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Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
2007 (English)In: Lethaia: an international journal of palaeontology and stratigraphy, ISSN 0024-1164, E-ISSN 1502-3931, Vol. 40, no 2, 111-123 p.Article in journal (Refereed) Published
Abstract [en]

Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran deposits in the Officer Basin in Australia. The assemblages are taxonomically diverse, change over short stratigraphical intervals and are largely facies independent across marine basins. Affinities of this informal group of fossils to modern biota are poorly recognized or unknown, with the exception of only a few taxa. Morphological studies by use of transmitted light microscopy, geochemical analyses and other lines of evidence, suggest that some Precambrian acritarchs are related to algae (including prasinophytes, chlorophytes, and perhaps also dinoflagellates). Limitations in magnification and resolution using transmitted light microscopy may be relevant when assessing relationships to modern taxa. Scanning electron microscopy reveals details of morphology, microstructure and wall surface microelements, whereas transmission electron microscopy provides high-resolution images of the cell wall ultrastructure. In the light of previous ultrastructural studies it can be concluded that the division of acritarchs into leiospheres (unornamented) and acanthomorphs (ornamented) is entirely artificial and has no phylogenetic meaning. Examination of Gyalosphaeridium pulchrum using transmission electron microscopy reveals a vesicle wall with four distinct layers. This multilayered wall ultrastructure is broadly shared by a range of morphologically diverse acritarchs as well as some extant microalgae. The chemically resistant biopolymers forming the comparatively thick cell, together with the overall morphology support the interpretation of the microfossil as being in the resting stage in the life cycle. The set of features, morphological and ultrastructural, suggests closer relationship to green algae than dinoflagellates.

Place, publisher, year, edition, pages
2007. Vol. 40, no 2, 111-123 p.
Keyword [en]
Acritarchs, Australia, Ediacaran, Neoproterozoic, Officer Basin, phytoplankton, protists, TEM, wall ultrastructure
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97150DOI: 10.1111/j.1502-3931.2007.00023.xISI: 000246623900002OAI: oai:DiVA.org:uu-97150DiVA: diva2:171960
Available from: 2008-04-15 Created: 2008-04-15 Last updated: 2011-02-01Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 428
Keyword
Earth sciences, acritarchs, Ediacaran, Australia, biostratigraphy, microfossils, Geovetenskap
Identifiers
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
Opponent
Supervisors
Available from: 2008-04-15 Created: 2008-04-15 Last updated: 2011-07-08Bibliographically approved

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Willman, SebastianMoczydłowska, Małgorzata

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