Geochronology, Provenance, and Tectonic Evolution of the Adelaide Superbasin, South Australia

The Neoproterozoic (1000–538 Ma) was a period of some of the most significant changes to Earth’s systems throughout its c. 4.5-billion-year history. The tectonic system drove the final amalgamation of Rodinia, subsequent breakup coinciding with the emplacement of numerous large igneous provinces, and the initial stages of Gondwana amalgamation during the late Ediacaran. Current evidence suggests two long lived global glacial events occurred, the Sturtian and Marinoan glaciations, with both thought to be Snowball Earth events. These significant changes driven by Earth’s systems appear to have culminated in a nutrient rich ocean, a progressive rise in atmospheric oxygen concentration, the proliferation of eukaryotic and metazoan life, and the evolution of the earliest confirmed animalia, the Ediacaran fauna.
\nThe Neoproterozoic–Cambrian rocks of the redefined Adelaide Superbasin (formerly Adelaide Geosyncline) hold one of the most complete records of this pivotal time in Earth’s history. These records include key sequences of the Cryogenian global glaciations, the Ediacaran Acraman bolide ejecta layer, the eponymous Ediacaran fauna, and the global boundary stratotype section and point (GSSP) for the base of the Ediacaran.
\nDespite the important record the Adelaide Superbasin holds, our knowledge of the chronology and tectonic evolution of it is still a hindrance to the calibration of other investigative techniques like chemostratigraphy, and for the development of global correlation frameworks for these Earth system events and stratigraphic sequences. While a significant corpus of research has been done to address these same issues around the globe, particularly in Canada, China, Ethiopia, Namibia, Scotland, and Svalbard, geochronology of Neoproterozoic sequences remains a significant challenge due to the fragmented, eroded, and commonly deformed stratigraphic record of the Neoproterozoic. The primary purpose of this research is to address the knowledge gap in the detrital zircon record of the Adelaide Superbasin to refine the chronostratigraphic framework, and to revise the tectonic and palaeogeographic model for the Adelaide Superbasin within the Neoproterozoic.
\nThis thesis presents over 6,500 new detrital zircon data from a significantly greater spatial and temporal diversity of samples from the Neoproterozoic of the Adelaide Superbasin—this is approximately half of the now available detrital zircon data for the basin. The research presented here suggests that deposition in the Adelaide Superbasin began between c. 890 Ma and 830 Ma, in half-graben depocentres resultant from far-field extensional forces. The rift system propagated along existing crustal weaknesses in an overall southerly direction, with major extensional pulses c. 830 Ma, c. 790 Ma (north), and c. 750–730 Ma (south) reflected by abrupt changes in zircon provenance. The northern region of the Adelaide Superbasin became an aulacogen with the opening of the proto-Pacific likely developing in the southern regions of the basin, heading northeast around the Curnamona Province. Detrital zircon spectra show a return to predominantly local sediment derivation during deposition of the Yudnamutana Subgroup, representative of the Sturtian glaciation. This is attributed to both glacial scouring of the surrounding region and disruption in sediment supply from distal sources due to the widespread nature of the glaciation. Beyond this time, derivation from distal sources became increasingly prevalent as the basin continued to develop through sag phases, with overall sedimentation becoming gradually shallower through the Neoproterozoic as the basin filled. This research has also led to a suggestion that an unrecognised Stenian–Tonian zircon source lay to the north/northeast of the basin. Finally, the rocks characterised by thick glaciogenic diamictite in the Yudnamutana Subgroup are all redefined as the Sturt Formation, resolving years of conjecture.

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