Australia: The Land Where Time Began

A biography of the Australian continent 

Bedout High (Bedout Rise, Bedout Structure) see Marusek Hypothesis

Situated off the northwestern margin of the Australian continent, the Bedout High has been suggested to be an impact structure, and one that is being seen by some as a prime candidate for an end of Permian structure. Drill cores taken from the top of the structure have found melt rocks and impact breccias, and there are data from seismic and gravity studies, that are consistent with the presence of a buried impact crater. Silica glass, S_IO₂, that was almost pure, and plagioclases that were fractured and shock-melted, and spherulitic glass, have been found in the breccia. The presence of a melt sheet is indicated by the distribution over hundreds of metres of drill core of glass and shocked minerals. The Bedout High is suggested by the available gravity and seismic data to be the central uplift of a crater of similar size to that of Chicxulub. An Ar/Ar age of 250.1 ± 4.5 Ma has been determined for plagioclases separated from the Lagrange-1 exploration well. In Permian-Triassic boundary sediments worldwide, the reported presence of impact debris can be accounted for by the location, size and age of the Bedout Crater (Becker et al., Source 1).

There has been considerable debate concerning catastrophic mass extinction at the close of the Permian. Evidence has been presented by Becker et al. (1-3) and others (4-10) that a major impact was associated with the extinction event that killed off more than 90 % of marine taxa. Included in this evidence are fullerenes with extraterrestrial helium and argon (1,7), fragments of meteorite (8), Fe-Ni-Si “metamorphosed grains” of probable meteoritic origin (5,8,9) Fe-Ni metals with impact spherules (6,10) and shocked quartz (4).

When the Chicxulub Crater was discovered that occurred at the Cretaceous-Tertiary (K-T) boundary at the time of the mass extinction event acceptance of the idea that an impact accompanied the extinction event increased dramatically (11,12). Becker’s team searched for a crater at the boundary on the Permian-Triassic (P-T) in parts of the Southern Hemisphere that had once been part of the supercontinent of Gondwana, as the evidence of impact was found to be most abundant in continents in this region, such as Australia and Antarctica. Based on the study of a single seismic line (13,14),  Gorter suggested that the Bedout (“Bedoo”) High off the coast of northwestern Australia might be the central uplift of a large crater dating to the end of the Permian. In this paper Becker et al. describe the Bedout structure and present evidence from drill cores, as well as seismic and gravity data, and Ar/Ar dating of plagioclases that Bedout is an impact crater that is large, buried, and occurred at the end of the Permian, that is possibly the source of the P-T ejecta deposits that are distributed globally.

Geology of the Bedout structure

The Bedout High is part of the Roebuck Basin which forms the continental margin of the Australian continent. Included among existing studies are 2 regional seismic surveys that were conducted by the Australian Geological Survey (AGSO) and the japan National Oil Company (JNOC) (15) and 2 exploratory wells that were drilled 9 km apart on the top and the flank of the Bedout High (Bedout-1 and Lagrange-1) that extend to depths of 3,250 m (9,986 ft) and 3,273 m (10,738 ft), respectively. These wells were both drilled through about 3 km of marine and fluvial sediments that consisted of carbonates and occasional interbeddefd siltstones and mudstones, dating from the Tertiary to the Cretaceous, with sandstones that were interbedded with claystones, siltstones and coal, Tertiary to Triassic, after which a breccia was encountered from the Late Permian (16). The Bedout High was crossed by 2 of the 14 AGSO regional seismic lines. Also, 4 wells penetrated Permian strata offshore that aid in defining the Bedout structure and stratigraphy. In the Lagrange-1 and the Bedout-1 cores and cuttings, Fluviatile and marine Keraudren sediments dating to the Middle to Late Triassic, were deposited directly on top of the breccia of Late Permian age.

At the present the Bedout High rises to several kilometres above the surrounding basement (17). It is also suggested by deep crustal reflections and seismic refraction velocities that the Bedout High is underpinned by elevated middle and lower crust. Core and cuttings, that were catalogued as basalts and referred to as a “volcanic breccia”, were both recovered from the top of the top of the High. This regional “volcanism” that was associated with the rifting of the Australian continental margin has been classified as the “Bedout Movement” of P-T age (18,19). There is a regional angular unconformity at the top of the High, which is consistent with uplift and erosion at the end of the Permian, immediately after the formation of the Bedout High and termination of the Bedout Movement (20). The rifting of the continental “Sibumasu Sliver” off northwestern Gondwana was coincident with the formation of the Bedout High (21). The post-impact tectonism, uplift, faulting and erosion during the Triassic and Jurassic that resulted overprinted regionally the Bedout structure and deformed the original complex morphology of the crater.

The Bedout Breccia

Lagrange-1 and Bedout-1 exploration wells both ended in what was inferred to be volcanic breccia. 52 m - 30 m of cuttings and 22 m of core – were recovered from the breccia unit in Bedout-1, and 391 m of cuttings were sampled from the breccia unit in Bedout-1, and 391 m of cuttings were sampled from the breccia unit in the Lagrange-1 drill hole. A series of centimetre-sized clasts are displayed by the Bedout core, some of which had variable banding and others that are poorly sorted, with chaotic dips of 30^o to 50^o in hand specimens, over the entire length of the core (20).

Throughout the core most of the clasts are dark green and massive, appearing glassy in hand specimens, though in thin section many are seen to be partially altered to fine grained chlorite or a mixture of fine grained plagioclase, carbonate, and iron oxides. From the lowest section of the core, at 3,044 m (9,986 ft), Becker et al. identified unaltered glass and relic igneous mineral grains. Also, large, highly fractured plagioclase phenocrysts were present in a section from higher in the core at 3,041 m (9,977 ft). Many small rock and mineral clasts in predominantly glassy matrix that had been partially altered to chlorite are present in the basal 8 m of the core. Evidence of flow structures is shown in brownish glass, and calcite was observed as veins and cavities in several thin sections. The mineral clasts are comprised of mostly single and multiple aggregates of plagioclase, and the clasts are of glassy fragments. In the lower 8 m of the core the complex mixtures are of very different textures that are similar to the cores from inside the Chicxulub crater (22-25).

Shocked minerals surrounded by a matrix consisting almost entirely of glass, with the exception that it has been altered to chlorite, are contained in the clasts from 3,344 m (9,986 ft). Included in the samples are shock-melted plagioclase that has been completely or partially converted to glass, spherulitic glass, and pure silica glass. Diaplectic glass (maskelynite), that has a composition that is identical to that of the surrounding plagioclase anorthosite (An₅₀), is enclosed in plagioclase. Becker et al. also identified grains that are stoichiometrically ilmenite, heterogeneous silica glass, albite, sanidine, and a carbonate (CaCO₃) clast that is partially melted with fragmented ooids (26,27). Sanidine, which was identified optically and confirmed by microprobe analysis of a 10-μm grain, has 43 % albite in solid solution with no sign of segregation (microperthite).

The Lagrange-1 cuttings consist of various types of partially crystalline and partly glassy rock that has a mostly basaltic composition. Some of the fragments are identical to those present in the Bedout core. At 3,255 m (10,679 ft) one of these fragments shows feldspar crystallites (laths) in “swallowtail” terminations, which indicates rapid crystallisation from the glassy matrix. Heterogeneous compositions are displayed by the feldspar laths, and they are mixtures of either pure albite or K-feldspar in their glassy matrix, as seen in the backscattered image of one of the grains. These textures, chemistry, mineralogy, and mixture of different fragments were interpreted by Backer et al. as indicating that the basal 8 m of Bedout-1 is an impact melt breccia.

The plagioclase crystals that are completely or partially melted and fractured and abundant glassy clasts are most diagnostic. The coexistence of silica glass rich in titanium is in close proximity (within 1 mm) to silica glass that is slightly aluminous but poor in titanium requires silicate liquid immiscibility that has not been seen in terrestrial magmatic environments.

Features that are attributable to a melt that is generated by impact include carbonate lithic fragments that have been partially melted and recrystallised and spherulitic glasses, which were partially altered to chlorite, that has a different chemical composition from the glassy matrix. Magnesian-ilmenite is found as microlites in the matrix is also a mineral that is not commonly present in volcanic rocks. According to Becker et al. the glassy rock clasts can be attributed to the melting of target materials containing sediments rich in magnesium, such as dolomites, and common Fe-Ti oxides, such as magnetite, titanite “sphene,” and rutile, which are found in crustal environments. Overall, the compositions of the minerals and glasses of the Bedout core are consistent with a heterolithic impact breccia, or suevite, that is melt rich, that is formed by the heterogeneous melt formation and subsequent quenching and crystallisation that is triggered by impact. Such compositions are not known and are not likely to exist in terrestrial volcanic agglomerates, lava flows and intrusive pipes. Individually, these minerals may occur only rarely in volcanic or plutonic rocks, though never in association with each other.

Natural volcanic processes, in particular, generate silicate melts up to, though not exceeding, about 78 %. When taken as a whole these features are most consistent with melting that is generated by impact. Volcanism that is not associated with rifting does not produce melts (glasses), nor does any other endogenous magmatic process. Overall, the textures of these heterolithic fragments, especially the Bedout glasses, are similar to the features of the Sudbury Onaping breccia and the melt breccia that is found in the Chicxulub crater.

Ar/Ar dating of the Bedout core

⁴⁰Ar/³⁹Ar dating was undertaken by Becker et al. of the feldspar concentrates from the Bedout-1 core and Lagrange-1 impact breccia by step-heating and single crystal fusion experiments. It is indicated by ⁴⁰Ar/³⁹Ar dates on 6 individual plagioclases from 3,041 m (9,977 ft) obtained from the Bedout-1 core that the ages are much younger than the overlying Triassic sediments. Significant alteration in plagioclase grains and possibly K addition are revealed by petrographic and microprobe examination of the Bedout core from 3,044 (9,986 ft) and 3,041 m (9,977 ft.). Individual grains of feldspar display Heterogeneous chemical compositions resulting from alteration or disequilibrium in the sample cuttings. The glassy matrix at 3,044 m (9,986 ft.) has potassium concentrations that are extremely low, <0.1 %, and proved to be unsuitable for ⁴⁰Ar/³⁹Ar dating. A plagioclase at 3,255 m (10,679 ft.) from the Lagrange-1 cuttings, which displayed the least alteration or disequilibrium, has an ⁴⁰Ag/39Ar age of 250.2 Ma, that has a plateau portion between 8 and 90 % gas release at 250.1 ± 1 , consistent with the previous K-Ar measurements on the plagioclase separate from Lagrange-1 (253 ± 5 Ma). In the Yacatan-6 melt rocks from the Chicxulub crater similar problems in dating plagioclase separates were encountered (23).

Geophysical Evidence

Becker et al. reinterpreted some seismic lines that had been provided by AGSO (18) that had originally been interpreted by Gorter (13,14) when it was confirmed that the Bedout High consists of an impact breccia and melt sheet. For line S120-01 the revised chronostratigraphy includes the Lagrange -1 and Bedout-1 stratigraphic sections, which correlated with adjacent onshore seismic sections and wells (31), and the Ar-Ar and K-Ar dating on the melt breccia. The top of the Permian is conformable with the Bedout High, while the sediments from the Triassic unconformably onlap onto the structure. A broad uplifted core of basement 40-60 km in diameter elevated to a minimum of 6 to 9 km is displayed by the revised seismic section. Inferred only from the seismic character correlations (16) the “pre-Permian” strata are not imaged well in the seismic data, yet they appear to show uplift with the basement core. As the deeper material has not yet been sampled and dated, these sequences could alternatively all be crater fill impact debris from the end-Permian. A slight uplift of Permian and earlier strata was also detected by Becker et al. at a radius of about 100 km from the centre of the Bedout High, though it is not clear that this is a concentric feature. A central uplift is revealed beneath the Bedout High, with about 6-7 km of vertical structure relief on midcrustal isovelocities, was derived from ocean bottom seismometer wide angle reflection and refraction data that had been collected along the S120-01 line (32). The data, though less well resolved, also suggest possible variations in Moho depth beneath the Bedout High (33). However, it is difficult to assess if this Moho topography , as in the case of the Chicxulub crater, results from the dynamic effects of the crater- (and Bedout High-) forming process extending down to the base of the crust (33-35) or is the result of later rifting of the continental margin.

In the Early to Middle Triassic the Bedout structure was emergent and is probably deeply eroded. In the Canning Basin, onshore much of the section dating to the Permian and Early Triassic is missing: over 0.5 to 1.0 km of section overall, and on topographic highs as much as 2 km (36). The depth of erosion at Bedout is known, though it is probable that the unconformity at the top of the Permian represents a section that is missing. The Lagrange-1 well passes through several hundred metres of the impact melt breccia, though it is not certain how much more of the High is actual impact melt breccia. It is shown by both the isostatic residual gravity model for the Bedout structure and the Bouguer gravity over Chicxulub that a semicircular gravity low surrounding the expression for the central peak. The resolution of the offshore gravity data is unfortunately not of sufficient quality to obtain a vertical derivative image, which generally is used to highlight the gradient that are more subtle, as well as assessing the geomorphometric parameters, including size, of the Bedout structure. The diameter of the outer edge of the gravity low is about 100 km, and is of similar size to the Chicxulub gravity low that is better resolved.

Comparison of the Bedout structure with other impact structures

As was noted first by Gorter (13,14), the geophysical expression of the Bedout High shows similarities to the central uplift in other large impact craters. A characteristic negative gravity anomaly that surrounds a gravity high, is a feature that led to the initial discovery of Chicxulub (12), is produced by fracturing and brecciation that resulted from the impact of large meteorites with the crust. At Bedout there is just such an anomaly, though it is obscured somewhat by other features of the crust that are derived from younger tectonic overprinting, dating the Triassic and Jurassic. In the centre of large terrestrial craters the gravity high is due to the central uplift elevating basement rocks that are denser. The gravity high is associated with a structural high at Bedout. At Chicxulub the central uplift is seismically poorly imaged, and consists mostly of about 6 to 7 km of uplift of midcrustal isovelocities, and has a diameter of about 40 km to 60 km (33). According to Becker et al. these dimensions are well within the Bedout High, which suggests that Bedout may be about the same size as Chicxulub, about 200 m in diameter. The slight uplift that was noted at a radius of about 100 km at Bedout may be a subtle expression if the outer rim, though this is speculative. If the Bedout High is a central uplift similar to the central uplift at Chicxulub, then at Bedout the erosion could be extensive. As the top of the central uplift at Chicxulub lies about 3.5 km below the floor of the crater then erosion could be extensive at Bedout (37).

Across Bedout the seismic profile is similar to one across the Mjølnir Crater in the Barents Sea (38), with the exception that the central uplift of Mjølnir Crater is much smaller at 1.5-1.2 km high and 8 km wide. The central uplift of the Mjølnir Crater extends well above the pre-impact surface and appears to be the result of differential subsidence in the annular trough that surrounds the peak under the load of pre-impact sediments (39). At Bedout strata dating to the Permian are overlain by about 3-5 km of sediment, therefore it is possible that the relief of the Bedout High has been altered by differential subsidence since its initial formation.

Evidence for an impact in Gondwana at the P-T boundary

At Bedout High a large impact crater is consistent with the global distribution of impact ejecta at the P-T boundary and helps to explain apparent anomalies in the global patterns. Large impact ejecta fragments (>200 μm) have to date been found only in the P-T boundary sites that are relatively close to Bedout. Meteorite fragments that were recovered from the P-T boundary at Graphite Peak in Antarctica are in a size range from 50 to 400 μm. Becker et al. found shocked quartz that ranged in size from 150 to 550 μm at Frazer Park, which is adjacent to the well-known site at Wybung Head in the Sydney Basin (4) and grains up to 250 μm at Graphite Peak in Antarctica. At Frazer Park and Graphite Peak the shocked quartz comprises about 1 % of the quartz fraction, compared to about 50 % at many K-T boundary sites (40). It was suggested (Retallack et al., 1998) that such a small amount of shocked quartz at the P-T boundary may impact a minor impact, though Becker et al. interpret the low percentage as a product of dilution by reworking of the ejecta in an environment of continental deposition. In the Sydney Basin and at Graphite Peak the P-T boundary layer is a claystone breccia 10-20 cm thick that contains abundant rep-up clasts from the underlying soil (4), whereas the distal K-T boundary deposits that are rich in shocked quartz are composed mostly of ejecta and are less than 1 cm thick (41).

The maximum grain sizes of the shocked quartz from Frazer Park and Graphite Peak match well with the maximum sizes of the shocked quartz at the K-T boundary and their distance from Chicxulub when the maximum grain sizes of shocked quartz from Frazer Park and Graphite peak are plotted with respect to the distance from Bedout. It has been demonstrated by Pope (42) that the global distribution of shocked quartz at the K-T boundary is explained best by dispersal by winds in the stratosphere and the settling of the particles through the atmosphere. Becker et al. suggest that this type of mechanism is not efficient in latitudinal transport of debris and, therefore, shocked quartz from the impact at Bedout would be dispersed mostly over the Southern Hemisphere. This would indicate that a large impact at Bedout is consistent with the size of the shocked quartz that have been found in Australia and Antarctica as well as possibly explaining why such grains are not found further to the north.

Elsewhere, Meishan in China and Sasayama in Japan, metal nuggets of Fe-Ni-Si, oxides, and spherules ⁓30 to 200 μm in size are found at the P-T boundary (5,6,8,43). Spherules with refractory grains (Mg-Ni-Fe oxides and Si-Ca-Al oxides) of similar size from the K-T boundary have been attributed to formation in the vapour plume at Chicxulub (44), and a similar vapour plume origin has been proposed for the P-T spherules (5,8). These products of high energy vapour plume condensates in China and Japan without shocked quartz is consistent with an impact at Bedout. According to Becker et al. the apparent absence of P-T impact ejecta from sites far to the north of Gondwana, in the Laurasia supercontinent, that is now North America, Europe and most of Asia, may also be a consequence of an impact at Bedout in the far Southern Hemisphere, though more work is required to verify this hypothesis.

Discussion

Becker et al. presented evidence, geochemical, geochronological, biological and petrological, linking the Bedout structure to impact deposits to the end-Permian around the world. The difficulties involved in interpreting old impact structures that have subtle expressions and not retaining pristine characteristics of younger craters that are well-preserved such as Chicxulub, are emphasised in the recognition of an impact breccia in the Bedout High. Only the upper portion drill cores that were available were sampled (about 22 m of the intact core at Bedout-1and 391 m of cuttings at Lagrange-1, of the impact melt breccia and it was found that they contained impact melt breccia materials that were mostly highly shocked. According to Becker et al. the shock pressure that were indicated in the Bedout-1 core were sufficient to produce maskelynite (28), pressures of 35-45 GPa, and silica glass, >45-65 GPa. These pressures were too high to preserve planar deformation features in quartz, <35 GPa, though high enough to form stishovite, 15-40 GPa, and possibly hexagonal diamond, 70-140 GPa (45). Therefore other samples from Bedout High may produce additional evidence of shock, stishovite, coesite, and diamond, if it is assumed that suitable target rocks were present. Analyses in the future similarly may isolate pristine mineral grains that could be used for radiometric dating and therefore constrain better the age of the end-Permian and its association with the P-T boundary that has been hypothesised. Additional geophysical data, and possibly coring, are needed to better determine the size of the structure.

The evidence of yet another impact event (within the age uncertainty) with severe flood basalt volcanism raises the question of the relation of such catastrophes to each other as well as to mass extinctions (46) [see Marusek Hypothesis] (MHM). According to Becker et al. there has been increasing speculation that the impacts of large bolides have been responsible for processes such as continental flood basalt eruptions and mantle plumes (47,48). It is suggested by present models that if a volcanic outburst may be induced if a bolide strikes a pre-existing hotspot. The probability of such an event occurring is, however, extremely remote (49,50). In the case of Chicxulub, and now the Bedout High, the locations of the craters are opposite, instead of exactly antipodal to, the location of the volcanic province, the Deccan Traps in the case of Chicxulub and in the case of Bedout, the Siberian Traps. Melosh has calculated the amount of kinetic energy needed to create the volume of the Deccan Traps, about 500,000 km³, requires about 5 x 10²³ J, or twice the amount of kinetic energy that was generated by the Chicxulub impactor, 10 km at 20 km/s.

Becker et al. suggest that it seems clear that an impact may not be the direct cause of the volume of flood basalts; it may still act as a “trigger” for the event. Ar-Ar dating at both Siberia and Deccan has shown that volcanic rocks that have mantle plume affinities predate the main pulse of the Deccan and Siberian trap (51,52). Therefore the impact(s) and the sudden release of energy might enhance the catastrophic eruption of a pre-existing mantle plume. In order to properly assess, identify and confirm extraterrestrial impact events and to understand further the impact processes and their relation to severe volcanism and mass extinction events in the geological record may require new models to be considered.

Evidence has been presented by Becker et al., geochemical, biological and petrological, that genetically links the Bedout Structure to the worldwide impact deposits of end-Permian age (Fig.1, Source 1). According to Becker et al. the Bedout High is an example of old impact structures that have not retained the normal characteristics of younger impact craters such as Chicxulub (Hildebrand et al., 1991), the Bedout High being suggested to be a possible impact structure by the recognition of impact breccia. Only the upper portion of the Bedout High has been sampled, there ~22 m of intact drill core from Bedout-1 and 391 m of cuttings from Lagrange-1of the impact melt breccia, most of the material having been highly shocked. The shock pressures of 35-45 GPa recorded in the core from Bedout were high enough to produce maskelynite (French, 1998), and >45-65 GPa, to produce silica glass. The pressures are too high to preserve PDFs in quartz (<35 GPa), though high enough to form stishovite (15-40 GPa) and possibly hexagonal diamond (70-140 GPa) (Stöffler, 1972).

Becker et al. suggest that the evidence from the Bedout High adds to the growing evidence for a link between impacts and flood basalt eruptions, based on the impact event being coincident, within the age uncertainty, with severe flood basalt volcanism. They also suggest that the question is raised of the relationship of such catastrophes with each other, as well as with mass extinction events (Richow et al., 2002). Speculation has been increasing that the impacts of large bolides have been responsible for processes such as eruptions of continental flood basalt and mantle plumes (Jones et al., 2002; Glickson, 1999).

Present models suggest that volcanic eruptions may be induced  by a pre-existing hot spot being struck by a bolide, though the probability of such an event is extremely remote (Melosh, 2000; Ivanov & Melosh, 2003). The craters at Chicxulub and Bedout, are opposite, not exactly antipodal (Fig.1, Source 1) to the volcanic provinces of Deccan and Siberia respectively. The amount of kinetic energy required to create the volume of the Deccan Traps has been calculated (Melosh, 2000), about 500,000 km³, about 5 x 10²³ J, twice the amount of the kinetic energy generated by the Chicxulub impactor (10 km at 20 km/s). Becker et al. suggest the impact may not be the direct cause for the volume of flood basalts; it may act as a trigger of the event. According to Becker et al. volcanic rocks with affinities to mantle plumes have been shown to predate the main pulse of flood basalt at both the Deccan Traps and Siberian Traps. This suggests that the catastrophic eruption of a pre-existing mantle plume might be enhanced by the impact(s).

Evidence of an impact dating to the Permian-Triassic boundary is most abundant in the Southern Hemisphere, in the continents that were part of Gondwana, such as Australia and Antarctica. This led Becker et al.  to concentrate their search for an impact crater in these continents. Gorter suggested that the Bedout ("Bedoo") High might be the central uplift of a large end-Permian impact crater, based on a single seismic line (Gorter, 1996; Gorter, 1998). The Bedout High is in the Roebuck Basin that forms the northwest margin of the Australia continent (Fig.2, Source 1). A number of studies have been carried out on the Bedout High. AGSO carried out 2 regional seismic surveys and the Japan Oil Company, the quality of the data from the Japan Oil Company surveys being from poor to moderate, the results were being reprocessed in an attempt to improve quality. On the top and flank of the Bedout High 2 exploratory wells, Bedout-1 and Lagrange 1, were drilled 9 km apart, extending to 3,052 m (9,986 ft) and 3,273 m (10,738 ft) respectively (Fig. 2 and fig. S2, Source 1). Both wells reached a breccia dating to the Late Permian (Smith, 1999, fig. S2), after passing through about 3 km of marine and fluvial sediments, comprising carbonates, with some interbedded siltstones and mudstones, that have been dated to the Cretaceous to Tertiary, as well as sandstones interbedded with claystones, siltstones and coal, Triassic to Cretaceous. The AGSO crossed the Bedout High with 2 of their 14 seismic lines (Source 1, Fig. 2). There were also 4 wells offshore helping to identify seismic reflectors defining the structure and stratigraphy of the Bedout High, which penetrated Permian strata, 2 of which are shown in Fig. 2 (Source 1). Fluviatile and marine Keraudren sediments, from the Middle to Late Triassic, in cores and cuttings from Lagrange-1 and Bedout-1, show sediments that were deposited directly on top of the breccia from the Late Permian (Source 1, Fig. 4, figs. S2 & S3).

The Bedout High reaches several kilometres above the surrounding basement at present (Purcell & Purcell, 1994). The Bedout High is suggested to be underpinned by elevated middle and lower crust by deep crustal reflections and seismic refraction velocities. The core and cuttings catalogued as basalts, which have been referred to as "volcanic breccia", are from the top of the High. The "Bedout Movement" from the P/Tr boundary, is the regional volcanism associated with rifting of the Australian continental margin (Purcell & Purcell, Eds., 1994). At the top of the High there is a regional angular unconformity, which is consistent with uplift and erosion at the end-Permian, which is immediately after the Bedout High formation and termination of the Bedout Movement (Well reports Lagrange-1 & Bedout-1, 1971, 1983). The continental "Sibumasu Sliver" rifted off northeastern Gondwana, coincident with the formation of the Bedout High (Charlton, 2001). The complex crater morphology was deformed and the Bedout structure was overprinted by the tectonism, uplift, faulting and erosion that occurred in the Triassic and Jurassic as a result of the impact.

James Marusek proposed a mechanism that could link very large impacts with the Siberian Traps and Emeishan Traps, in China.

See Source 1 for more detailed information

Sources & Further reading

1.     Becker, L., R. J. Poreda, A. R. Basu, K. O. Pope, T. M. Harrison, C. Nicholson, and R. Iasky. "Bedout: A Possible End-Permian Impact Crater Offshore of Northwestern Australia." Science 304, no. 5676 (June 4, 2004 2004): 1469-76.

2.     Bedout: A Possible End-Permian Impact Crater Offshore of Northwestern Australia