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Neoproterozoic subdivision in Australia
Geological Survey of Western Australia, Department of Industry and Resources.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Palaeobiology. Paleobiologi.
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences, Palaeobiology. Paleobiologi.
Mineral Resources Tasmania, Australia.
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2005 (English)In: Central Australian Basins Symposium: Petroleum and Mineral Potential, 2005Conference paper (Other scientific)
Abstract [en]

Neoproterozoic subdivision is well advanced in Australia using integrated results from lithostratigraphy, palynology, isotope chemostratigraphy and stromatolite biostratigraphy. Previously proposed Cryogenian correlations were tested by the drilling of GSWA Lancer-1 in the western Officer Basin and were found to be reliable. The consistency of the results allows the succession to be tied to limited geochronological ages from the Adelaide Rift Complex. Data are still sparse on the interval between the Sturtian and Marinoan glaciations, but good correlations exist in the Ediacaran.

The base of the cap carbonate in Enorama Creek in the Adelaide Rift Complex has been ratified as the Global Stratotype Section and Point (GSSP) for the newly defined Ediacaran System and Period. The Flinders Ranges have a near-continuous section from the Marinoan glaciation to the Cambrian boundary, especially around the Brachina and Bunyeroo gorges. Lithostratigraphy, and local and regional correlations are well established, including links between the type sections, measured sections throughout the Adelaide Rift Complex and continuously cored drillhole sections on the Stuart Shelf, 80–100 km to the northeast, and to the Officer and Amadeus basins. An integrated approach, using lithostratigraphy; stratigraphic markers (glacial episodes, the time-synchronous Acraman impact ejecta layer, canyon cutting); carbon isotope chemostratigraphy; sequence stratigraphy; seismic interpretation; stromatolite biostratigraphy; and the first appearance of bilaterians and associated trace fossils, has proved successful.

Acritarchs are acid-insoluble fossils of single-celled, phytoplanktonic green algae and are ideal for zonation. A rigorous sampling program began in 1991 to establish an acritarch biostratigraphy throughout Australian Neoproterozoic basins, based on palynological studies of continuously cored drillholes. Extensive field sampling of sections in the Flinders Ranges was unsuccessful, partly because the rift succession is too thermally mature for palynomorphs to be preserved, and partly because organic material has been leached from a deeply weathered profile. No identifiable acritarchs were recovered from this area, or from outcrops in other basins. However, Stuart Shelf drillholes contain well-preserved palynomorphs, although preservation is patchy in parts of the succession. Nevertheless, there are enough data for correlation with excellently preserved assemblages from the Officer and Amadeus basins. Georgina Basin preservation is too poor for useful analysis at present. Data from the Officer and Amadeus basins demonstrate the potential for biostratigraphic zonation in the lower and middle Ediacaran. Biostratigraphic correlation parallels correlations based on organic carbon isotope curves.

Middle Ediacaran acritarch assemblages are extraordinarily diverse taxonomically, morphologically complex, and show typical patterns of secular diversity. These characteristics are ideal for the development of a zonal scheme, with levels of precision equivalent to the Phanerozoic record. The zones are independent of taphonomic and palaeoenvironmental influences, and they are demonstrably independent of lithology, lithostratigraphy, and sequence stratigraphy. Using composite sections, two palynofloras, the Ediacaran Leiosphere Palynoflora (ELP) and the Ediacaran Complex Acanthomorph Palynoflora (ECAP), have been recognised. The ECAP has been subdivided into four zones. The scheme is preliminary, but represents a significant advance in Neoproterozoic biostratigraphic studies, and should provide an important tool for future stratigraphic correlation. Additional studies are in progress to refine the correlations by examining undocumented parts of the succession, especially from Murnaroo-1 and Giles-1. The presence of certain acritarch species in probably coeval successions in Australia, Siberia, China, and northern Europe, suggests that the proposed zonation has good potential for global application, and that biostratigraphic principles and methodology can be applied to the Neoproterozoic.

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URN: urn:nbn:se:uu:diva-83167OAI: oai:DiVA.org:uu-83167DiVA: diva2:111074
Available from: 2006-10-23 Created: 2006-10-23

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Willman, SebastianMoczydlowska, Malgorzata
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