Energy potential of the Millungera Basin: a newly discovered basin in north Queensland

Abstract

Deep seismic reflection surveys in north Queensland that were collected in 2006 and 2007 discovered a previously unknown sedimentary basin, now named the Millungera Basin, which is completely covered by a thin succession of sediments of the Jurassic–Cretaceous, Eromanga-Carpentaria Basin. Interpretation of regional aeromagnetic data suggests that the basin could have areal dimensions of up to 280 km by 95 km. Apart from regional geophysical data, virtually no confirmed geological information exists on the basin. To complement the seismic data, new magnetotelluric data have been acquired on several lines across the basin. An angular unconformity between the Eromanga and Millungera basins indicates that the upper part of the Millungera Basin was eroded prior to deposition of the Eromanga-Carpentaria Basin. Both the western and eastern margins of the Millungera Basin are truncated by thrust faults, with well-developed hangingwall anticlines occurring above the thrusts at the eastern margin. The basin thickens slightly to the east, to a maximum preserved subsurface depth of ˜3,370 m. Using sequence stratigraphic principles, three discrete sequences have been mapped. The geometry of the stratigraphic sequences, the post-depositional thrust margins, and the erosional unconformity at the top of the succession all indicate that the original succession across much of the basin was thicker–by up to at least 1,500 m–than preserved today. The age of the Millungera Basin is unknown, but petroleum systems modelling has been carried out using two scenarios, that is, that the sediment fill is equivalent in age to (1) the Neoproterozoic-Devonian Georgina Basin, or (2) the Permian–Triassic Lovelle Depression of the Galilee Basin. Using the Georgina Basin analogue, potential Cambrian source rocks are likely to be mature over most of the Millungera Basin, with significant generation and expulsion of hydrocarbons occurring in two phases, in response to Ordovician and Cretaceous sediment loading. For the Galilee Basin analogue, potential Permian source rocks are likely to be oil mature in the central Millungera Basin, but immature on the basin margins. Significant oil generation and expulsion probably occurred during the Triassic, in response to late Permian to Early Triassic sediment loading. Based on the seismic and potential field data, several granites are interpreted to occur immediately below the Millungera Basin, raising the possibility of hot rock geothermal plays. Depending on its composition, the Millungera Basin could provide a thermal blanket to trap any heat which is generated. 3D inversion of potential field data suggests that the inferred granites range from being magnetic to nonmagnetic, and felsic (less dense) to more mafic. They may be part of the Williams Supersuite, which is enriched in uranium, thorium and potassium, and exposed just to the west, in the Mount Isa Province. 3D gravity modelling suggests that the inferred granites have a possible maximum thickness of up to 5.5 km. Therefore, if granites with the composition of the Williams Supersuite occur beneath the Millungera Basin, in the volumes indicated by gravity inversions, then, based on the forward temperature modelling, there is a good probability that the basin is prospective for geothermal energy.

Precambrian faulting episodes and insights into the tectonothermal history of North Australia: Microstructural evidence and K–Ar, <sup>40</sup>Ar–<sup>39</sup>Ar, and Rb–Sr dating of syntectonic illite from the intracratonic Millungera Basin

“…The radiogenic initial 87 Sr/ 86 Sr ratios of about 0.72 indicate the involvement of fluids that equilibrated with old Rb-rich crustal rocks. The trace element and Sr isotope data are in agreement with seismic and potential field data by Korsch et al (2011), which is interpreted as indicating the occurrence of granites with a thickness up to 5.5 km below the Millungera Basin. The inferred granites may be a part of the granite (Williams Supersuite) exposed just to the west in the Mt Isa Inlier, which is enriched in Th, U, and K (Korsch et al, 2011 and references therein).…”

“…It occurs to the east of the Paleoproterozoic Mount Isa Province and is covered by the thin Jurassic-Cretaceous Eromanga-Carpentaria Basin. An angular unconformity between the Eromanga and Millungera Basins indicates that the upper part of the Millungera Basin was eroded prior to deposition of the Eromanga-Carpentaria Basin (Korsch et al, 2011), allowing sampling of the deeper part of the basin, which is strongly deformed and faulted (see below). Interpretation of aeromagnetic data suggests that the basin might have a real dimension of up to 280 km by 95 km (Korsch et al, 2011).…”

“…Prior to this study ( Fig. 1), almost no geological information was available on the Precambrian geology of large parts of north-central Australia, including the Millungera Basin, except for some regional geophysical data (Korsch et al, 2011(Korsch et al, , 2012 (Fig. 1).…”

“…Further uncertainties in tectonic interpretation of Australian Precambrian terranes arises from the tendency for original tectonic information to be masked by younger tectonics. Therefore, a major objective of this study was to provide insight into the enigmatic time-space distribution of Mid-to Late-Mesoproterozoic tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant potential for energy and mineral resources (Korsch et al, 2011(Korsch et al, , 2012.…”

Crustal architecture and geodynamics of North Queensland, Australia: Insights from deep seismic reflection profiling

“…The Millungera Basin overlies four prominent nonreflective zones up to 0.5 s TWT (1.5 km) thick, which we interpret to be granites. For a detailed description of the Millungera Basin, see Korsch et al (2011). Further to the northeast, a series of reflections with a similar sedimentary character occur at about CDP 16400 to about CDP 17000 and are possibly part of the same basin system.…”