Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia
Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia
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Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia
Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia
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The cause of the catastrophic mass extinction at the end of the Permian has been the focus of considerable debate. Becker et al., (1-3) and others (4-10) have presented evidence that a major impact was associated with the extinction of > 90% of marine taxa. The evidence includes fullerenes with extraterrestrial helium and argon (1,7), meteorite fragments (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).

Acceptance that an impact accompanied the K/T extinction increased dramatically with the discovery of the Chicxulub crater (11,12). We searched for a Permian-Triassic (P/Tr) boundary impact crater in the southern hemisphere that once comprised the supercontinent of Gondwana because the impact evidence is most abundant in continents from this region (e.g. Australia, Antarctica). Gorter, based on the study of a single seismic line (13,14), suggested that the Bedout (“Bedoo”) High offshore of Northwestern Australia might be the central uplift of a large end-Permian impact crater. In this paper, we describe the Bedout structure and present evidence from drill cores, additional seismic and gravity data and Ar/Ar dating of plagioclases that Bedout is a large buried end-Permian impact crater and possibly the source of the P/Tr ejecta deposits distributed globally (Fig. 1, S-1 below).
Figure 1 - Positions of the continents during end-permian time. Red clots denote where extraterrestrial fullerenes have been reported (1-3). In addition, several other impact tracers have been found in the Permian-Triassic boundary layers at Graphite Peak, Meishan, China and Sasayama, Japan including meteoritic debris (8), Fe-Ni-Si grains (5,8), shocked quartz (4), impact spherules (6). Recently, large quartz grains (S-1) were found in the Fraser Park, Australia (yellow dot) and Graphite Peak, Antarctica, Permian-Triassic boundary layers. (Permian map modified from Scotese Paleomap Project website: www.scotese.com) Click here for larger view)

S-1 Large shocked quartz grains with planar deformation features (PDFs) identified in the Fraser Park, Sydney Basin Permian-Triassic boundary layer. Inset in upper photo shows close-up of intersecting PDFs. Quartz grains are mounted in oil and photographed in plane polarized light. Click here for larger view)

Geology of the Bedout Structure
The Bedout High is part of the Roebuck basin that forms the northwestern continental margin of Australia (Fig. 2 below).


Figure 2. Base map of the offshore northwestern Canning basin region showing the major tectonic elements (i.e. plateaus, basins, platforms, etc.), the Bedout High with the Lagrange-1 and Bedout-1 exploration wells located on top of the high (red dots) and two AGSO regional seismic reflection lines (see Figs. 10, S-15) and the JNOC (JN87-12;) seismic line (Fig. 3) that cross over the high (base map modified from 17).
Click here for larger view)

Existing studies of the structure include two regional seismic surveys conducted by the Australian Geological Survey (AGSO) and the Japan National Oil Company (JNOC) and two exploratory wells drilled 9 km apart on the top and flank of the Bedout High, Bedout-1 and Lagrange-1, that extend to depths of 3052 m (9986 ft.) and 3273 m (10,738 ft.), respectively (Fig. 3, S-2).

 

 

 

 

Figure 3. Interpreted section of the multichannel seismic line JN87-12 showing correlated ties to Bedout-1 and Lagrange-1 gamma (left) and sonic (right) well logs (modified from Smith, 1999, 15 ; location of line in Fig. 2). Color stratigraphic horizons represent chronostratigraphic picks (CT-1, early Jurassic, red; SQ-2, middle Triassic, blue; Unit VIII, late Permian, purple). The < >Triassic sediments overlying the late Permian (Unit VIII) are thin, however, all of the units (late, middle, early) were identified in the Bedout-1 and Lagrange-1 core and cuttings (S-2). Click here for larger view)

 

 

 

 

S-2. Stratigraphic columns of key wells in the Canning Basin region (after Smith et al, 1999; ref. 15).
Click here for larger view)

 
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Contents . 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11
Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia
Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia