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New records of Ediacaran Acraman ejecta in drillholes from the Stuart Shelf and Officer Basin, South Australia
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
2007 (English)In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 42, no 11, 1883-1891 p.Article in journal (Refereed) Published
Abstract [en]

New occurrences of the Acraman impact ejecta layer were recently discovered in two South Australian drillholes, SCYW-79 1a (Stuart Shelf) and Munta 1 (Officer Basin) using lithostratigraphy, acritarch biostratigraphy, carbon isotope stratigraphy, and biomarker anomalies to predict the stratigraphic position. The ejecta layer is conspicuous because it consists of pink, sand-sized, angular fragments of volcanic rock distributed along the bedding plane surface of green marine siltstone. In SCYW-79 1a it forms a layer 5 mm thick; in Munta 1 the ejecta layer is thin and discontinuous because of its distance (similar to 550 km) from the impact structure. Palynological, biomarker, and carbon isotope anomalies can now be shown to coincide with the ejecta layer in SCYW-79 1a and Munta 1 suggesting the Acraman impact event may have had far reaching influences on the rapidly evolving Ediacaran biological and geochemical cycles.

Place, publisher, year, edition, pages
2007. Vol. 42, no 11, 1883-1891 p.
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-149876ISI: 000253937700004OAI: oai:DiVA.org:uu-149876DiVA: diva2:405865
Available from: 2011-03-24 Created: 2011-03-24 Last updated: 2011-07-08Bibliographically approved
In thesis
1. The Ediacaran Diversification of Organic-walled Microbiota: Ocean Life 600 Million Years Ago
Open this publication in new window or tab >>The Ediacaran Diversification of Organic-walled Microbiota: Ocean Life 600 Million Years Ago
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The only direct evidence of past life is provided by fossils. Fossils tell us about the evolution of life on Earth and they give us clues concerning ancient environments. The Ediacaran Period (roughly 635-542 million years ago) is characterised by the appearance and diversification of various microbiota and also the diversification of metazoans. Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran sedimentary successions in the Officer Basin in South Australia. Acritarch assemblages from the Giles 1 and Murnaroo 1 drillcores show a wide morphological disparity and are taxonomically diverse. Assemblages change over short stratigraphic intervals which enables the recognition of different biozones. The presence of taxa common between Australia, Siberia, Baltica and China provides a means for global correlation of the Ediacaran System. Examination of the wall ultrastructure of several acritarch specimens by use of transmission electron microscopy reveals a complexity in the cell wall that is not seen in prokaryotes but is indicative in some cases of particular clades of microalgae. Wall ultrastructures range from single-layered to three- and four-layered and from homogeneous to porous. The wall ultrastructure can be used to assess biological affinities and the affinities of the studied taxa in relation to green algae, dinoflagellates and metazoans are discussed. However, before taxonomic interpretations can be made with confidence, an understanding of taphonomic degradation of microorganisms is required. With focus on illustrated specimens, one part of this thesis explains what happens to an acritarch as it undergoes various types of degradation and why an understanding of these processes is important for taxonomic identification. A meteorite impact in South Australia spread an ejecta layer over a 550 km radius area. This ejecta layer is recognised in subsurface drillcores and provides an independent stratigraphic marker horizon that supports an acritarch-based correlation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 33 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 428
Earth sciences, acritarchs, Ediacaran, Australia, biostratigraphy, microfossils, Geovetenskap
urn:nbn:se:uu:diva-8684 (URN)978-91-554-7185-9 (ISBN)
Public defence
2008-05-16, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Available from: 2008-04-15 Created: 2008-04-15 Last updated: 2011-07-08Bibliographically approved

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