Australia: The Land Where Time Began

A biography of the Australian continent 

The Trezona delta-13C Anomaly Beneath the Glaciation of the End-Cryogenian - Constraints of the Origin and Relative Timing

Low-latitude glaciations at about 710 Ma, the Sturtian Glaciation and about 635 Ma, the Marinoan Glaciation, which were low-latitude glaciations, punctuated the Neoproterozoic Era. A negative shift, of about 18‰, in the δ¹³C of worldwide carbonate is recorded preceding the Marinoan Glaciation succession, the younger of the 2 glacial episodes. The origins and timing of the Trezona Isotopic Anomaly is the largest known δ¹³C shift in the history of the Earth, and its origin and timing remain controversial. The authors¹ suggest a dramatic reorganisation of the carbon cycle of the Earth could be recorded by the δ¹³C anomaly, which could be causally linked to the initiation of the icehouse conditions of the Marinoan  Glaciation, though the δ¹³C could alternatively record a secondary fluid alteration which followed the deposition of the carbonate. In this paper the authors¹ document dropstones within carbonate sediments that have been found immediately beneath the glacial diamictites from the Marinoan Glaciation in South Australia. Soft-sediment deformation of the beds underlying the diamictites, as well as subglacial erosion of the carbonate beneath the ice, that was caused by advancing ice sheets, indicating that the  δ¹³C values must have been acquired prior to the glaciation. These stratigraphic relationships require the nadir of the Trezona δ¹³C anomaly to be recorded before the local glacier advance, and long before late-stage burial could have taken place, though they don't provide a specific mechanism that could explain the Trezona δ¹³C anomaly. In the Trezona Formation the recovery of the δ¹³C anomaly towards 0‰ was synchronous with the appearance in the tropics of icebergs.

Sources & Further reading

1. Rose, Catherine V., Nicholas L. Swanson-Hysell, Jon M. Husson, Laura N. Poppick, John M. Cottle, Blair Schoene, and Adam C. Maloof. "Constraints on the Origin and Relative Timing of the Trezona Δ13c Anomaly Below the End-Cryogenian Glaciation." Earth and Planetary Science Letters 319–320, no. 0 (2/15/ 2012): 241-50.