Collaborative Research: The Aftermath of a Snowball Earth

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An investigation of the unique set of environmental conditions attending the aftermath of a Neoproterozoic "snowball" Earth will be undertaken. It is hypothesized that a series of glaciations occurred 750-570 million years ago that were so severe that the oceans froze over to the equator. These glaciations ended violently under ultra-greenhouse conditions (required to overcome the high ice albedo), brought about by the slow buildup of CO2 by subaerial volcanic outgassing in the absence of sinks for C. Intense silicate weathering must have followed deglaciation, driven by high surface temperatures, carbonic acid rain, and frost-shattered bedrock including unaltered volcanic material accumulated during the prolonged snowball period. The weathering reactions would have taken up the excess CO2 and delivered cations and bicarbonate to the oceans, driving massive and rapid precipitation of "cap" dolomites and limestones, which are widely observed overlying Neoproterozoic glacial deposits. The following studies of selected cap dolomites and limestones in Namibia, Mauritania, Australia and China will be carried out: (1) Radiogenic Sr isotopic anomalies will be sought which would record the input of riverine Sr to the surface ocean at a time when ocean mixing would have been impeded by high surface temperatures and low density glacial meltwater, (2) U-Pb dating of cap dolomites will be attempted, given evidence that the dolomites are primary and result from high Mg/Ca riverine input due to rapid weathering of mafic volcanic material; (3) Subsidence histories of cap carbonate sequences will be studied as a means of estimating the duration of snowball periods; (4) Collections of cap carbonates and associated terrigenous sediments will be made for the purpose of investigating the turnover of acritarch assemblages coincident with snowball events. These studies will be used to test the validity and our understanding of the snowball Earth hypothesis, which if true connotes the most extreme climates and climate changes in Earth history.