Sedimentary rocks along the southern margin of Australia host an important record of the 18 break-up history of east Gondwana, as well as fragments of a deeper geological history, which collectively help inform the geological evolution of a vast and largely underexplored 20 region. New drilling through Cenozoic cover has allowed examination of the Cretaceous riftrelated Madura Shelf sequence (Bight Basin), and identification of two new stratigraphic units beneath the shelf; the possibly Proterozoic Shanes Dam Conglomerate and the 1 interpreted Palaeozoic southern Officer Basin unit, the Decoration Sandstone. Recognition of these new units indicates an earlier basinal history than previously known. Lithostratigraphy of the new drillcore has been integrated with that published from onshore and offshore cores to present isopach maps of sedimentary cover on the Madura Shelf. New palynological data demonstrate progression from more localized freshwater-brackish fluviolacustrine clastics in the early Cretaceous (Foraminisporis wonthaggiensis-Valanginian to Barremian) to widespread topography-blanketing, fully marine, glauconitic mudrocks in the mid Cretaceous (Endoceratium ludbrookiae-Albian). Geochronology and Hf-isotope geochemistry show detrital zircon populations from the Madura Shelf are comparable to those from the southern Officer Basin, as well as Cenozoic shoreline and palaeovalley sediments in the region. The detrital zircon population from the Shanes Dam Conglomerate is defined by a unimodal ~1400 Ma peak, which correlates with directly underlying crystalline basement of the Madura Province. Peak ages of ~1150 Ma and ~1650 Ma dominate the age spectra of all other samples, indicating a stable sediment reservoir through much of the Phanerozoic, with sediments largely sourced from the Albany-Fraser and Musgrave Orogens (directly and via multiple recycling events). The Madura Shelf data differ from published data for the Upper Cretaceous Ceduna Delta to the east, indicating significant differences in sediment provenance and routing between the Ceduna Sub-basin and central Bight Basin.

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During 2013 and 2014, eight new boreholes were drilled to basement across the Nullarbor Plain in Western Australia under a Geological Survey of Western Australia Exploration Incentive Scheme (Spaggiari and Smithies, 2015). These boreholes facilitated new sampling and analysis of the buried Madura Shelf sequence that is otherwise obscured by Cenozoic carbonates. The borehole sampled here (FOR011) was drilled at 128.17583°S, 30.61716°E (Fig. 1) to a depth of ~500 m and comprised ~80 m of Cenozoic carbonate disconformably overlying ~205 m of Mesozoic clastics on Forrest Zone crystalline basement of the Coompana Province. Detailed logs were constructed (Fig. DR-2) and palynological and detrital zircon samples (199453) were taken in close proximity from appropriate facies at the top of the Madura Formation (104 m and 98 m depth, respectively). Processed and unprocessed sediment were also examined using BSE electron microscopy and EDS analysis, as well as bulk XRF, in order to assess the preservation of any other compositional indicators of volcanic material. The lack of other distinctive volcanic materials, or the signatures of their breakdown products (devitrification clay products), indicates the sample does not reflect a true tuff horizon but a moderately winnowed (action of shelf currents) sediment with a distinct interval of concentrated Whitsunday-SLIP volcanic zircon delivery. Palynological analysis Palynological processing was undertaken by Morgan Goodall Paleo Pty. Ltd. with standard 100 specimen counts used to resolve species abundance and investigation of other pertinent taxa observed over the entire slide used to resolve biozonation. Mineral separation and preparation One kilogram sediment samples were disaggregated, panned and subjected to heavy liquid separation. Fully representative zircon grains were picked under a binocular microscope and mounted in 25 mm diameter epoxy mounts. Two separate mounts were prepared and polished to half-grain thickness; Mount-1 contained 97 zircon grains, which were imaged using back-scattered-electron (BSE) and cathodoluminescence (CL) electron microscopy under a MIRA3 VP-FESEM at the Microscopy and Microanalysis Facility, John de Laeter Centre, Curtin University before being analyzed using LA-ICPMS for U-Pb geochronology and Hf-isotope geochemistry, Mount-2 contained 160 grains which

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