Colloquium: Catherine Rose

Catherine Rose

Steve Fossett Postdoctoral Fellow, Department of Earth and Planetary Sciences, Washington University in St. Louis

Abstract: The Neoproterozoic Era was punctuated by the `Sturtian' (~710 million years ago) and `Marinoan' (~635 million years ago) low-latitude glaciations. Carbonates preceding the younger Marinoan glacial succession record an ~18‰ negative shift in the δ¹³C of carbonate around the world. This `Trezona' isotopic anomaly is the largest δ¹³C shift in Earth history and its origin and timing remain controversial. The δ¹³C 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 δ¹³C anomaly might record secondary alteration by percolating fluids following carbonate deposition. Here we document dropstones within the carbonate platform sediments immediately below the Marinoan glacial diamictite in South Australia. Advancing ice sheets caused soft-sediment deformation of the beds below the glacial diamictite, as well as subglacial erosion of carbonates containing the recovery from the Trezona negative δ¹³C anomaly. These stratigraphic relationships require that the nadir of the Trezona δ¹³C anomaly was recorded prior to local glacier advance and long before late-stage burial diagenesis could have occurred, and that δ¹³C recovery toward 0‰ was synchronous with the appearance of icebergs in the tropics.