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A major new volume on Edicaran palynomorph taxonomy and biostratigraphy has just been published:
Grey, K., 2005. Ediacaran Palynology of Australia. Memoir of the Association of Australasian Palaeontologists 31, 439p.
Abstract Only limited progress has been made towards developing Proterozoic zonal schemes similar to those established in the Phanerozoic. In part, this reflects taxonomic uncertainty, morphological simplicity, slow evolution rates, sporadic distribution patterns and perceptions of low species diversity. However, it also results from a lack of rigorous biostratigraphic analysis. Demands for improved Neoproterozoic correlation and the discovery of well preserved acanthomorphs in drill core have encouraged biostratigraphic studies of Australian Ediacaran successions. More than nine-hundred samples from twenty drill-core and ten field sections in the Centralian Superbasin and Adelaide Rift Complex show that biostratigraphic correlation is feasible, based on large, morphologically complex, acanthomorph acritarchs extracted using improved palynological techniques. Their abundance, complex morphology, wide lithological and geographical distribution and restricted time ranges make acritarchs ideal biostratigraphic tools.
Seventy-one identifiable palynomorph taxa are recorded. Forty-four are specifically identified and twenty-seven either tentatively assigned or placed in open nomenclature. The sixty-four acritarch taxa consist of forty-nine acanthomorphs, twelve sphaeromorphs and four coenobia. Twenty-six acritarchs belong to existing taxa (many substantially emended), and there are seven new combinations. Twenty-six new species and six new genera are described (Archaeotunisphaeridium, Australiastrum, Ceratosphaeridium, Labruscasphaeridium, Pennatosphaeridium and Taedigerasphaera). The remaining palynomorphs are filaments and problematica.
Ediacaran assemblages in the Centralian Superbasin and Adelaide Rift Complex are taxonomically diverse. Range plots produce patterns suitable for zonation and two palynofloras and five Ediacaran assemblage zones have been recognised. An older palynoflora, the Ediacaran Leiosphere-dominated Palynoflora (ELP), has one assemblage zone. It is succeeded by a younger Ediacaran Complex-Acanthomorph-dominated Palynoflora (ECAP) that contains four assemblage zones. The zones, which are demonstrably independent of lithology, can be recognised across the Adelaide Rift Complex and Officer and Amadeus Basins, despite taphonomic and palaeoenvironmental influences. Some taxa resemble species from probably coeval successions in China, Siberia and northern Europe, suggesting that the proposed zonation scheme has good potential for global application.
The Australian Ediacaran shows a marked and rapid increase in abundance, size, morphological complexity and taxonomic diversity that indicates major diversification and significant evolutionary changes. Observed biotic changes are radical and the actual or presumed position of the transition matches a short-lived negative ä13Corg excursion that approximates to the Acraman impact layer, followed by a marked positive excursion that corresponds to the acanthomorph diversification. Evidence for a relationship between the impact event and palynofloral diversification is largely circumstantial and requires further testing. The aftermath of a large bolide impact supplies a plausible explanation for dramatic changes that are otherwise difficult to explain, but further data must be collected to confirm observations presented here.
This volume is available from:
The Business Manager Geological Society of Australia 706 Thakral House 301 George Street Sydney NSW 2000 AUSTRALIA
Tel: (+61 2) 9290 2194 Fax: (+61 2) 9290 2198 E-mail: sue@gsa.org.au
Price: Australia: $141.00 (incl. P & H and GST) Overseas: $150.00 (economy air)
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