The Layered Geology of Australia web map service is a seamless national coverage of Australia’s surface and subsurface geology. Geology concealed under younger cover units are mapped by effectively removing the overlying stratigraphy (Liu et al., 2015). This dataset is a layered product and comprises five chronostratigraphic time slices: Cenozoic, Mesozoic, Paleozoic, Neoproterozoic, and Pre-Neoproterozoic. As an example, the Mesozoic time slice (or layer) shows Mesozoic age geology that would be present if all Cenozoic units were removed. The Pre-Neoproterozoic time slice shows what would be visible if all Neoproterozoic, Paleozoic, Mesozoic, and Cenozoic units were removed. The Cenozoic time slice layer for the national dataset was extracted from Raymond et al., 2012. Surface Geology of Australia, 1:1 000 000 scale, 2012 edition. Geoscience Australia, Canberra.

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This study was undertaken to establish a chronology for Quaternary fluvial landscape in the Darling River floodplain area. This was required to constrain the 3D mapping of floodplain units and to constrain conceptual models of surface-groundwater interaction. The lower Darling Valley contains Cenozoic shallow marine, fluvial, lacustrine and aeolian sediments including a number of previously poorly dated Quaternary fluvial units associated with the Darling River and its anabranches. New geomorphic mapping of the Darling floodplain that utilises a high-resolution LiDAR dataset and SPOT imagery, has revealed that the Late Quaternary sequence consists of scroll-plain tracts of different ages incised into a higher more featureless mud-dominated floodplain. Furthermore, the Understanding the relationships between these geomorphic units Samples for OSL (Optically-Stimulated Luminescence) and radiocarbon dating were taken in tractor-excavated pits, from sonic drill cores and from hand-auger holes from a number of scroll-plain and older floodplain sediments in the Menindee region. The youngest, now inactive, scroll-plain phase, associated with the modern Darling River, was active in the period 5-2 ka. A previous anabranch scroll-plain phase has dates around 20 ka. Indistinct scroll-plain tracts older than the anabranch system, are evident both upstream and downstream of Menindee and have ages around 30 ka. These three scroll-plain tracts intersect just south of Menindee but are mostly separated upstream and downstream of that point. Older dates of 50 ka, 85 ka and >150 ka have been obtained from lateral-migration sediments present beneath the higher mud-dominated floodplain. Age dating of the Quaternary fluvial sediments has been used to constrain a model of landscape evolution, neotectonics and recharge dynamics. Geomorphic and structural mapping identified a number of structural lineaments in the LiDAR data. These structures are coincident with mapped faults at depth in airborne electromagnetic (AEM) and airborne magnetic (and gravity) data. Those faults mapped at surface have varying landscape expression, with many re-worked by younger scroll-plain tracts. Younger faults appear to play a role in surface-groundwater interaction, while older faults are important for inter-aquifer leakage.

In this study, a multi-disciplinary systems mapping approach has completely revised our understanding of the age, stratigraphy, mode of deposition and landscape evolution of Lower Darling Valley (LDV) sediments within the north-western Murray Basin. The Cenozoic sequence in this area contains Paleogene and Neogene shallow marine, fluvial and shoreline sediments overlain by Quaternary lacustrine, aeolian and fluvial units. The surficial Quaternary fluvial units of the valley form a complex group of morphostratigraphic units which vary in their distribution, character and geomorphic expression through the study area. Resolving the distribution of these units has been particularly important for understanding surface-groundwater interactions. In the LDV Quaternary fluvial sequence, multiple scroll-plain tracts are incised into higher, older more featureless floodplains. Prior to this study, these were respectively correlated to the Coonambidgal and Shepparton Formations of the Riverine Plain in the eastern Murray Basin and associated with the subsequently discarded Prior Stream/Ancestral River chronosequence of different climatically controlled depositional styles. In contrast to that proposition, we ascribe all LDV Quaternary fluvial deposition to lateral-migration depositional phases of one style, though with more variable stream discharges and channel and meander-scroll dimensions. Successively higher overbank-mud deposition through time obscures scroll traces and provides the main ongoing morphologic difference. A new morphostratigraphic unit, the Menindee Formation, refers to the mostly older and higher floodplain sediments, where scroll traces are obscured by overbank mud which continues to be deposited by the highest modern floods. Younger inset scroll-plain tracts, with visible scroll-plain traces, are still referred to the Coonambidgal Formation. Another new stratigraphic unit, the Willotia beds, refers to even older fluvial sediments, now above modern floodplain levels and mostly covered by aeolian sediments. This work provides important insights into the nature of Australian Quaternary fluvial deposition, with important implications for hydrogeological processes, groundwater resources and the assessment of managed aquifer recharge options.

This study of drillcore materials was carried out to assess the ability of hyperspectral methods to rapidly map the distribution of key minerals pertinent to managed aquifer recharge studies in the Darling floodplain. The study used two hyperspectral instruments: the Hylogger core scanner (using an instrument at DMITRE Minerals in Adelaide); and the Portable Infrared Mineral Analyser (PIMA). Further validation of the methods was carried out using XRD analysis of selected samples. Cores were obtained using the sonic drilling method. The Hylogger tool qualitatively mapped the distribution of clays and oxides in both the confining aquitard and key aquifers. The unconfined Coonambidgal Formation aquifer is dominated by montmorillonite, and the Blanchetown Clay aquitard by kaolinite with lesser montmorillonite. Clay mineralogy in the Calivil Formation aquifer is related to sedimentary facies, with kaolinite and lesser nontronite in muddy units, and kaolinite-dominant or smectite-dominant clays in sandy units. The two clay mineral associations were found to correlate with different hydraulic conductivity trends in the NMR data from the aquifer. These trends have been defined by the Kernel Function of Nuclear Magnetic Resonance (NMR)-derived hydraulic conductivity data. Kernel Functions (C values) of 6,200 corresponding with predominantly smectites in the screened aquifer interval, and C values of 46,000 corresponding with kaolinite in the screened aquifer intervals of two holes. This made it possible to predict the dominant clay in the screened aquifer intervals in the remaining NMR-logged holes. These predictions were tested using PIMA analysis of the clay mineralogy of addition from NMR-logged holes. Of 97 PIMA scans, 67 contained the predicted mineralogy and 27 did not, giving a success rate of 69%, providing reasonable confidence that the Kernal Function in the NRM logging can be explained by the clay mineralogy. Overall, this study demonstrates that hyperspectral logging can provide relatively rapid, semi-quantitative data on the abundance and distribution of clay and oxide mineralogy in drillcore. These data assisted with geochemical modelling and risk assessments at the Jimargil aquifer storage and recovery (ASR) site.

1st edition Available as a product from NT Geological Survey or as a resource from GA Library