Bedout , or more specifically the Bedout High, is a

geological Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...

and

geophysical Geophysics () is a subject of natural science concerned with the physical processes and properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct investigations acros ...

feature centered about off the northwestern coast of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

in the

Canning Canning is a method of food preservation in which food is processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although under ...

and overlying Roebuck basins. Although not obvious from sea floor topography, it is a roughly circular area about in diameter where older rocks have been uplifted as much as towards the surface and may mark the centre of a very large buried

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

up to in diameter.Gorter J.D. 1996. Speculation on the origin of the Bedout high - a large, circular structure of pre-Mesozoic age in the offshore Canning Basin, Western Australia. PESA News, October/November 1996, p. 32-34. The Bedout High was penetrated by two petroleum exploration wells (Bedout-1, Lagrange-1) in the 1970s and 1980s. It is named after nearby Bedout Island.

Impact hypothesis

In 1996 Australian

geologist A geologist is a scientist who studies the structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...

John Gorter first suggested that the Bedout High might mark the centre of a very large buried impact crater up to in diameter, based mainly on its internal geological structure as revealed on a single

seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

survey line, and suggested that it may be of near end

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

age, based on the reported age of volcanic rocks in Lagrange-1.Gorter J.D. 1998. The petroleum potential of Australian Phanerozoic impact structures. The APPEA Journal 38, 159-187. The impact hypothesis was developed further by Luanne Becker (

University of California The University of California (UC) is a public university, public Land-grant university, land-grant research university, research university system in the U.S. state of California. Headquartered in Oakland, California, Oakland, the system is co ...

) and coworkers who claimed to have confirmed that the supposed volcanic rocks in the petroleum wells are actually impact melt

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

showing evidence of

shock metamorphism Shock metamorphism or impact metamorphism describes the effects of shock-wave related deformation and heating during impact events. The formation of similar features during explosive volcanism is generally discounted due to the lack of metamorp ...

, and re-dated these rocks at 250.1 ± 4.5 Ma.Becker L., Poreda R.J., Basu A.R., Pope K.O., Harrison T.M., Nicholson C. & Iasky R. 2004. Bedout: A possible end-Permian impact crater offshore of northwestern Australia. Science 304, 1469-1476
Abstract
/ref> The new age is essentially coincident with the

–

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

boundary and associated

extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...

, and Becker speculates that there is a likely connection. It was subsequently reported, based on very limited preliminary data, that the impact hypothesis is further supported by

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

evidence for the presence of extraterrestrial material.Becker L., Shukolyukov A., Macassic C., Lugmair G. & Poreda R. 2006. Extraterrestrial Chromium at the Graphite Peak P/Tr boundary and in the Bedout Impact Melt Breccia. Lunar and Planetary Science XXXVII (2006), abstract # 232
PDF
/ref>

Rebuttals to the impact hypothesis

The Bedout impact hypothesis has not been widely supported by impact cratering specialists. Specific counter claims include: # The alleged impact melt breccia actually has the characteristics of a volcanic

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

, in part altered by contact with sea water and

metamorphism Metamorphism is the transformation of existing Rock (geology), rock (the protolith) to rock with a different mineral composition or Texture (geology), texture. Metamorphism takes place at temperatures in excess of , and often also at elevated ...

due to its deep burial, and the evidence for shock metamorphism is likely mistaken.Glikson A. 2004. Comment on ‘‘Bedout: A possible end-Permian impact crater offshore of northwestern Australia’’. Science 306, 613
PDF
/ref>Glikson A. 2004. Bedout basement rise, offshore northwestern Australia: evidence of an unshocked mafic volcanic hyaloclastite volcanic breccia. Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract B33C-0269
Abstract
# A crater of the purported size would have produced a widespread layer of ejecta, but no such eject is evident at the nearest Permian-Triassic boundary sites in Australia.Wignall P., Thomas B., Willink R., Watling J., Becker L., Poreda R.J. & Pope K.O. 2004. Is Bedout an impact crater? Take 1. Science 306, 609-610. # The presented evidence for impact fails to meet established standards, and the dating methodology is flawed.Renne P.R., Melosh H.J., Farley K.A., Reimold W.U., Koeberl C., Rampino M.R., Kelley S.P., Ivanov B.A., Becker L., Poreda R.J., Basu A.R., Pope K.O., Harrison T.M., Nicholson C. & Iasky R. 2004. Is Bedout an impact crater? Take 2. Science 306, 610-612. # A detailed re-evaluation of the geophysical data indicates that the evidence is not consistent with the expected properties of a giant impact crater, but rather the Bedout High was likely the result of episodes of continental rifting.Müller R.D., Goncharov A. & Kristi A. 2005. Geophysical evaluation of the enigmatic Bedout basement high, offshore northwest Australia. Earth and Planetary Science Letters 237, 265-284.

References

External links

Stephen Earle, "Double jeopardy at the end of the Permian - new evidence for a large impact"
{{Webarchive, url=https://web.archive.org/web/20160303231658/http://records.viu.ca/~earles/bedout-jun04.htm , date=2016-03-03 Possible impact craters on Earth Impact craters of Western Australia Permian impact craters Triassic impact craters Permian Australia Triassic Australia Geography of the Indian Ocean Permian–Triassic extinction event

Impact hypothesis

Rebuttals to the impact hypothesis

See also

References

External links