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 319320, no. 0 (2/15/ 2012): 241-50.


Author: M. H. Monroe
Last updated 29/05/2013
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