Catchment-scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing; they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant. However, in many cases, such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components, particularly in regions dominated by cycles of droughts and flooding. From a modelling perspective, such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems. In this study, we use 3D geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the Lockyer Valley (Queensland, Australia), a catchment impacted by a severe drought (‘Millennium Drought’) from 1998 to 2009, followed by extensive flooding in 2011. We also demonstrate how discharge from the sub-alluvial regional-scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams. The investigation of aquifer geometry via development of a three-dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams. Multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets. This confirmed that most sub-catchments within the Lockyer Valley have distinct water chemistry patterns, which result from mixing of different water sources, including discharge from the sub-alluvial bedrock. Importantly, in addition to the observed spatial variability, time-series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers, streams and sub-alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding, affecting both catchment water quality and water balances. <b>Citation:</b> M. Raiber, S. Lewis, D.I. Cendón, T. Cui, M.E. Cox, M. Gilfedder, D.W. Rassam, Significance of the connection between bedrock, alluvium and streams: A spatial and temporal hydrogeological and hydrogeochemical assessment from Queensland, Australia, <i>Journal of Hydrology</i>, Volume 569, 2019, ISSN 0022-1694, https://doi.org/10.1016/j.jhydrol.2018.12.020.

The Great Artesian Basin (GAB), a hydrogeological entity that contains predominantly the Jurassic-Cretaceous Eromanga, Surat and Carpentaria geological basins, is the largest groundwater basin in Australia. It underlies one fifth of the continent, including parts of Queensland, New South Wales, South Australia and the Northern Territory. Groundwater from the GAB is a vital resource for agricultural and extractive industries, as well as for community water supply. It supports cultural values and sustains a range of groundwater-dependent ecosystems. Water managers from each jurisdiction regulate GAB resources using hydrogeological conceptualisations based on a diverse historical geoscientific nomenclature that is often unique to a jurisdiction. However, the basin and its resources are continuous across borders, and recent studies have shown high spatial variability in the hydrostratigraphic units across the basin. There is, therefore, a clear need to map the geological complexity consistently at a basin-wide scale in order to provide a hydrogeological framework to underpin effective long-term management of GAB water resources. The present study is part of the Australian Government funded project ‘Assessing the Status of Groundwater in the Great Artesian Basin’ to refine the basin conceptualisation and water balance estimates (Figure 1.1). This study focuses on an updated GAB hydrogeological architecture by compiling and standardising existing and newly interpreted biostratigraphic and well formation picks from geological logs, 2D seismic and airborne electromagnetic data in a consistent chronostratigraphic framework. This framework is used to correlate geological units across the GAB. The basin-wide correlation identifies age-equivalent sediments in different depositional settings encompassing transgressive and regressive phases. Biostratigraphic control using a common unified zonation scheme is used to identify lithological correlations. Rock properties are attributed based on sediment facies deposited during similar geological events. The approach provides a consistent way of mapping the distribution and properties of aquifers and aquitards across the GAB. In particular, the refined correlation of Jurassic and Cretaceous units between the Surat and Eromanga basins improves the resolution of hydrogeological unit geometry and lithological variation that may influence groundwater flow within and between aquifers. The 3D hydrogeological architecture developed provides a model for refining hydrogeological conceptualisations and assists in revising GAB water balance estimates. Key findings are: • The new 3D model of the GAB extends the connectivity of aquifers across the entire GAB, with potential implications for jurisdictional groundwater management. For example, the Adori Sandstone, which was previously mapped largely in the central and eastern Eromanga Basin, potentially has connectivity with the time-equivalent Springbok Sandstone in the Surat Basin across the boundary between the two basins (the Nebine Ridge). Coincident with the Nebine Ridge is a groundwater divide that tends to segregate groundwater flow between the two basins. However, cumulative impacts from excessive pumping could cause the groundwater divide to migrate due to the continuation of sandstone unit (and connectivity) across the Nebine Ridge. In addition, the Adori Sandstone is connected with the time-equivalent Algebuckina Sandstone found towards the western margin of the Eromanga Basin, which suggests there is potential for connectivity from basin margin to basin centre. This key finding improves estimates of volume and distribution of sandstone of this aquifer across all GAB jurisdictions. • The extent of other hydrogeological units have also been refined. For instance the Cadna-owie-Hooray aquifer of Ransley et al. (2015) is now separated into two units 1. Murta Formation/Hooray–Namur–Mooga sandstones aquifer and the 2. Cadna-owie–Bungil formation and equivalents aquifer. The updated mapping highlights that the upper Cadna-owie‒Bungil‒Wyandra aquifer extends across the whole GAB, and is potentially confined by the underlying Murta and lower Cadna-owie‒Bungil aquitards and overlying Rolling Downs aquitard. Higher resolution mapping of sub-units within the Cadna-owie–Bungil–Hooray and equivalents aquifer provides an improved understanding of lithological variability and the potential compartmentalisation of groundwater that may be isolated from from regional flow paths (i.e. ‘dead ends’). The lithological variability mapping within hydrogeological units highlights zones of potential connectivity where leakage may occur between the deeper and shallower aquifers, affecting upward loss of groundwater from GAB aquifers in areas distal to the outcropping recharge beds. • The new lithology mapping also highlights that the Birkhead and Westbourne formations, classified as interbedded aquitard and tight aquitard, respectively, in the Eromanga Basin, correlate laterally with time-equivalent intervals within the Algebuckina Sandstone aquifer, suggesting connection between the Hutton, Adori and Namur‒Hooray aquifers across the central and western Eromanga Basin. • The new 3D model updates hydrogeological conceptualisations in the GAB and improves groundwater balance estimates for the GAB (Ransley et al., 2022.). It is also used to constrain a regional-scale groundwater flow dynamics model for the region, including uncertainty analysis within a Bayesian framework (Knight et al., 2022). This aspect of the study is assessing a powerful approach for solving non-unique inverse problems in terms of quantifying model uncertainty. This is crucial in providing a context for, and awareness of, uncertainties in system conceptualisation that need to be accounted for, or at least acknowledged up front. • This study compiles, collates and integrates existing and newly acquired geoscientific data characterising Jurassic Cretaceous geological units that represent the hydrostratigraphy of the GAB. The updated stratigraphy improved correlations between the Eromanga, Surat and Carpentaria basins leading to better hydrogeological interpretations at the whole of GAB scale. The work draws upon the results of other recent studies to gain new insights into the geological architecture and depositional history, which have implications for groundwater occurrence and flow within and between key GAB aquifers. This updated understanding has basin-wide implications for water management, and plays a key role in revising water balance estimates for the whole GAB. The chronostratigraphic approach used here can be applied at a national scale to correlate consistently hydrostratigraphic units, providing a broader context for groundwater systems assessments.

<div>As part of the Australia's Resources Framework Project, in the Exploring for the Future Program, Geoscience Australia and CSIRO have undertaken a magnetic source depth study across four areas. These are: 1) the western part of Tasmania that is the southernmost extension of the Darling-Curnamona-Delamerian (DCD) project area; 2) northeastern Queensland; 3) the Officer Basin area of western South Australia and southeastern West Australia; and 4) the 'Eastern Resources Corridor' (ERC) covering eastern South Australia, southwest Queensland, western New South Wales and western Victoria. This study has produced 2005 magnetic estimates of depth to the top of magnetization. The solutions are derived by a consistent methodology (targeted magnetic inversion modelling, or TMIM; also known as ‘sweet-spot’ modelling). </div><div><br></div><div>The magnetic depth estimates produced as part of this study provide depth constraints in data-poor areas. They help to construct a better understanding of the 3D geometry of the Australian continent, and aid cover thickness modelling activities. </div><div><br></div><div>A supplementary interpretation data release is also available through Geoscience Australia's enterprise catalogue (ecat) at https://pid.geoscience.gov.au/dataset/ga/149499.</div><div><br></div><div>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. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government. This work contributes to building a better understanding of the Australian continent, whilst giving the Australian public the tools they need to help them make informed decisions in their areas of interest.</div>

Geoscience Australia’s regional assessments and basin inventories are investigating Australia’s groundwater systems to improve knowledge of the nation’s groundwater potential under the Exploring for the Future (EFTF) Program and Geoscience Australia’s Strategy 2028. Where applicable, integrated basin analysis workflows are being used to build geological architecture advancing our understanding of hydrostratigraphic units and tie them to a nationally consistent chronostratigraphic framework. Here we focus on the Great Artesian Basin (GAB) and overlying Lake Eyre Basin (LEB), where groundwater is vital for pastoral, agricultural and extractive industries, community water supplies, as well as supporting indigenous cultural values and sustaining a range of groundwater dependent ecosystems such as springs and vegetation communities. Geoscience Australia continued to revise the chronostratigraphic framework and hydrostratigraphy for the GAB infilling key data and knowledge gaps from previous compilations. In collaboration with Commonwealth and State government agencies, we compiled and standardised thousands of boreholes, stratigraphic picks, 2D seismic and airborne electromagnetic data across the GAB. We undertook a detailed stratigraphic review on hundreds of key boreholes with geophysical logs to construct consistent regional transects across the GAB and LEB, using geological time constraints from hundreds of boreholes with existing and newly interpreted biostratigraphic data. We infilled the stratigraphic correlations along key transects across Queensland, New South Wales, South Australia and Northern Territory borders to refine nomenclature and stratigraphic relationships between the Surat, Eromanga and Carpentaria basins, improving chronostratigraphic understanding within the Jurassic to Cretaceous units. We extended the GAB geological framework to the overlying LEB to better resolve the Cenozoic stratigraphy and potential hydrogeological connectivity. New data and information fill gaps and refine the previous 3D hydrogeological model of the entire GAB and LEB. The new 3D geological and hydrostratigraphic model provides a framework to integrate additional hydrogeological and rock property data. It assists in refining hydraulic relationships between aquifers within the GAB and provides a basis for developing more detailed hydrogeological system conceptualisations. This is a step towards the future goal of quantifying hydraulic linkages with underlying basins, and overlying Cenozoic aquifers to underpin more robust understanding of the hydrogeological systems within the GAB. This approach can be extended to other regional hydrogeological systems. This Abstract was submitted/presented at the 2023 Australasian Exploration Geoscience Conference (AEGC) 13-18 March (https://2023.aegc.com.au/)

<div>This dataset presents results of a first iteration of a 3D geological model across the Georgina Basin, Beetaloo Sub-basin of the greater McArthur Basin and South Nicholson Basin (Figure 1), completed as part of Geoscience Australia’s Exploring for the Future Program National Groundwater Systems (NGS) Project. These basins are located in a poorly exposed area between the prospective Mt Isa Province in western Queensland, the Warramunga Province in the Northern Territory, and the southern McArthur Basin to the north. These surrounding regions host major base metal or gold deposits, contain units prospective for energy resources, and hold significant groundwater resources. The Georgina Basin has the greatest potential for groundwater.</div><div>&nbsp;</div><div>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. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government. More information is available at http://www.ga.gov.au/eftf and https://www.eftf.ga.gov.au/national-groundwater-systems.</div><div>&nbsp;</div><div>This model builds on the work undertaken in regional projects across energy, minerals and groundwater aspects in a collection of data and interpretation completed from the first and second phases of the EFTF program. The geological and geophysical knowledge gathered for energy and minerals projects is used to refine understanding of groundwater systems in the region.</div><div>&nbsp;</div><div>In this study, we integrated interpretation of a subset of new regional-scale data, which include ~1,900 km of deep seismic reflection data and 60,000 line kilometres of AusAEM1 airborne electromagnetic survey, supplemented with stratigraphic interpretation from new drill holes undertaken as part of the National Drilling Initiative and review of legacy borehole information (Figure 2). A consistent chronostratigraphic framework (Figure 3) is used to collate the information in a 3D model allowing visualisation of stacked Cenozoic Karumba Basin, Mesozoic Carpentaria Basin, Neoproterozoic to Paleozoic Georgina Basin, Mesoproterozoic Roper Superbasin (including South Nicholson Basin and Beetaloo Sub-basin of the southern McArthur Basin), Paleoproterozoic Isa, Calvert and Leichhardt superbasins (including the pre-Mesoproterozoic stratigraphy of the southern McArthur Basin) and their potential connectivity. The 3D geological model (Figure 4) is used to inform the basin architecture that underpins groundwater conceptual models in the region, constrain aquifer attribution and groundwater flow divides. This interpretation refines a semi-continental geological framework, as input to national coverage databases and informs decision-making for exploration, groundwater resource management and resource impact assessments.</div><div><br></div><div>This metadata document is associated with a data package including:</div><div>·&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Nine surfaces (Table 1): 1-Digital elevation Model (Whiteway, 2009), 2-Base Cenozoic, 3-Base Mesozoic, 4-Base Neoproterozoic, 5-Base Roper Superbasin, 6-Base Isa Superbasin, 7-Base Calvert Superbasin, 8-Base Leichhardt Superbasin and 9-Basement.</div><div>·&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Eight isochores (Table 4): 1-Cenozoic sediments (Karumba Basin), 2-Mesozoic sediments (Carpentaria and Eromanga basins), 3-Paleozoic and Neoproterozoic sediments (Georgina Basin), 4-Mesoproterozoic sediments (Roper Superbasin including South Nicholson Basin and Beetaloo Sub-basin), 5-Paleoproterozoic Isa Superbasin, 6-Paleoproterozoic Calvert Superbasin, 7-Paleoproterozoic Leichhardt Superbasin and 8-Undifferentiated Paleoproterozoic above basement.</div><div>·&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Five confidence maps (Table 5) on the following stratigraphic surfaces: 1-Base Cenozoic sediments, 2-Base Mesozoic, 3-Base Neoproterozoic, 4-Base Roper Superbasin and 5-Combination of Base Isa Superbasin/Base Calvert Superbasin/Base Leichhardt Superbasin/Basement.</div><div>·&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Three section examples (Figure 4) with associated locations.</div><div>Two videos showing section profiles through the model in E-W and N-S orientation.</div>