issue, is knowledge of the exact paleogeography during the so-called Sturtian and younger Vendian glaciations. The problem stems from the paucity of the Neoproterozoic paleomagnetic database, in particular the interval from 600-720 Ma along with the varied interpretations of those data. Here we present 4 scenarios for the paleogeographic setting in the Neoproterozoic. The first two paleogeographies are thought to be representative of the Sturtian (700-800 Ma) glaciations and the younger reconstructions represent possible extremes for the Vendian glacial events. The paleogeographies presented here have important implications for the posited triggering mechanisms for the Neoproterozoic glacials. Introduction In 1959, W.B Harland and D.E.T. Bidgood completed a paleomagnetic study of the Moelv tillite and associated sedimentary rocks in the Sparagmite district of central Norway (Harland & Bidgood, 1959). Those results, conducted without demagnetization, indicated a depositional paleolatitude of ~11 degrees. Harland and Bidgood (1959) suggested that the evidence suggested that the Precambrian glaciations were far more severe and widespread than the Phanerozoic glaciations and they further suggested that the end of these glaciations led to the explosion of life in the Cambrian. The notion of a severe ‘anti-greenhouse’ effect in the Neoproterozoic was also discussed, in seldomly cited papers, by J.D. Roberts (1971, 1976). Roberts (1971) based his arguments on the ubiquitous presence of dolomitic rocks in pre and post-glacial successions and concluded that CO2 drawdown, via carbonate sedimentation, was likely the trigger for globally synchronous glaciations in the Neoproterozoic. In 1976, Roberts expanded on the antigreenhouse concept and discussed a variety of other possible explanations for the presence of similar-age tillites on a global scale. A number of other possible