Were Ediacaran siliciclastics of South Australia coastal or deep marine?
Version of Record online: 17 JAN 2012
© 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists
Volume 59, Issue 4, pages 1208–1236, June 2012
How to Cite
RETALLACK, G. J. (2012), Were Ediacaran siliciclastics of South Australia coastal or deep marine?. Sedimentology, 59: 1208–1236. doi: 10.1111/j.1365-3091.2011.01302.x
- Issue online: 16 MAY 2012
- Version of Record online: 17 JAN 2012
- Accepted manuscript online: 17 OCT 2011 10:49AM EST
- Manuscript received 18 April 2011; revision accepted 11 October 2011
- South Australia
The Late Neoproterozoic Ediacara Member of the Rawnsley Quartzite in South Australia has been considered aeolian, fluvial, intertidal and deep marine by various authors. Palaeosols would not be expected for the deep marine interpretation, but some palaeosols should be evident for the aeolian–fluvial–intertidal interpretations, and this is the first study to examine the Ediacara Member at a petrographic and geochemical scale appropriate to recognize potential palaeosols. Recognition of palaeosols and floodplain facies in Neoproterozoic rocks is a challenge because such rocks are too ancient for diagnostic non-marine fossils such as root traces. The varied thickness of Ediacara Member red siltstones and white sandstones is distinct from laterally persistent overlying and underlying grey shales and limestones with acritarchs, stromatolites and other marine fossils. The sandstones are trough cross-bedded and fill palaeovalleys. The red siltstones have poorly sorted, highly angular, silt-size grains characteristic of loess. Particular sandy and silty beds were sampled for detailed petrographic and geochemical studies, because they include desiccation cracks, sand crystals, ice cracks, carbonate nodules and soft-sediment deformation like those of palaeosols. Chemical and grain-size variations within these beds reveal surficial clay formation and oxidation from feldspar as in soils. Petrographic studies also revealed surficial disruption of these palaeosols by filamentous structures comparable with microbial ropes of biological soil crusts. This array of palaeosol features may be of use for recognizing palaeosols in other Neoproterozoic siliciclastic sequences.