Cottons Breccia of King Island, Tasmania: Glacial or non-glacial, Cryogenian or Ediacaran?

Abstract

The Cottons Breccia of King Island, Tasmania, is a 100-m-thick carbonate-clast diamictite traditionally interpreted as the product of a Cryogenian or Ediacaran glaciation. It was recently reinterpreted as a mass-flow deposit, unrelated to glaciation, within an active rift basin. We reaffirm the glacial-periglacial interpretation on the basis of sedimentary facies, internal facies relations, clast lithology and isotopic composition, clast fabric analysis, and consistent stratigraphic position beneath a typical post-glacial cap dolostone. The Cumberland Creek Dolostone closely resembles basal Ediacaran cap dolostones world-wide in terms of colour, texture, sedimentary structures and isotopic characteristics. Because it was deposited above storm wave-base, differences in δ13C between closely adjacent sections suggest diachronous deposition during post-glacial marine transgression of a basin with steep local topography. This is compatible with an active rift basin in which glacigenic diamictites of the end-Cryogenian (Marinoan) pan-glacial episode were lodged. © 2009 Elsevier B.V. All rights reserved.