| 1. |
- Grey, Kathleen, et al.
(författare)
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Neoproterozoic subdivision in Australia
- 2005
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Ingår i: Central Australian Basins Symposium.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 2. |
- Grey, Kathleen, et al.
(författare)
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Subdividing the Ediacaran of Australia using biostratigraphy
- 2005
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Ingår i: Central Australian Basins Symposium.
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Konferensbidrag (refereegranskat)abstract
- A new Global Stratotype and Section (GSSP) for the terminal Neoproterozoic, the Ediacaran Period and System, has been ratified by the International Union of Geological Sciences (IUGS), but problems of subdivision and correlation remain. Hydrocarbon and mineral exploration in the Officer, Amadeus, and Georgina basins, and the Adelaide Rift Complex has resulted in the development of palynological (mainly acritarch) correlations using range charts, based on >1000 samples from >30 drillholes sampled about every 10 m. As in the Cryogenian, biostratigraphic correlations, based on palynology and stromatolite biostratigraphy, are feasible, and results are consistent with correlations based on carbon isotope curves established using splits of palynology samples.So far, zonation is only possible for the lower and middle Ediacaran in Australia. Upper Ediacaran lithologies are generally unsuitable for palynomorph preservation and assemblages appear to be highly impoverished. However, a distinctive assemblage of large acanthomorph acritarchs, with highly complex morphologies and short stratigraphic ranges, characterises the middle Ediacaran. They are ideal candidates for biostratigraphy and this interval can be correlated with a high degree of confidence. Assemblages from Baltica and the East European Platform suggest that palynological zonation of the upper Ediacaran may be possible, despite species reduction and a return to simple morphologies. Moreover, the upper Ediacaran contains the Ediacara fauna, which may also be a suitable tool for correlation.Stromatolites indicate Australia-wide correlation at certain levels of the Ediacaran. Incipient columns of Elleria minuta, characteristic of the Amadeus Basin (Marinoan-equivalent) cap dolomite, were identified in a 50 cm-thick dolomite horizon above a diamictite, in Empress-1/1A in Western Australia. Tungussia julia is widespread and appears to be facies independent. It occurs in shallow-water carbonates of the Julie Formation (Amadeus Basin), Wonoka Formation (Adelaide Rift Complex), Elkera Formation (Georgina Basin), and Wilari Dolomite Member of the Tanana Formation (eastern Officer Basin), and is present in the periglacial Egan Formation in the Kimberley area. Relative stratigraphy indicates that the Egan Formation is considerably younger than the Elatina Formation (Marinoan glaciation). The Egan glaciation took place at about 560 Ma, only a short time before the appearance of the first bilaterian trace fossils.Palynomorph assemblages are sparse during and between the Sturtian and Marinoan glaciations (~700–600 Ma) and samples immediately above the Marinoan glaciation are barren. Post-glacial benthic mats and leiospheres quickly re-established and flourished, as sea level and temperatures rose, but there is no obvious post-glacial species diversification, and no evidence of invasion by extremophiles from hot-spring refugia as envisaged in Snowball Earth predictions. Only a handful of species survived, but pre-glacial species appear to be identical to post-glacial species. Specimen numbers increased rapidly as sea-level rose, but so far, no new taxa have been identified below the Acraman impact ejecta layer.Above the Acraman impact layer, during a second sea-level rise, there is a striking change in the palynoflora, when >50 species of large acanthomorph acritarchs, belonging to several new genera, first appear and diversify rapidly. They differ significantly from older taxa and in some aspects resemble dinocysts. At least four zones have been recognised, based mainly on assemblages from continuous core in the eastern Officer Basin (Munta-1, Observatory Hill-1, Lake Maurice West-1, and Birksgate-1), the Adelaide Rift Complex succession (SCYW-1a, WWD-1 and MJ-1) and the Amadeus Basin (Wallara-1 and Rodinga-4). More detailed studies are in progress on distributions in Lake Maurice West-1, Observatory Hill-1, Murnaroo-1, and Giles-1. These drillholes are of particular significance because the precise position of the ejecta layer is known in each.Although the acanthomorph assemblage was recognised previously in Murnaroo-1, systematic sampling was not carried out and the position of the ejecta layer was not known. More refined sampling and the discovery of the ejecta layer at 279.55 m has now confirmed observations from other drillholes that the earliest appearance of the acanthomorphs is above the ejecta layer and that diversification was rapid, with 10 species already present, less than 50 m above the ejecta layer. Studies continue in an attempt to locate the earliest appearance of acanthomorphs. Preliminary examination of samples from Giles-1, where the ejecta layer was found at 554.90 m, confirms the acritarch distribution pattern. Stable isotope studies are also providing significant data about the effect of the Acraman impact on the biosphere.Several key acanthomorph species are present elsewhere in the world, including Svalbard, Norway, Siberia, and China, raising the possibility of global correlation. In particular, the Australian assemblage has several taxa in common with a succession in an area in eastern Siberia that contains one of the giant Neoproterozoic gas fields. Further work is required to define the ranges of key species outside Australia, so the scheme can be extended globally.At present, contradictions arise when correlations are attempted with the Doushantuo Formation in China. In part, this reflects the lack of methodical stratigraphic sampling in the Chinese succession and the disparity in thickness between the Chinese succession (<200 m) and the Australian succession (>2000 m). There are also discrepancies in the acritarch biostratigraphy and carbon isotope curves that raise issues about whether the Nantuo Tillite should be correlated with the type ‘Marinoan’ glaciation, the Elatina Formation, and these discrepancies have implications about how many glacial episodes happened in the Neoproterozoic. Recent dating on probable equivalents of the Elatina Formation in King Island and Tasmania suggest an age of 580 Ma. This is similar to the age of the Gaskiers and Squantum Tillites in western Canada, but considerably younger than recently obtained ages of 635 Ma on successions in southern Africa and the Nantuo Tillite in China.Prospects for subdividing and correlating the Ediacaran using biostratigraphy are excellent, provided taxonomic ranges are properly documented. Biostratigraphic subdivisions can be integrated with other means of correlation to provide a rigorous means of global correlation.
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| 3. |
- Grey, Kathleen, et al.
(författare)
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Taphonomy of Ediacaran acritarchs from Australia: significance for taxonomy and biostratigraphy
- 2009
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Ingår i: Palaios. - : Society for Sedimentary Geology. - 0883-1351 .- 1938-5323. ; 24:3-4, s. 239-256
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Tidskriftsartikel (refereegranskat)abstract
- A diverse assemblage of Australian Ediacaran (late Neoproterozoic) acritarchs from the Centralian Superbasin and Adelaide Rift Complex demonstrates a range of taphonomic degradation. Recognition of taphonomic variants is critical for taxonomic studies and biostratigraphic interpretation. Taphonomic features observed include compression features, folding and tearing of vesicle walls, pitting, perforation, abrasion, exfoliation, shrinking, twisting, splitting, curling, shredding, pyritization, particle entrapment, and thermal maturation effects. The physical and chemical structure of the vesicle wall is instrumental in determining the degree of taphonomic damage. Consistent associations allow Identification of degradation series that incorporate previously described individual species and provide a framework for taxonomic revision. Taphonomic associations may also characterize taphofacies, providing an additional tool for basin analysis.
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| 4. |
- Hill, Andrew C., et al.
(författare)
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New records of Ediacaran Acraman ejecta in drillholes from the Stuart Shelf and Officer Basin, South Australia
- 2007
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Ingår i: Meteoritics and Planetary Science. - 1086-9379 .- 1945-5100. ; 42:11, s. 1883-1891
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Moczydlowska, Malgorzata, et al.
(författare)
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Ultrastructure of cell walls in ancient microfossils as a proxy to their biological affinities
- 2009
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 173:1-4, s. 27-38
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Forskningsöversikt (refereegranskat)abstract
- Bacteria and protoctists dominated the biosphere in the Archean and Proterozoic, their affinities being deduced by studies of their comparative morphology, palaeoecology, biogeochemistry, and wall ultrastructure. However, exact phylogenetic relationships are uncertain for most such microfossils. Because of the limitations imposed by the simple morphology and small dimensions of such microorganisms and their little known biochemistry, new techniques in microscopy, tomography and spectroscopy are applied to examine individual microfossils at the highest attainable spatial resolution. TEM/SEM studies of the wall ultrastructure of sphaero- and acanthomorphic acritarchs have revealed complex, single to multilayered walls, having a unique texture in sub-layers and an occasionally preserved trilaminar sheath structure (TLS) of the external layer. A variety of optical characteristics, the electron density and texture of fabrics of discrete layers, and the properties of biopolymers may indicate the polyphyletic affiliations of such microfossils and/or the preservation of various stages (vegetative, resting) in their life cycle. Primarily, wall ultrastructure allows discrimination between fossilized prokaryotic and eukaryotic cells. Composite wall ultrastructure provides evidence that some Proterozoic and Cambrian leiosphaerids are of algal affinities (but not, per se, that they are referable to "Leiosphaeridia"). Certain Cambrian specimens represent chlorophyceaens, having the multilayered composite wall with TLS structure known from vegetative and resting cells in modern genera of the Chlorococcales and Volvocales. The wall ultrastructure of the studied Cambrian and Proterozoic acanthomorphs resembles the resting cysts of green microalgae, but there is no evidence to suggest a close relationship of these taxa, to dinoflagellates. It is apparent that although there is no single and direct method to recognize the precise phylogenetic relations of such microfossils, ultrastructural studies of their preserved cell walls and encompassing sheaths, combined with biochemical analyses and other advanced methods, may further elucidate their affinities to the modern biota.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Willman, Sebastian
(författare)
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A PRECAMBRIAN EXPLOSION?
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The well-known Cambrian explosion was an evolutionary event that lacks counterparts in Earth history. The appearance of shelly organisms easily preserved as fossils illustrates an exceptional record of diversifying organisms. It is established that this was a true biological diversification but was it the first one? The Cambrian was preceded by the Neoproterozoic, a period that was characterised by severe environmental turbulence during its terminal interval (Ediacaran). At least two global glaciations between ca. 700-580 Ma might have acted as evolutionary bottlenecks that led to a rapid diversification of several lineages of single-celled and, eventually, multicellular organisms. The appearance of more than 50 ornamented acritarchs (Grey et al., 2003) in the Ediacaran of present day southern Australia suggests a possible Precambrian evolutionary explosion. Acritarchs, being primary producers, may have had a profound effect on the evolution of metazoans resulting, among other factors, in the Cambrian explosion. The apparent diversification event requires studies of more material but will hopefully result in either recognition of a Precambrian explosion hypothesis or simply a normal, gradual development of phytoplankton.The diversification of acritarchs provides an excellent potential for these organisms to be used in biostratigraphy. The Ediacaran System’s lower boundary is defined at the base of glacial deposits from the last major glaciation, the Marinoan glaciation, and the upper boundary at the base of the Cambrian System. The Ediacaran System is not very well known and in terms of fossil studies it is just in its infancy. Palynomorph assemblages containing mainly eukaryotic acritarchs and prokaryotic bacteria were recovered from numerous drillholes located in southern Australia. Preliminary studies of a large number of acritarch samples from more than 30 drillcores (Grey, 2005) have resulted in a subdivision of the middle Ediacaran into biozones based on the first appearance of index species and characteristic assemblages. Additional studies of drillcores from the Officer Basin in Australia will aid in the correlation between different basins in Australia and hopefully also in global correlation. The studies of the Murnaroo 1 succession indicate a consistency with the previously examined boreholes and allow more accurate recognition of the acritarch biozones.Grey, K., Walter, M.R. & Calver C.R., 2003. Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology, v. 31.Grey, K., 2005, in press. Ediacaran Palynology of Australia. Australasian Association of Palaeontologists, Memoirs, v. 31.
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| 10. |
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| 11. |
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| 12. |
- Willman, Sebastian, et al.
(författare)
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Acritarchs in the Ediacaran seas
- 2005
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Ingår i: The Palaeontological Association. ; , s. 64-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The terminal Neoproterozoic radiation of planktonic photosynthetic microbiota (acritarchs) is one of the most significant evolutionary events of the time, including diversification of prokaryotic cyanobacteria and eukaryotic green and brown algae, the appearance of thecoamoebaens and subsequently metazoans (the Ediacara fauna). The Ediacaran radiation of phytoplankton is recognizable by the first appearance of more than fifty new species of large ornamented acritarchs in a short interval of time at ca. 570 Ma. This radiation event occurred after the Snowball Earth conditions returned to a kind of "normal" environmental stasis, and it may be interpreted as a recovery diversification of phytoplankton after a major biotic extinction caused by the global glaciation.The appearance of numerous, morphologically innovative and large acritarch taxa may also be connected with the Acraman impact event in South Australia, suggested recently by Grey et al. (2003), as a biotic recovery after the catastrophic environmental disturbance caused by the giant bolide. The latter hypothesis has to be tested, however, because a few individual taxa of ornamented acritarchs may have actually appeared below the ejecta layer, which is difficult to recognize with certainty in some borehole successions.The Ediacaran acritarch records are from Australia (the Officer and Amadeus Basins), China and Siberia, showing a worldwide distribution in a relatively short interval of time (ca. 20 Ma; Grey, 2004, in press). The greatest taxonomic diversity is known from Australia (ibidem), and the present study is focused on the investigation of Ediacaran microbiota in greater detail and from different stratigraphic levels, their palaeobiology and affinities, mode of life and reproduction cycle. The new assemblage of organic-walled microfossils from the Murnaroo 1 borehole comprises filamentous cyanobacteria, and ornamented and spheroidal acritarchs.The Ediacaran successions in Australia have been well documented in terms of lithostratigraphy, depositional settings and structural geology. The sedimentation proceeded in two different depositional regimes, recognized today in a series of sub-basins. One of them is the Officer Basin, comprised of complex intracratonic, east-west trending troughs and sub-basins extending from Western Australia to South Australia. The studied Murnaroo 1 borehole is also located there. The sediments accumulated in tidal, sub- and intertidal shelf conditions, and the predominantly mudstone lithology from which the samples were collected, is ideal for palynological processing and preservation of microfossils. The lack of macrofossils in the successions rendered efforts and advances in acritarch biostratigraphy since the 1980's, which helped to reveal a complex history of the Officer Basin. The discovery of two distinct palynofloras, an older leiosphere-dominated flora (ELP) and a younger acanthomorph-dominated flora (ECAP), is suggested to be largely environmentally independent (Grey, 2004, in press) in terms of the observed lithology and sedimentological sequences. However, the possible coupling between the Marinoan glaciation, the Acraman impact and the radical change in the palynofloras was inferred (ibidem) and this will be examined with the new data available from the Murnaroo 1 borehole. Previously, the Murnaroo succession was only studied preliminarily.In my communication, I will discuss the stratigraphic sequence of appearances of various species and their relationship to the environmental conditions, the Acraman impact event and the changes associated with the global glaciations.GREY, K., WALTER, M.R. and CALVER, C.R. (2003) Neoproterozoic biotic diversification: "Snowball Earth" or aftermath of the Acraman impact? Geology 31, p. 459-462.GREY, K., (2004, in press) Ediacarian Palynology of Australia. Australasian Association of Palaeontologists, Memoirs.
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| 13. |
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| 14. |
- Willman, Sebastian
(författare)
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Can acritarchs be used for Ediacaran suddivision?
- 2008
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Ingår i: Geology and hydrocarbon potential of the Neoproterozoic-Cambrian Basins in India, Pakistan and the Middle East. ; , s. 19-21
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Konferensbidrag (refereegranskat)abstract
- can acritarchs be used for ediacaran subdivison? Willman, Sebastian Uppsala University, Department of Earth Sciences, Palaeobiology, Villavägen 16, SE-752 36 Uppsala, Sweden. Email: Sebastian.Willman@geo.uu.se The fossil record of the three billion years before the Cambrian is patchy, but shows that early organisms had adapted to a variety of environments and that many major evolutionary innovations such as multicellularity, sexual reproduction and tissue formation occurred early in life history. The fossil record of the earliest prokaryotes is debated (e.g., Schopf, 1993; Brasier et al., 2002) but that of eukaryotic protists is better understood, although by no means well established. Protists and problematic biotas of limited diversity, including e.g., Grypania, are present between 2.5 and 1.5 Ga. Younger rock successions between 1.5 Ga and 750 Ma in age include more morphologically complex fossils such as Chuaria and Tawuia as well as the possible red algae Bangiomorpha (Knoll et al., 2006 gives an up to date summary of Proterozoic eukaryotes). However, it is not until the Ediacaran that organisms of undoubtedly metazoan affinities first appear (e.g., Narbonne, 2005). The Ediacaran biota remains largely problematic and even though the fossils are spread globally their distribution is uneven. Conversely, organic-walled microfossils referred to as acritarchs are commonly recorded throughout Meso- and Neoproterozoic rock successions worldwide. The Neoproterozoic was a time of major environmental change. At least two, possibly three, and even four global glaciations have been suggested to cover the entire Earth with thick ice during the Cryogenian Period (e.g., Hoffman et al., 1998). Following the last glaciation, the Marinoan glaciation, greenhouse conditions prevailed during the Ediacaran and caused major shifts in ocean geochemistry, oceanic stratification and oxygenation, and evolution of the marine biosphere (Kirschvink, 1992; Canfield, 1998; Shields et al., 1998; Grey, 2005; Fike et al., 2006; Canfield et al., 2007). It was during the Ediacaran that the first major diversification of organic-walled acritarchs occurred. This diversification is preserved in rock successions worldwide, including Siberia, China, Baltica, India and, especially, in the Centralian Superbasin in Australia. Grey et al. (2003) noted that the first appearance of acanthomorphic (ornamented) acritarchs in samples from drillcores in the Officer and Amadeus Basins and the Adelaide Rift Complex, occurred stratigraphically above a bolide ejecta layer, the result of a large impact some 580 Ma years ago (the Acraman impact; Walter et al., 2000). A problem in Neoproterozoic subdivision has been the lack of biostratigraphic control (Knoll & Walter, 1992), and although Neoproterozoic biostratigraphy is increasingly well-understood it is still a highly debated theme. As a result, anything and everything that can aid in the correlation of Ediacaran successions is especially sought after. The tools for correlation of the Neoproterozoic currently at hand include chemostratigraphy, sedimentology, event stratigraphy (impacts, glacial episodes, volcanic eruptions and the alike), magnetostratigraphy, and the subject of this presentation: Ediacaran biostratigraphy. The Officer Basin in South Australia is an intracratonic basin that extends some 1400 km in an east-west trend across Western and South Australia. Stratigraphic correlation of the Officer Basin has been based mainly on seismic, magnetic, and gravity studies but was recently reviewed by Grey (2005). The succession studied here (and in Grey, 2005) is the largely siliciclastic lower Ungoolya Group which, in ascending stratigraphic order, consists of the Dey Dey Mudstone, the Karlaya Limestone, and the Tanana Formation. The Dey Dey Mudstone is divided into two units separated by a bed of dolomitic intraclasts; the lower unit is mainly red-brown and occasionally green-grey silty mudstone that was deposited in a fluvial environment and the upper unit is a laminated dolomitic or calcareous siltstone and mudstone deposited in slightly deeper, prodelta and shelf environments (Zang, 1995; Morton, 1997). The Karlaya Limestone consists mainly of thin-bedded micritic limestone with dark grey silty mudstone layers and some limestone intraclasts, deposited on a subtidal shelf, probably below fair-weather wave base (Zang, 1995). The Tanana Formation overlies the Karlaya Limestone and consists of micritic limestone with silty mudstone interbeds deposited in a prodelta and distal delta front to shelf settings (Morton, 1997). Microfossils were collected from unevenly sampled intervals in the Giles 1, Murnaroo 1, Lake Maurice West 1, WWD 1, Observatory Hill 1, and Munta 1 drillcores. Samples were selected from lithologies that are suitable for palynological preservation (i.e., unoxidized mudstones, shales, and carbonaceous rocks) and collected from both sides of the Acraman impact ejecta layer. The microfossils are permanently fixed in strew mounts and were observed under transmitted light, and documented using a digital camera. The results of micropalaeontological studies provide further evidence for the acritarch diversification that was so typical for parts of the Ediacaran. Many of the acritarch taxa are stratigraphically constrained and the patterns observed in various drillholes match the patterns first reported by Grey (2005). The new palynological record further supports and enhances the subdivision and stratigraphic correlation of the Ediacaran System in Australia and potentially on a more interregional scale. Acritarchs are well-preserved and diverse, change over short stratigraphic intervals, and allow the recognition of the previously established zones by use of certain acanthomorphic species. The presence of common species and taxonomic similarities between entire assemblages from Australia, Siberia, Baltica, South China and India provide a means for global correlation of the Ediacaran System using palynology. Portions of the Ediacaran System can be confidently proved to be coeval by the occurrence of discrete species distributed across various palaeocontinents and ranging stratigraphically no longer than a few million years. This suggests that they can be used for biostratigraphic analysis and correlation because other fossils are too scarce, too geographically restricted, or too difficult to interpret. Keywords: Ediacaran, Neoproterozoic, Officer Basin, Australia, acritarchs, biostratigraphy References Brasier, M.D., Green, O.R., Jephcoat, A.P., Kleppe, A.K., Van Kranendonk, M.J., Lindsay, J.F., Steele, A., Grassineau, N.V., 2005. Questioning the evidence for Earth's oldest fossils. Nature 416, 76-81. Canfield, D.E., 1998. A new model for Proterozoic ocean chemistry. Nature 396, 450-453. Canfield, D.E., Poulton, S.W., Narbonne, G.M., 2007. Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Science 315, 92-95. Fike, D.A., Grotzinger, J.P., Pratt, L.M., Summons, R.E., 2006. Oxidation of the Ediacaran Ocean. Nature 444, 744-747. Grey, K., 2005. Ediacaran Palynology of Australia. Australasian Association of Palaeontologists Memoir 31, 1-439. Grey, K., Walter, M.R., Calver C.R., 2003. Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology 31, 459-462. Hoffman, P.F., Kaufman, A.J., Halverson, G.P., Schrag, D.P., 1998. A Neoproterozoic Snowball Earth. Science 281, 1342-1346. Kirschvink, J.L., 1992. Late Proterozoic low-latitude global-glaciation: the Snowball Earth. In: Achopf, J.W., Klein, C. (Eds.), The Proterozoic biosphere. Cambridge University Press, 51-52. Knoll, A.H., Javaux, E.J., Hewitt, D., Cohen, P., 2006. Eukaryotic organisms in Proterozoic oceans. Philosophical Transactions of the Royal Society B 361, 1023-1038. Morton, J.G.G., 1997. Chapter 6: Lithostratigraphy and environments of deposition. In: Morton, J.G.G., Drexel, J.F. (Eds.), Petroleum Geology of South Australia, Vol. 3: Officer Basin. South Australia, Department of Mines and Energy Resources Report Book 19, 47-86. Narbonne, G.M., 2005. The Ediacara biota: Neoproterozoic origin of animals and their ecosystems. Annual Review of Earth and Planetary Sciences 33, 421-442. Schopf, J.W., 1993. Microfossils of the Early Archean Apex chert: new evidence of the antiquity of life. Science 260, 640-646. Shields, G.A., Stille, P., Brasier, M.D., Atudorei, V., 1998. Ocean stratification and oxygenation of the Late Precambrian environment: a post-glacial geochemical record from a Neoproterozoic section in W. Mongolia. Terra Nova 9, 218-222. Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P., Hill, A.C., 2000. Dating the 840–544 Ma Neoproterozoic interval by isotopes of strontium, carbon, and sulfur in seawater, and some interpretative models. Precambrian Research 100, 371-433. Willman, S., Moczydłowska, M., Grey, K., 2006. Neoproterozoic (Ediacaran) diversification of acritarchs – A new record from the Murnaroo 1 drillcore, eastern Officer Basin, Australia. Review of Palaeobotany and Palynology 139, 17-39. Zang, W-L., 1995b. Neoproterozoic depositional sequences and tectonics, eastern Officer Basin, South Australia. South Australia. Department of Mines and Energy. Report Book, 1-21.
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| 15. |
- Willman, Sebastian, et al.
(författare)
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Ediacaran acritarch biota from the Giles 1 drillhole, Officer Basin, Australia, and its potential for biostratigraphic correlation
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 162:3-4, s. 498-530
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Forskningsöversikt (refereegranskat)abstract
- The remarkable diversification of single-celled photosynthesising biota of algal and other as yet unknown affinities (acritarchs), followed by the diversification of metazoans, occurred during the Ediacaran Period, which is marked by extreme climatic and environmental changes. Here we describe a taxonomically diverse acritarch association from the Ediacaran part of the Giles 1 drillcore in the Officer Basin, South Australia, which documents further the Ediacaran phytoplankton radiation. The studied palynoflora comprises 21 known acritarch species belonging to 15 genera. One new monospecific genus is described (Calyxia xandaros sp. nov.) as well as one new species of Tanarium (Tanarium anozos sp. nov.). We also propose the genus Knollisphaeridium to replace the preoccupied genus Echinosphaeridium. Three stratigraphically successive assemblages that match previously observed patterns of acritarch replacement are distinguished. The present record is from slightly older strata than in previous records, thus extending the ranges of certain acanthomorphic species. The lower boundaries of three stratigraphically higher assemblage zones among the four formerly established zones, are identified by the occurrence of the index species Tanarium conoideum, Tanarium irregulare and Apodastoides verobturatus, respectively. The substantial morphological disparity of acritarchs in the Giles 1 succession suggests that they may represent a great diversity of microorganisms, not only as biological species but also representing perhaps vegetative and encysted stages in their life cycle. The reconstructed palaeogeographic distribution of several species between Australia, Siberia, Baltica (the East European Platform), and to South China, shows that acritarchs are suitable for both intra- and inter-regional correlation.
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| 18. |
- Willman, Sebastian, Docent
(författare)
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Morphology and wall ultrastructure of leiosphaeric and acanthomorphic acritarchs from the Ediacaran of Australia
- 2009
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 7:1, s. 8-20
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Tidskriftsartikel (refereegranskat)abstract
- Acritarchs are a group of organic-walled microfossils with unknown biological affinities. The wall ultrastructure of the unornamented, smooth Leiosphaeridia sp. and the acanthomorphic Gyalosphaeridium pulchrum from the Ediacaran Dey Dey Mudstone in the Officer Basin, South Australia, was studied by use of transmission and scanning electron microscopy, and transmitted light microscopy. The study of the ultrastructure reveals a complexity in the cell wall not seen in prokaryotes. Wall ultrastructures range from single-layered to three- or four-layered and from homogeneous to porous. Acritarchs with different wall ultrastructures may be different organisms, but may also reflect different stages in a life cycle. In this paper I review previous ultrastructure studies and discuss possible algal and metazoan affinities for the specimens studied herein.
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| 22. |
- Willman, Sebastian
(författare)
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SUBDIVIDING THE EDIACARAN SYSTEM IN AUSTRALIA USING ACRITARCHS
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The terminal Neoproterozoic was a period of time in Earth history that was characterised by severe environmental turbulence. At least two major, global glaciations between ca. 700-580 Ma might have acted as evolutionary bottlenecks that led to a rapid diversification of several lineages of single celled and, eventually, multicellular organisms. A large bolide impact in present day southern Australia at around 580 Ma could also have affected the evolution and diversification of microphytoplankton, at least on a local scale (Grey et al. 2003). The appearance of more than 50 ornamented acritarchs above the impact ejecta layer provides an excellent potential for these organisms to be used in biostratigraphy.The Ediacaran System is defined by its lower boundary occurring between the glacial deposits from the last major glaciation, the Marinoan glaciation, and the overlying cap carbonate, and by the base of the Cambrian System. This system is not very well known and in terms of fossil studies it is just in its infancy. Palynomorph assemblages containing organic walled microfossils, mainly acritarchs and prokaryotic organisms, are recovered from numerous drillholes located in southern Australia. Preliminary studies of a large number of acritarch samples from more than 30 drillcores (Grey 2005) have resulted in a subdivision of the middle Ediacaran into biozones based on the first appearance of index species and characteristic assemblages. Additional studies of drillcores from the Officer Basin in Australia will aid in the correlation between different basins in Australia and hopefully also global correlation. The studies of the Murnaroo 1 succession indicate a consistency with the previously examined boreholes and allow more accurate recognition of the acritarch biozones.Grey, K., Walter, M.R. & Calver C.R., 2003: Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology, v. 31.Grey, K., 2005, in press: Ediacaran Palynology of Australia. Australasian Association of Palaeontologists, Memoirs, v. 31.
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| 23. |
- Willman, Sebastian, et al.
(författare)
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Taphonomic analysis of Ediacaran acritarchs and its importance for taxonomy,biostratigraphy and global correlation
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study we analysed the taphonomic degradation history of a diverse assemblage of Ediacaran(late Neoproterozoic) acritarchs from the Centralian Superbasin and Adelaide Rift Complex inAustralia. Taphonomic features observed include compression features, folding and tearing ofvesicle walls, pitting, perforation, abrasion, exfoliation, shrinking, twisting, splitting, curling,shredding, pyritization, particle entrapment, and thermal maturation effects. The physical andchemical structure of the vesicle wall determines the degree of taphonomic damage. Consistentassociations allowed identification of degradation series which incorporate previously describedindividual species and provide a framework for taxonomic revision. Recognition of taphonomicvariants is an important first step in systematic studies, and tracking degradational pathways forparticular species resulted in more precise taxonomic identification. Other biostratigraphicallyuseful fossils are uncommon in the Neoproterozoic which means that considerable reliance willbe placed on acritarch biostratigraphy for future global correlations. It is vital, therefore, that thesignificance of taphonomic degradation, for both taxonomy and palaeoenvironmental analysis, isgiven adequate recognition. Identification of taphonomic variants is critical for taxonomic studiesand must be considered before making biostratigraphic subdivision of the Ediacaran System.
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| 24. |
- Willman, Sebastian
(författare)
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Testing the role of spines as predatory defense
- 2007
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Ingår i: Journal of Shellfish Research. - 0730-8000 .- 1943-6319. ; 26:1, s. 261-266
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Tidskriftsartikel (refereegranskat)abstract
- Spines are frequently considered to be an important physical defense against predators. This experiment shows that spines do not always function successfully as physical protection. Using natural predators and prey (the drilling muricid gastropod Nucella lamellosa (Gmelin 1791) and the mussel Mytilus trossulus (Gould 1850)) this experiment used artificial spines in different configurations and densities to try to assess the role of spines as predatory defense. The presence of spines did not inhibit the predator from choosing ornamented prey. Greater spine density did not improve the probability of surviving a predator encounter. Although mean handling time increased to some extent with higher spine density, the outcome of the encounter was the same. Presence or density of spines did not deter predators from attacking prey, and experimental prey with greater spine-density experienced greater mortality than did specimens with fewer spines. Drillhole dimensions differed slightly between the treatments, probably as a consequence of difficulties for the gastropod to maneuver its accessory boring organ (ABO) in between the spines.
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| 25. |
- Willman, Sebastian, Docent
(författare)
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The Ediacaran Diversification of Organic-walled Microbiota : Ocean Life 600 Million Years Ago
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 27. |
- Willman, Sebastian, et al.
(författare)
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Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia
- 2007
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 40:2, s. 111-123
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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