Cambrian evolution of the earth’s system: integrated chemostratigraphy and geochronology of Cambrian sequences in the east Warburton Basin, South Australia

Abstract

The early Paleozoic Warburton Basin is considered to be the economic basement to the stacked petroleum producing Cooper-Eromanga system. However, it is one of the least studied subsurface basins in Australia in the context of its depositional, stratigraphic and tectonic histories. This study provides enhanced chronostratigraphic resolution and constraints on surficial and crustal processes, including depositional environment, palaeo-redox and basin restriction via high resolution stable and radiogenic isotope proxies (δ13C, 87Sr/86Sr) and major/trace elemental analysis on Cambrian-aged marine carbonates from two petroleum wells (Gidgealpa 7 and Kalladeina 1) in the East Warburton Basin. U/Pb zircon geochronology of the unconformably underlying Cambrian Mooracoochie Volcanics provided additional, absolute chronological constraints. 87Sr/86Sr isotopes and REE analysis were used to assess the controversial vuggy dolomite found in Gidgealpa wells to determine the origin of dolomitization. δ13C results provide enhanced chronostratigraphic resolution for both wells throughout the middle-late Cambrian (~510 to ~495 Ma) by means of identification of a number of globally recognised Cambrian carbon isotope excursions (CIE’s), (i.e., SPICE, DICE and ROECE). Coupled with sedimentary/gamma logs, this study puts forward evidence for a transgression during the SPICE. 87Sr/86Sr isotope data are extremely locally radiogenic compared to those of expected coeval Cambrian paleo-seawater, suggesting basin restriction: REE analysis suggests oxic conditions. Absolute age constraints from U/Pb zircon geochronology yielded best ages of 509.1 ±2.1 Ma and 510.8 ±3 for Gidgealpa 7 and Kalladeina 1, respectively. Lastly, this study provides evidence for both karstification (marine/meteoric isotope signature) and hydrothermal fluid dolomitization (Eu anomalies) for the origin of the vuggy dolomite. Overall, this study delivers unprecedented constraints on the geochronostratigraphic framework for the East Warburton Basin through the identification of a number of global Cambrian CIE’s and U/Pb geochronology on Cambrian aged sequences, with evidence for basin restriction, oxic conditions and a complex interplay between karstification and hydrothermal fluid dolomitization for origin of vuggy dolomite.