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The Ediacaran Diversification of Organic-Walled Microbiota Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 428 The Ediacaran Diversification of Organic-walled Microbiota Ocean Life 600 Million Years Ago SEBASTIAN WILLMAN ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 UPPSALA ISBN 978-91-554-7185-9 2008 urn:nbn:se:uu:diva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ill min familj List of publications I Willman S, Moczydowska M, Grey K (2006) Neoprotero- zoic (Ediacaran) diversification of acritarchs – A new record from the Murnaroo 1 drillcore, eastern Officer Basin, Austra- lia. Review of Palaeobotany and Palynology 139, 17–39. II Willman S, Moczydowska M (2008) Ediacaran acritarch biota from the Giles 1 drillhole, Officer Basin, Australia, and its potential for biostratigraphic correlation. Precambrian Re- search 162, 498–530. III Willman S (accepted) Acritarchs and their potential in Edia- caran biostratigraphy – Examples from the Officer Basin, Australia. Comunicações Geológicas, 14 pp. IV Willman S, Moczydowska M (2007) Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia. Le- thaia 40, 111–123. V Willman S (manuscript) Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Edia- caran of Australia. Submitted to Geobiology, 15 pp. VI Grey K, Willman S (accepted) Taphonomy of Ediacaran acritarchs from Australia: significance for taxonomy and bio- stratigraphy. PALAIOS, 30 pp. VII Hill AC, Haines PW, Grey K, Willman S (2007) New records of Ediacaran Acraman ejecta in drillholes from the Stuart Shelf and Officer Basin, South Australia. Meteoritics & Planetary Science 42, 1883–1891. Additionally, the following paper was written during my studies at Uppsala University, but is not included in this thesis: VIII Willman S (2007) Testing the role of spines as predatory defense. Journal of Shellfish Research 26, 261–266. Reproduction of the published papers is made with kind permission from the copyright holders. Paper I and II © Elsevier Paper III © by the author Paper IV © Wiley-Blackwell Publishing Ltd. Paper V © by the author Paper VI © by the authors Paper VII © Meteoritical Society Paper VIII © National Shellfisheries Association/Journal of Shellfish Re- search Statement of authorship Paper I and II: S. Willman analysed the material and interpreted the results, shared writing. Paper III: S. Willman wrote the manuscript. Paper IV: S. Willman performed the experimental part and analysed the material, shared writing. Paper V: S. Willman performed the analysis and wrote the manu- script. Paper VI: S. Willman helped in interpretations, shared writing. Paper VII: S. Willman assisted in data collection and writing. Front cover: Tanarium pluriprotensum, an Ediacaran age acritarch from the Giles 1 drillcore, Officer Basin, South Australia. Contents List of publications ...................................................................................... vii 1. Introduction ............................................................................................... 13 Aims and introduction to the studies ........................................................ 13 The Precambrian – life evolves, the environment changes ...................... 14 The Ediacaran Period ............................................................................... 16 What is an acritarch? ................................................................................ 18 2. Ediacaran organic-walled microbiota from Australia ............................... 21 New records and the potential for biostratigraphy ................................... 22 Wall ultrastructure and biological affinities ............................................. 23 Life after death: the degradation of acritarchs and its consequences ....... 25 New records of the Acraman impact ejecta layer and its importance ...... 25 3. Svensk sammanfattning ............................................................................ 26 Istiderna .................................................................................................... 26 Meteoritnedslaget ..................................................................................... 26 Min forskning ........................................................................................... 27 4. Acknowledgements ................................................................................... 29 5. References ................................................................................................. 31 12 1. Introduction Aims and introduction to the studies Ediacaran fossils document a most remarkable palaeobiological and evolu- tionary event that includes the origin and diversification of a variety of mi- croorganisms and metazoans. Among these, organic-walled microbiota of unknown affinities form an integral part of the biosphere. What was life in the oceans like between 600 and 550 million years (Ma) ago? What kind of organisms populated coastal and marine environments? These are some questions that I address in this thesis. I studied organic-walled microfossils of Ediacaran age (~635-542 Ma) recovered from subsurface rock- successions in South Australia (Figure 1). Organic-walled microfossils, es- pecially those referred to as acritarchs, are common, widespread and mor- phologically distinguishable in these rocks and are therefore ideal objects to study when addressing the questions posed above. The thesis consists of three thematic parts: (1) documentation of the morphological disparity and taxonomic diversity of the microbiota, interpretation of its diversification through time with regards to environmental change, and applying this to biostratigraphy and correlation of rock successions on both a local and global scale (2) investigation of the biological affinities of selected acritarchs by examining their wall ultrastructure by use of transmission electron mi- croscopy, and to infer their relationship to modern biota (3) study effects of the post-mortem degradation of individual acritarchs on taxonomic interpre- tation and what further implications this has on stratigraphic correlation and subdivision. In addition, the thesis consists of a report on the discovery of the Acraman impact ejecta layer in two drillcores and shows how this marker level can be used to confidently correlate geological successions. Acritarchs have been studied from sedimentary successions worldwide for more than a century. Although many studies have focused on Ediacaran assemblages, research is still in an early phase and in need of sub- stantial work. South Australia has proved to be a key area, alongside China, Siberia and Baltica, in studies of Ediacaran organic-walled microfossils. It is likely that the fossils from these areas will help to solve many purely palaeo- biological problems. The real challenge, however, lies in tying the diversifi- cation of the microbiota to environmental change, such as the rise of oxygen, to the subsequent emergence of metazoans and the explosion of diverse life- forms in the Cambrian (e.g. McFadden et al. 2008). From an applied per- spective, acritarchs appear to be important for biostratigraphic subdivision of 13 the late Neoproterozoic. The increased interest in Neoproterozoic rocks as a potential source of fossil fuels underlines the need for firm biostratigraphic subdivision. Figure 1. Regional overview of Australia showing the location and extent of the Officer Basin, and adjacent basins, including the positions of the drillcores studied. The Precambrian – life evolves, the environment changes The Precambrian1 spans almost 90 % of Earth’s history but, despite the long duration, we know surprisingly little about early life and the evolutionary history of Precambrian organisms. However, it was during this period that many key evolutionary traits first evolved. Especially important were the 1 The Precambrian is an informal but widely used term that encompasses the time prior to the Cambrian, i.e. before 542 Ma ago. 14 ability for organisms to produce (and later use) oxygen2 that changed the Earth's atmosphere from an anoxic to an oxic state, the evolution of eukaryo- tes, the invention of sexual reproduction and multicellularity. It is unclear how, when and where life first evolved but the earliest evidence comes in the form of biogeochemical fractionation diagnostic of life 3.8 billion years (Ga) ago (Mojzsis et al. 1996). The earliest organisms were probably single- celled prokaryotic organisms (from the Archaea and/or Bacteria domains) that used chemical pathways to obtain energy. Carbonaceous structures re- sembling such
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