Mid-Neoproterozoic biostratigraphy and isotope stratigraphy in Australia

Palynomorph and stromatolite assemblages from mid-Neoproterozoic strata of Australia appear highly significant when collated with results obtained from isotope stratigraphy, and allow correlation across the Centralian Superbasin and Adelaide Rift Complex. The majority of palynomorphs from the lower mid-Neoproterozoic (similar to 830 Ma) have limited biostratigraphic value, although a few apparently have restricted ranges. Carbonates at this stratigraphic level contain the distinctive stromatolite Acaciella australica and other taxa of the Acaciella australica Stromatolite Assemblage. These carbonates have delta(13)C(carb) values of between -4 and 0 parts per thousand, and associated anhydrite has Sr-87/Sr-86 ratios of 0.7069. These depleted delta(13)C(carb) values are immediately preceded by values of 6.1%0 in the western Officer and Amadeus Basins of the Centralian Superbasin. Similar C and Sr isotopic features are seen in the similarly aged upper Shaler Supergroup of Canada. Upper mid-Neoproterozoic (similar to 760Ma) carbonates contain the distinctive stromatolite Baicalia burra and other stromatolites of the Baicalia burra Stromatolite Assemblage. Siliciclastic horizons in the same interval contain the acritarch Cerebrosphaera buickii, and have delta(13)C(carb) values of between 0 and 8 parts per thousand. The highest mid-Neoproterozoic delta(13)C(carb), values of between 6.7 and 8.1 parts per thousand occur within the stratigraphic range of C. buickii in Australia. In the western Officer Basin and Adelaide Rift Complex the mid-Neoproterozoic delta(13)C(carb) peaks are preceded by values of ca. 0 parts per thousand. The apparently restricted range of C. buickii in Australia suggests the need for reinterpretation of the stratigraphic position of its occurrence in the Svanbergfjellet Formation, Akademikerbreen Group, Spitsbergen, which was previously considered a post-Sturtian-glacial deposit. Crown copyright (C) 2000 Published by Elsevier Science B.V. All rights reserved.