Fluctuating tidewater glaciers, chemical weathering and survival of reef-dwelling organisms: the Marinoan snowball, South Australia

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Fluctuating Tidewater Glaciers, Chemical Weathering and Survival ofReef-Dwelling Organisms: the Marinoan Snowball, South AustraliaAdam MaloofPrinceton UniversityThe snowball Earth hypothesis posits that the oceans were sealed in ice for millions of years, at least once or twice, between 720 and 635 million years ago. However, three observations have caused some to question this backbone of the snowball Earth hypothesis: (1) There is geological evidence for dynamic wet-based glaciers, in the form of thick glacially derived sediments and deep glacial erosion. How was sufficient snow delivered to ice sheets to keep them flowing when the oceans were covered in ice? (2) There is geological and geochemical evidence for thermal episodicity during a single snowball interval in the form of interbedded glacial and non-glacial sediments. How would ice advance and retreat and how would variable temperature/humidity conditions develop on a deeply frozen Earth with ice-covered oceans? (3) Photosynthesizing eukaryotes appear to survive the glaciation, unscathed. How did photosynthesizers survive millions of years of freezing conditions in isolated refugia without having a major influence on the course of evolutionary biology? The Marinoan (ended 635 Ma) glacial succession of South Australia (SA) contains the most reliable paleomagnetic evidence for equatorial sedimentation of any Neoproterozoic glacial deposit worldwide. Additionally, the Flinders and Gammons ranges of SA boast superb outcrop for hundreds of kilometers along and across paleo-shoreline strike, allowing for detailed reconstruction of sedimentary environments and lateral chemical and isotopic gradients, all in the context of 3-dimensional stratigraphy and basin analysis. With the possible exception of northern Namibia, nowhere else in the world provides such an opportunity to study the sedimentary and geochemical record of Neoproterozoic glaciation. The proposed study will document the Marinoan low-latitude glaciation in South Australia through a multidisciplinary study of the pre-, syn- and post-glacial deposits exposed in the Flinders and Gammon Ranges. Our work will evaluate the intensity of the hydrological cycle, the thermal regime of equatorial glaciers, and the evidence that multicellular life predated and survived a snowball Earth episode.