| Summary: | [1] Between 1000 and 542 million years ago, the geologic record shows evidence for the progressive rise in atmospheric oxygen, large changes in the carbon cycle, and extreme climatic states. This era was punctuated by the `Sturtian' (710 million years ago) and `Marinoan' (635 million years ago) glaciations, where ice may have extended to low-latitudes near the equator. These glaciations are of particular importance because their severity may have set the stage for the radiation of complex animal life. In the pages that follow, I use a combination of field observations and chemostratigraphic data to study sedimentary rocks in South Australia that document the comings and goings of the younger Marinoan ice-sheet near the paleo-equator. This research yields new insights into the origin of pre-glacial perturbations to the carbon cycle (Chapter 2), the nature of syn-glacial incision and deposition (Chapter 3), and the style of subsequent deglaciation (Chapter 4). [2] Carbonates preceding the Marinoan glacial succession record an 18 permil negative shift in the d13C of carbonate around the world. This `Trezona' isotopic anomaly is the largest d13C shift in Earth history and its origin and timing with respect to the glaciation remain controversial. The d13C anomaly could record a dramatic reorganization of Earth's carbon cycle and be linked causally to the initiation of Marinoan ice-house conditions. Alternatively, the d13C anomaly might record secondary fluid alteration following carbonate deposition. I present detailed sedimentological observations paired with chemostratigraphic data to show that the Trezona anomaly was recorded prior to the local glacier advance and late-stage burial diagenesis, and that d13C recovery toward 0 permil was synchronous with the appearance of icebergs in the tropics. This work provides the first systematic assessment of all the competing hypotheses offered to explain the Trezona d13C anomaly. [3] Glacial deposits generated during the Marinoan Glaciation have received little attention in ...
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