Uncovering the Musgrave Province in South Australia using airborne EM

Soerensen, Camilla; Munday, Tim; Krapf, Carmen; Love, Andrew J.; Costar, Adrian; Inverarity, Kent; Gogoll, Michael; Gilfedder, Mat

doi:10.1071/aseg2018abt5_3h

Cited by 3 publications

(1 citation statement)

References 4 publications

(5 reference statements)

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“…The AEM data has been released and is downloadable via the South Australian Resources Information Gateway (SARIG). The AEM data, which show the electrical conductivity of the earth up to a depth of several hundred meters, clearly revealed features that correspond to an extensive palaeodrainage network spanning across the APY Lands (Soerensen et al, 2018). Mapping of these palaeodrainage features resulted in an update and refinement of SA's Palaeodrainage dataset (Hou et al, 2012) and also allowed mapping of the thickness of palaeovalley fills and the depth to basement (Sorensen et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Backing up the AEM – unravelling a palaeovalley fill for groundwater exploration in the APY Lands

Krapf

Costar

Keppel³

et al. 2019

ASEG Extended Abstracts

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Section: Introductionmentioning

confidence: 99%

Backing up the AEM – unravelling a palaeovalley fill for groundwater exploration in the APY Lands

Krapf

Costar

Keppel³

et al. 2019

ASEG Extended Abstracts

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Stripping induced polarization effects from airborne electromagnetics to improve 3D conductivity inversion of a narrow palaeovalley

2020

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The electrical conductivity distribution within wide palaeochannels is usually well-mapped from airborne electromagnetic data using stitched 1D algorithms. Such stitched 1D solutions are, however, inappropriate for narrow valleys. An alternative option is to consider 2D or 3D models to allow for finite lateral extent of conductors. In airborne electromagnetic data within the Musgrave block near the well-studied Valen conductor, strong induced polarization (IP) and superparamagnetic (SPM) effects make physical property and structure estimation even more uncertain for deep channel clays, particularly those whose channel widths are comparable to their depth of burial. We developed a recursive data fitting algorithm based on dispersive thin sheet responses. The separate IP and SPM components of the fit provide near-surface chargeability and SPM distributions, and the associated electromagnetic (EM) fit provides stripped data with monotonic decays compatible with a simple nondispersive conductivity model. The validity of this stripped data prediction was tested through a comparison of 1D conductivity-depth imaging and 3D inversion applied to the original data and the stripped data. Due to the forked geometry of the deep conductivity structure in the region we investigated, we successfully used 3D rather than 2D inversion to predict the conductivity distribution related to the EM data. We recovered from the stripped data a continuous conductivity structure consistent with a branching, clay-filled palaeovalley under cover.

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Improving the hydrogeologic conceptualization of a remote semiarid palaeovalley groundwater system using airborne electromagnetics, seismic refraction and reflection, and downhole nuclear magnetic resonance

et al. 2021

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A hydrogeologic conceptualization is critical to understand, manage, protect, and sustain groundwater resources, especially in regions where data are sparse, and accessibility is difficult. We used airborne electromagnetic (AEM), shallow seismic reflection and refraction data, and downhole nuclear magnetic resonance (NMR) logs to improve our understanding of an arid groundwater system influenced by palaeovalleys. In the current hydrogeologic conceptualization it is unknown if the palaeovalley and underlying bedrock aquifers are connected. We focused on defining the spatial distribution of saprolite, which is the layer of chemically altered rock separating the palaeovalley and bedrock aquifers. The AEM data provided an estimate of the top of saprolite but failed to effectively image the bottom. In contrast, the seismic data provided an estimate of the bottom of saprolite but failed to image the top. This unique geophysical combination of electrical and elastic data allowed us to map saprolite thickness in detail along a 1.7 km long transect that runs perpendicular the main trunk of a well-defined palaeovalley. We show that the palaeovalley is lined with a heterogenous layer of saprolite (3-120 m thick) that is thickest near the palaeovalley edges. Despite the variability, only a small percentage of the bedrock aquifer (8-17%) is in contact with the palaeovalley aquifer. Furthermore, the lack of an elastic boundary at the top of saprolite suggests that the porosity of the saprolite is similar to the palaeovalley sediments. An observation that is supported by the downhole NMR water contents. The electrical change at the top of saprolite is caused by a change in pore structure associated with the difference of weathering in situ versus transported materials. Our geophysical data suggest that the saprolite acts as an aquitard limiting groundwater exchange between the palaeovalley and bedrock aquifers.

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Uncovering the Musgrave Province in South Australia using airborne EM

Cited by 3 publications

References 4 publications

Backing up the AEM – unravelling a palaeovalley fill for groundwater exploration in the APY Lands

Backing up the AEM – unravelling a palaeovalley fill for groundwater exploration in the APY Lands

Stripping induced polarization effects from airborne electromagnetics to improve 3D conductivity inversion of a narrow palaeovalley

Improving the hydrogeologic conceptualization of a remote semiarid palaeovalley groundwater system using airborne electromagnetics, seismic refraction and reflection, and downhole nuclear magnetic resonance

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