Stratigraphy, sedimentology, and geochemistry of the Pandurra Formation

Abstract

Life on Earth during the Mesoproterozoic was challenging with an aggressive low oxygen atmosphere, acidic hydrosphere, intense weathering of the lithosphere, and simple bacteria-plankton biosphere. The research within the following thesis investigates the interaction between the atmosphere, hydrosphere, lithosphere, and biosphere through an assessment of provenance, sedimentology, and characterisation of mineral systems of the Pandurra Formation in southern Australia during the Mesoproterozoic. The Pandurra Formation preserves evidence of the gradual erosion of the Gawler Range Volcanics and subsequent climate variation of the region. This study characterises the mechanisms for sedimentation of the Pandurra Formation from the rapid lateral and vertical variation that resembles a multi-thread anabranching braided distributive fluvial system. This research identifies seven lithological associations that are not consistent with the existing four-member model. This investigation reveals that the Pandurra Formation commenced sedimentation soon after 1562 ± 32 Ma. The zircon geochronology of the Pandurra Formation is similar that of the underlying pre-Mesoproterozoic basement geology, and matches with the observed regional geology of the Archean (2560 to 2500 Ma) and late Palaeoproterozoic to early Mesoproterozoic (1900 to 1450 Ma) Gawler Craton. Sm-Nd isotopic geochemistry reveals that the source age of the Pandurra Formation sediments varied with time from Archean dominated to Palaeoproterozoic back to an Archean signature. This research indicates a connection with the Pandurra Formation to the coeval Belt-Purcell Supergroup in North America, but not to the Rocky Cape Group in Tasmania or the East Antarctic Shield during the Mesoproterozoic. The Pandurra Formation represents a series of elevated terrestrial distributive fluvial systems that supplied sediment to the deep water Pritchard Formation from 1470 to 1454 Ma. Evidence of two fluid flow events at 1211 ± 24 Ma (Vanguard-1) within the Pandurra Formation and at 469 ± 28 Ma (WHD-1) within the overlying Beda Volcanics is described. The spatial and detrital relationship between the Pandurra Formation and Palaeoproterozoic to early Mesoproterozoic IOCG-U enriched basement, indicates the potential to for the sedimentary sequence to host placer (Au and heavy mineral) and remobilised U and/or Cu systems. The Pandurra Formation within Vanguard-1 and numerous other diamond drill cores exhibit kaolinite-dickite and sericite alteration, typical of unconformity U and low temperature epithermal systems. The Beda Volcanics are determined to be prospective for Mississippi Valley-type systems (Pb-Zn-Ba), similar to that in the Adelaide Fold Belt during the waning stages of the ca. 510 to 490 Ma Delamerian Orogeny. The closure age of 1211 ± 24 Ma (Vanguard-1) precludes further hydrothermal activity during the Delamerian Orogeny within the Pandurra Formation.