The ca. 1.4 billion years (Ga) old Roper Group of the McArthur Basin, northern Australia, is one of the most extensive Proterozoic hydrocarbon-bearing basins deposited in a large epeiric sea known as the Roper Seaway. Black shales from the Velkerri Formation were deposited in a deep water shoaling sequence and are well preserved in the Altree 2 drillcore in the Beetaloo Sub-basin. These shales were analysed to determine their organic geochemical (biomarker) signatures which were used to interpret the microbial diversity and palaeoenvironment of the Roper Seaway. The results were integrated with published inorganic geochemistry and microfossil distributions. The indigenous hydrocarbon biomarker assemblages describe a water column dominated by bacteria with large scale heterotrophic reworking of the organic matter in the water column or bottom sediment. Evidence for microbial reworking includes a large unresolved complex mixture (UCM) and high ratios of monomethyl alkanes relative to n-alkanes—features characteristic of indigenous Proterozoic bitumen. Steranes, biomarkers for single-celled and multicellular eukaryotes, were below detection limits in all extracts analysed, despite eukaryotic microfossils having been previously identified in the Roper Group. These data suggest that eukaryotes, while present in the Roper Seaway, were ecologically restricted and contributed little to the net biomass. The combination of increased dibenzothiophene in the middle Velkerri Formation and low concentrations of 2,3,6-trimethyl aryl isoprenoids throughout the Velkerri Formation suggest that the water column at the time of deposition was transiently euxinic. As a comparison we reanalysed extracts from the 1.64 Ga Barney Creek Formation of the McArthur Basin. The biomarker assemblages differ between the Velkerri and Barney Creek Formations between is a biomarkers and water column chemistry, demonstrating that the microbial environments and water column geochemistry were variable in the Proterozoic.

The South Nicholson region, which includes the Paleoproterozoic Isa Superbasin, the Mesoproterozoic South Nicholson Group and overlying younger sediments, is sparsely explored and has recently come into increased focus as a result of the Australian Government’s Exploring for the Future program. Previous exploration has identified potential shale gas plays within the River and Lawn supersequences of the Isa Superbasin in northwest Queensland’s northern Lawn Hill Platform region. Understanding mineralogy is important for characterising shale reservoirs, as mechanical properties such as shale brittleness are influenced by mineral composition. Mineralogy can, therefore, be utilised as a proxy for mechanical properties that are crucial to minimising risks associated with exploring for and developing shale reservoirs. This study utilises three different methods for calculating brittleness; XRD mineralogy, XRF major element geochemistry, and geomechanical properties. Results indicate highly variable mineralogy within the analysed samples, demonstrating heterogeneity in shale brittleness throughout the studied supersequences. Brittleness calculated from XRD analysis ranges from ductile to brittle with zones of brittle shales present in all supersequences. Increasing quartz and decreasing clay content is the dominant control on shale brittleness in the studied samples. Correlation between XRF major element geochemistry and XRD mineralogy is demonstrated to be moderate to poor, with brittleness derived from XRF major element geochemistry observed to be significantly higher than brittleness derived from XRD mineralogy. Conversely, brittleness derived from geomechanical properties agrees closely with XRD mineralogy derived brittleness. Hence, XRF major element geochemistry data are not recommended in the South Nicholson region to calculate brittleness. Analysis of brittleness indices from this study, in combination with total organic carbon content drawn from regional geochemical analysis in the South Nicholson region, identifies potential shale gas target intervals in the River, Term, and Lawn supersequences. Data presented on correlated well sections highlights intervals of exploration interest within these supersequences, being those depths where high organic content, brittle rocks are identified. The rocks that meet this criteria are primarily constrained to the already known potential shale gas plays of the River and Lawn supersequences. Recent data from Geoscience Australia implies that these potential shale gas plays are likely to extend from the northern Lawn Hill Platform, where they have been primarily identified to date, underneath the South Nicholson Basin and into the Carrara Sub-basin, significantly increasing their lateral extent. <b>Citation:</b> A. H. E. Bailey, A. J. M. Jarrett, L. Wang, B. L. Reno, E. Tenthorey, C. Carson & P. Henson (2022) Shale brittleness within the Paleoproterozoic Isa Superbasin succession in the South Nicholson region, Northern Australia, <i>Australian Journal of Earth Sciences, </i>DOI: 10.1080/08120099.2022.2095029

The Exploring for the Future program is an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. As part of the Exploring for the Future program, this study aims to improve our understanding of the petroleum resource potential of northern Australia. This data release presents the bulk kerogen kinetics of 21 potential source rocks from the McArthur Basin and the Lawn Hill Platform to understand the rate of hydrocarbon conversion. Kerogen was isolated from bulk rock, and analysed by a Rock-Eval 6 (Vinci Technologies, France) using four different temperature ramps. All sample preparation and analyses were carried out in Geoscience Australia’s in-house laboratories. The results of this study can be used to improve our understanding of the hydrocarbon generative potential of Proterozoic aged source rocks in northern Australia.

Presentation from the Exploring for the Future Roadshow on the Energy prospectivity of the South Nicholson region, regional geochemical data acquisition and shale gas prospectivity analysis.

Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. The Paleo to Mesoproterozoic Birrindudu Basin is an underexplored frontier basin located in northwestern Northern Territory and northeastern Western Australia. The Birrindudu Basin is a region of focus for the second phase of the EFTF program (2020–2024) as it contains strata of similar age to the prospective McArthur Basin, South Nicholson region and Mount Isa Province, but remains comparatively poorly understood. Geoscience Australia have undertaken (via the service provider, FIT, Schlumberger) stratigraphic reconstructions of bulk volatile chemistry from fluid inclusions from an mineral exploration drillhole LBD2, Birrindudu Basin, located in the northwest Northern Territory This ecat record releases the final report and raw data files (*.LAS) by FIT Schlumberger. Company reference number FI230005a.

The Exploring for the Future Program (EFTF) is a $100.5 million four year, federally funded initiative to better characterise the mineral, energy and groundwater potential of northern Australia. As part of this initiative, this record presents new whole-rock geochemistry data from 967 samples of sedimentary rocks sampled from 26 wells in the South Nicholson region, including the Proterozoic South Nicholson Basin and Lawn Hill Platform, the Neoproterozoic to Devonian Georgina Basin and the Jurassic to Cretaceous Carpenteria Basin. This work complements other components of the EFTF program, including the South Nicholson Basin seismic survey, a comprehensive geochronology program and hydrocarbon prospectivity studies to better understand the geological evolution and basin architecture of the region, and facilitate identification of areas of unrecognised resource potential and prospectivity. The South Nicholson region, straddling north-eastern Northern Territory and north-western Queensland, arguably represents one of the least geologically understood regions of Proterozoic northern Australia. The South Nicholson region is situated between two highly prospective provinces, the greater McArthur Basin in the Northern Territory, the Lawn Hill Platform and the Mount Isa Province in Queensland, both with demonstrated hydrocarbon and base metal potential. These new geochemical data provide baseline understanding of regional resource prospectivity of sedimentary rocks in the South Nicholson region. During 2017 and 2018, 967 drill core and cuttings were sampled from 26 legacy boreholes that intersected the South Nicholson region housed in Northern Territory Geological Survey’s core repository in Darwin, the Geological Survey of Queensland’s core repository in Brisbane and Geoscience Australia’s core repository in Canberra. This data release contains the results of elemental analyses on these samples, which include X-Ray Fluorescence (XRF), Loss-On-Ignition (LOI), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for all samples, in addition to ron titration (FeO) for selected samples. The data was generated in the Inorganic Geochemistry laboratory at Geoscience Australia between 2017 and 2019 as part of the EFTF program. All data was quality controlled based on Certified Reference Material standards (CRMs) and duplicate samples analysed with each batch of samples.

The Proterozoic alkaline and related igneous rocks of Australia web map service depicts the spatial representation of the alkaline and related rocks of Proterozoic age.

NDI Carrara 1 is a deep stratigraphic well completed in 2020 as part of the MinEx CRC National Drilling Initiative (NDI), in collaboration with Geoscience Australia and the Northern Territory Geological Survey. It is the first stratigraphic test of the Carrara Sub-Basin, a newly discovered depocentre in the South Nicholson region. The well intersected Proterozoic sediments with numerous hydrocarbon shows, likely to be of particular interest due to affinities with the known Proterozoic plays of the Beetaloo Sub-basin and the Lawn Hill Platform, including two organic-rich black shales and a thick sequence of interbedded black shales and silty-sandstones. Alongside an extensive suite of wireline logs, continuous core was recovered from 283.9 m to total depth at 1750.8 m, providing high-quality data to support comprehensive analysis. Presently, this includes geochronology, geochemistry, geomechanics, and petrophysics. Rock Eval pyrolysis data demonstrates the potential for several thick black shales to be a source of hydrocarbons for conventional and unconventional plays. Integration of these data with geomechanical properties highlights potential brittle zones within the fine-grained intervals where hydraulic stimulation is likely to enhance permeability, identifying prospective Carrara Sub-basin shale gas intervals. Detailed wireline log analysis further supports a high potential for unconventional shale resources. Interpretation of the L210 and L212 seismic surveys suggests that the intersected sequences are laterally extensive and continuous throughout the Carrara Sub-basin, potentially forming a significant new hydrocarbon province and continuing the Proterozoic shale play fairway across the Northern Territory and northwest Queensland. This abstract was submitted and presented at the 2022 Australian Petroleum Production and Exploration Association (APPEA), Brisbane (https://appea.eventsair.com/appea-2022/)

This record presents a data compilation and thematic maps for existing U–Pb age data for a range of methods and minerals for an area of northern Australia. The compilation includes 2240 age results from the Northern Territory, Queensland and selected areas of South Australia, Western Australia and New South Wales. U–Pb age data was sourced from Geoscience Australia, the Northern Territory Geological Survey, the Geological Survey of Queensland, the Geological Survey of Western Australia and the published scientific literature. Thematic maps have been created from the compiled dataset and show the spatial distribution and age trends of igneous crystallisation ages, maximum depositional ages and metamorphic ages across northern Australia. This work can be used as both a standalone dataset and in conjunction with other geological, geochemical, isotopic and geophysical datasets to better understand the geological evolution of northern Australia.

Exploring for the future presentation- The structure and stratigraphy of the South Nicholson region – implications for resource prospectivity; Insight from the EFTF geochronology and deep reflection seismic programs