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Type: Thesis
Title: Geological setting of the Late Proterozoic Wonoka Formation at Pichi Richi Pass, southern Flinders Ranges, South Australia: geochemical, stable isotope and diagenetic analysis
Author: Ayliffe, D.
Issue Date: 1992
School/Discipline: School of Physical Sciences
Abstract: Carbon, oxygen and strontium isotope stratigraphy has increased the resolution of Proterozoic stratigraphic correlation. Isotopic analysis was performed on the late Proterozoic Wonoka Formation canyon and carbonate platform sequences. Highly depleted and homogenised carbon and oxygen isotopes characterise the canyon fill (13C = -8 to -7%o, (18O = - 17 to -15%o PDB ) whilst a major positive excursion was observed in the Wonoka Formation carbonate platform sequence ((13C = -8 to -0.5%o, (18O = -15.0 to -7.0%o PDB). These values correlate closely with other established isotopic trends throughout the Adelaide Geosyncline. However, similar aged late Vendian strata throughout the world show low positive values. Strontium isotopic analysis revealed relatively 87Sr enrichment in the carbonate platform deposits compared to the canyon sequence. This was attributed to the input of 87Sr enriched terrestrially derived strontium. The 87Sr/86Sr ratio of the Wonoka Formation correlates closely with established late Proterozoic seawater trends. Therefore, a primary strontium isotopic composition is implied for the Wonoka Formation. Major and trace element geochemical analysis (Ca, Mg, Sr, Fe, Mn, and Rb) was performed to assess the diagenetic alteration of the late Proterozoic strata. Samples with low Mn/Sr, high Ca/Sr, high strontium, and low rubidium have the highest probability of preserving a primary geochemical signal. Most samples from the Pichi Richi region analysed plotted under the altered Mn/Sr (<2) and Ca/Sr (<2000) values. The high remnant strontium-concentrations of the Wonoka Formation suggest neomorphism from an aragonitic precursor. Micritic carbonate of the Wonoka Formation was probably a primary marine precipitate of aragonite derived from late Proterozoic supersaturated seas. Therefore, the majority of sediment diagenesis probably occurred in the marine phreatic zone, resulting in the observed primary isotopic composition.
Dissertation Note: Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 1992
Where: Adelaide Geosyncline, Flinders Ranges, South Australia
Keywords: Honours; Geology; Adelaidean; Wonoka Formation; platform carbonates; isotopic composition; geochemistry; sedimentary facies
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