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The enigmatic sub-surface Tookoonooka Complex in south-west Queensland: its impact origin and implications for hydrocarbon accumulations
Abstract
The sub-surface Tookoonooka structure has been variously described as an astrobleme, or a complex volcanic caldera. However, the concentric arrangement of anticlines and synclines, the raised central core of Early Palaeozoic metamorphic sediments coinciding with a gravity low, the presence of a radial, saucer-shaped disruption boundary separating normal Eromanga succession below from highly disrupted fallback breccia above, plus petrographic evidence of both glass matrix and fragments, and shock lamellae in quartz grains within the fallback breccia are all diagnostic of Tookoonooka being of impact origin.
... The impact origin of subsurface structures is notoriously difficult to investigate due to inaccessibility and paucity of data. Tookoonooka was confirmed as an impact structure through the identification and measurement of shock metamorphic features in quartz grains (Gorter et al. 1989;Gostin and Therriault 1997) from the structure's buried central uplift. However, Talundilly has not been adequately drilled to date, and remains a possible impact structure. ...
... Tookoonooka is the second-largest known impact structure in Australia, and possibly the tenth largest in the world (Earth Impact Database, 2011). It was estimated to have a final crater diameter of 66 km (Gostin and Therriault 1997), which is a recalculation of an earlier estimate of 55 km from seismic data (Gorter et al. 1989). Talundilly was estimated to have a 95 km diameter from seismic data (Longley 1989). ...
... Based on their similar stratigraphic positions, the two structures are thought to be the result of a binary impact event (Gorter 1998;Haines 2005). From palynology and seismic stratigraphic interpretations, the age of the impact event has been variously estimated at approximately 128 Ma between palynostratigraphic units PK2.1 and PK2.2 (Gorter et al. 1989;Gostin and Therriault 1997), and between 112 and 115 Ma (Gorter 1998), within the Lower Cretaceous (Fig. 2). Bron (2010) constrained the impact age to 125 ± 1 Ma based on a first presence of impactoclasts in the stratigraphy. ...
Ejecta from the large subsurface Tookoonooka impact structure have been found
in the Lower Cretaceous strata of the extensive Eromanga Basin of central
Australia. Observations from 31 wells spanning 400,000 km2 of the basin provide compelling
evidence for the presence of a marine impact horizon of regional extent. Drill core was
examined to determine the sedimentary context of the Tookoonooka impact event, the
presence of ejecta, and the nature of the impact horizon. The base of the Wyandra Sandstone
Member of the Cadna-owie Formation is an unconformity commonly overlain by very poorly
sorted sediment with imbricated pebbles, exotic clasts, and occasional boulders. The basal
Wyandra Sandstone Member is bimodal: a fine sand mode reflects an ambient sediment
contribution and a coarse mode is interpreted to be impact-derived. Wells Thargomindah-1
and Eromanga-1, within four crater radii of Tookoonooka, contain distinctive clastsupported
breccia-conglomerate beds at the base of the Wyandra Sandstone Member. Clasts
in these beds include altered accretionary and melt impactoclasts, as well as lithic and mineral
grains corresponding to the Tookoonooka target rock sequence, including basement.
Petrographic evidence includes shock metamorphosed quartz and lithic grains with planar
deformation features. These breccia-conglomerates are in stark contrast to the underlying,
laterally persistent, unimodal Cadna-owie sediments and overlying shales deposited in an
epeiric sea. The base of the Wyandra Sandstone Member is therefore interpreted to be the
Tookoonooka impact horizon. The timing of the impact event is confirmed to be the
Barremian-Aptian boundary, at 125 ± 1 Ma. The Wyandra Sandstone Member preserves
both impact ejecta and postimpact marine sediments.
... A characteristic of the Tookoonooka region is the absence of the 'C' seismic horizon in a roughly circular region centred on the basement high in the middle of the structure ). The well log correlation shown in figure 10 of Gorter et al. (1989) shows that the low interval velocity zone at the base of the Bulldog Shale is also missing at GSQ Thargomindah-3 and Toucaria-1, located within the area in which the 'C' seismic horizon is missing. Clearly, the absence of the 'C' seismic horizon is associated with the lack of the low velocity zone characteristic of the Cadna-Owie Formation to Bulldog Shale transition over much of the Eromanga Basin. ...
... The Talundilly-1 well is located neither near the centre of the seismic anomaly (compare figure 5 of Gorter et al. 1989 with figure 12 of Longley 1989) nor on the apex of the aeromagnetic high ( Figure 5). Consequently, assuming that both wells were drilled on impact structures, the more centrally located Tookoonooka-1 well intersection is more likely to intersect evidence of impact, such as the disrupted pre-event section shown on the down hole logs (Figure 3), than Talundilly-1, which is located more distally from the interpreted central high (Longley 1989, figure 11) and penetrated a near-standard pre-event stratigraphy ( Figure 3). ...
... Samples which display PDFs were derived from Tookoonooka-1 at 906 metres depth (C44474 Tookoonooka-1 23). The horizon lies between the Aptian age O. operculata dinoflagellate zone (lower C. hughesii spore-pollen zone and lower APK3.1 spore-pollen zone of early Aptian age in Figure 2) and the C. australiensis palynological zone (APK1 spore-pollen zone of Berriasian-Valanginian age in Figure 2) (Hos & Islam 1984;Morgan 1985;Gorter et al. 1989, figure 10). The closely comparable log correlation between Talundilly-1 and Tookoonooka-1 suggests that the equivalent strati-graphic horizon lies between 1000 and 1100 m, probably about 1025 m (Figure 3), although no palynological dating exists for the Talundilly-1 intersection. ...
The Talundilly Structure, southwestern Queensland, Australia, is represented on 2D seismic reflection transects as a major seismic anomaly disrupting the consistent ‘C’ seismic–stratigraphic horizon above the early Cretaceous Bulldog Wallumbilla Formation throughout the Eromanga Basin. The seismic anomalous zone, estimated at 84 km in diameter from the maximum extent of horizon disruption, coincides with a prominent aeromagnetic (TMI) high which is centrally located within a near-circular seismic anomaly of the ‘C’ horizon. The structure consists of a raised central area, with radial faults extending from the central high, an annular synform with disrupted seismic elements dipping at low angles towards the central uplift, and an outer faulted rim. Cuttings from the Talundilly-1 well, drilled ∼30 km northwest from the central high, contain quartz grains with planar deformation features (PDF) indicative of shock metamorphism. The age of the structure, as determined from seismic correlation and sparse palynology, post-dates the ‘C’ seismic horizon and is determined as approximately 125 Ma, coinciding with a marine transgression. Correlation of seismic profiles suggest that the Talundilly impact structure is a possible twin of the Tookoonooka impact structure, dated as 125 ± 1 Ma and located 328 km to the south.
... Summary Layer bound polygonal faults are present within Cretaceous Eromanga Basin marine sediments across the entire basin (Heath et al., 1989;Kulikowski, 2017;Kulikowski & Amrouch, 2017;Kulikowski, Amrouch, Cooke, & Gray, 2018;Watterson et al., 2000). These faults were first identified from 2D seismic data (Gilby & Mortimore, 1989;Gorter et al., 1989;Longley, 1989;Moore & Pitt, 1984;Newton, 1986;Rumph, 1982;Scholefield, 1989;Young et al., 1989), with the 3D distribution and regional extent described more recently (Kulikowski, 2017;Kulikowski, Amrouch, Cooke, & Gray, 2018;Oldham & Gibbins, 1995;Watterson et al., 2000). A detailed analysis of polygonal faults within the Lake Hope 3D seismic survey suggests that their development is linked to a density inversion, where a low density and overpressured stratal unit was buried and dewatered by overlying normally pressured and higher density sediments (Watterson et al., 2000). ...
This review focuses on integrating old literature with present-day models to provide a modern summary of Australia’s largest onshore hydrocarbon province, the Cooper–Eromanga Basin, with a focus on structural geology and geophysics. A rapid rise in cutting-edge research has been facilitated by hydrocarbon companies transitioning to technically more challenging plays and feasibility studies assessing the carbon capture and storage potential of the basin. The purpose of this review is to provide researchers and new and existing operating companies with an integrated summary of recent research and the fundamentals of the structurally complex basin with the aim of ensuring that the hydrocarbon potential can be effectively explored and appropriately developed, and that the carbon capture and storage potential of the basin is appropriately evaluated. A modern tectonostratigraphic evolution model is presented alongside the stress regime, orientation and magnitude of the six events that have affected the province (N–S Carboniferous Alice Springs Orogeny; SE–NW mid-Permian event; NE–SW late Permian Daralingie event; E–W Triassic Hunter–Bowen Event; E–W Late Cretaceous event; N–S Paleogene event). Integration of complete paleo-stress tensors with geomechanical models has constrained the dynamic reactivation (shear and tensile) of faults through time and space to find that since the critical time (90 Ma), N–S- and E–W-striking high-angle (50–70°) faults were most likely facilitating hydrocarbon migration. These form the major topics of the review as they can significantly impact exploration and development success and effective carbon capture and storage. In addition, the four-dimensional distribution of natural fractures away from the wellbore, seismic time-to-depth conversion methods and accuracies, petroleum systems elements and processes, current and future exploration programs, common hydraulic fracturing and well surveillance programs, and recommendations for future research are also discussed. The methodologies, cutting-edge research and novel approaches presented here form a framework that can be applied to other hydrocarbon provinces around the world, while also providing a knowledge platform for this highly prospective hydrocarbon and potential carbon storage province.
• KEY POINTS
• Comprehensive modern literature review of the Cooper–Eromanga Basin.
• Integration of geophysics, geology and reservoir engineering to form a holistic synthesis of Australia’s largest onshore hydrocarbon province.
• Insights into the interaction between hydrocarbon migration and basin evolution.
... Seismic reflection and refraction measurements provide complementary information to potential-field data and geological observations on the characteristics of terrestrial impact structures. Reflection surveys, especially in sedimentary targets, allow for detailed imaging of the crater morphology, and for delineating seismically isotropic zones and incoherent reflections that are characteristic of brecciation and fracturing (Gorter et al., 1989;Grieve and Pilkington, 1996). For example, detailed information on the near surface structure of the Ries crater, where the target is sedimentary rock, has been obtained by seismic reflection measurements (Angenheister and Pohl, 1969). ...
Geophysical investigations have been carried out at the Bosumtwi impact crater in Ghana to determine the geophysical characteristics that are related to the impact process. Gravity, magnetic and wide angle seismic reflection and refraction studies have been used to obtain information on the impact-related anomalies. Seismic modelling gave a three layer model of the crater consisting of the water layer with a velocity of 1.45 km/s, post-impact sediments with low velocities of 1.50-1.65 km/s and a third layer which is referred to as the crater floor made up of basement rocks. Seismic velocities were found to increase from 2.8 km/s at the interface of post-impact sediments and crater floor to about 5 km/s in 1.6 km depth. The central uplift, which confirms the Bosumtwi crater as a complex impact crater, was found to be 250 m below the water surface. The velocity of 2.8 km/s is interpreted to be due to fallback breccia which completely covered the central uplift. Gravity measurements yielded a maximum negative anomaly of 18 mgal over the crater. This is interpreted to be caused by fractured and brecciated rocks in the rim area and below the crater floor, breccias within the crater, and sedimentary and water infilling of the lake. Magnetic modelling showed that the magnetized bodies are found to be located between 250 and 610 m depths
... An impact event was described for the Early Cretaceous (Barremian) of Australia. The impact structure is known as the Tookoonooka crater, a huge (~60 km diameter) astrobleme discovered by seismic surveys (Gorter et al., 1989). ...
The Mesozoic was the time of the break-up of Pangaea, with profound consequences not only for the paleocontinental configuration, but also for paleoclimates and for the evolution of life. Cool greenhouse conditions alternated with warm greenhouse and even hothouse conditions, with global average temperatures around 6 to 9°C warmer than the present ones. There are only sparse and controversial evidence for polar ice; meanwhile, extensive evaporitic and desertic deposits are well described. Global sea levels were mainly high, and the content of atmospheric O2 was varying between 15 and 25%. These conditions make the Mesozoic Earth an alien world compared to present-day conditions. Degassing from volcanism linked to the rifting process of Pangaea and methane emissions from reptilian biotas were climate-controlling factors because they enhanced atmospheric CO2 concentrations up to 16 times compared to present-day levels. The continental break-up modified paleopositions and shoreline configurations of the landmasses, generating huge epicontinental seas and altering profoundly the oceanic circulation. The Mesozoic was also a time of important impact events as probable triggers for “impact winters”; and for the Era at least nine huge (diameter > 20km) impact structures are known. This paper presents an abridged but updated overview of the Mesozoic paleogeographic and paleoclimatic variations, characterizing each period and sub-period in terms of paleoclimatic state and main tectonic and climatic events, and provides a brief geologic, stratigraphic, paleoclimatic and taphonomic characterization of dinosaur occurrences as recorded in the Brazilian continental basins.
The Tookoonooka crater in south-central Queensland, about 55 km in diameter, was discovered as anomalous circular structure in the early 1980s due to petroleum exploration when seismic profiles showed as a circular structure consisting of a concentric arrangement of anticlines and synclines, which surround a complex central dome, approximately 22 km wide.
The stable nature of Australian cratons allowed preservation of a comprehensive record of exposed and buried impact structures, including the classic 580 Ma Acraman-Bunyeoo impact and attended Acritarchs radiation and a number of large buried impact structures and probable impact structures, including Woodleigh, Gnargoo, Tookoonooka, Talundilly, Mount Ashmore and Warburton, identified by geophysical methods and drilling.
The Tookoonooka impact structure is a subsurface structure of the Eromanga Basin in Australia. Impact ejecta have recently been discovered in the stratigraphy proximal to the structure. The ejecta includes accretionary and armored impactoclasts. They are observed at multiple locations in drill core across central Australia, spanning 375,000 km2 within possible impact tsunami deposits. Typical characteristics of the accretionary impactoclasts include a distinctive brownish-gray color, flattened shapes, concentric zonation, and a variety of morphologies with and without obvious nuclei. Some complex accretionary impactoclasts include melt components. Apparent diameters of these impactoclasts in drill core are commonly less than 2 cm, but may be up to 9 cm. They occur in a variety of depositional contexts, including clast-supported breccia-conglomerate layers and "floating" within massive and planar-bedded sandstones. Microscopic and geochemical investigations reveal that they are pervasively altered. Many resemble the types of accretionary lapilli recognized from hydroclastic volcanic environments, which implies the presence of significant water at the time of impact. Tookoonooka is interpreted to have been a marine (likely paralic to shallow) impact event. It is proposed that hydroclastic types of accretionary impactoclasts at impact sites may be an indicator of wet or marine targets. Complex forms of accretionary impactoclasts may also lead to new understanding of impact vapor plume processes. The impactoclasts studied at Tookoonooka are consistent with an impact origin of the candidate ejecta. The consistent first occurrence of the impactoclasts at the base of the Wyandra Sandstone Member stratigraphically constrains the Tookoonooka impact age to 125 ± 1 Ma in the Lower Cretaceous.
The discovery of large asteroid impact structures, likely and possible impact structures, onshore and offshore the Australian continent (Woodleigh [120 km; similar to 360 Ma], Gnargoo [75 km; Lower Permian - upper Cretaceous], Tookoonooka [55-65 km; similar to 125 Ma], Talundilly [similar to 84 km; similar to 125 Ma], Mount Ashmore [>100 km; end-Eocene] and Warburton twin structures [>400km; pre-end Carboniferous]) requires re-examination of the diagnostic criteria used for their identification. Bouguer anomalies of established impact structures (Chicxulub [170 km; 64.98 +/- 0.05 Ma], Woodleigh impact structure and Gnargoo probable impact structure display a unique structural architecture where pre-impact structural ridges are intersected and truncated by the outer ring of the circular structure. Seismic reflection data outline circular central uplift domes, basement plugs and rim synclines. Sharp circular seismic tomography anomalies indicate low velocity columns under both the Woodleigh impact structure and Warburton probable impact, hinting at deep crustal fracturing. Deformed, curved and clouded intra-crystalline planar deformation features in quartz (Qz/PDFs), displaying Miller indices ({10-11}, {10-12}, {10-13}) diagnostic of shock metamorphism, abound around exposed established impact structures (Vredefort [298 km; 2023 +/- 4 Ma], Sudbury [similar to 250 km; 1850 +/- 3 Ma], Charlevoix [54 km; 342 +/- 15 Ma], Manicouagan [100 km; 214 +/- 1 Ma]), Tookoonooka and Talundilly). Deformed Qz/PDFs allow recognition of shock metamorphism in buried impact structures, where original Qz/PDFs were bent, recrystallized and/or clouded during formation of the central uplift and hydrothermal activity triggered by the impact. Planar deformation in quartz can also occur in explosive pyroclastic units but are limited to Boehm lamella (Brazil twins) with single lamella sets {0001}. It has been suggested that a class of microstructures in quartz, referred to as metamorphic deformation lamella (Qz/MDL), occur in endogenic tectonic-metamorphic terrains. However, no type locality has been established for Qz/MDL of non-impact origin.
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