Woodleigh crater

Woodleigh is a large meteorite crater in Western Australia, centered on Woodleigh Station east of Shark Bay. A team of four scientists at the Geological Survey of Western Australia and the Australian National University, led by Arthur J. Mory, announced the discovery in the April 15, 2000 issue of "Earth and Planetary Science Letters" cite journal | author=Mory AJ, Iasky RP, Glikson AY, Pirajno F | title=Woodleigh, Carnarvon Basin, Western Australia: a new 120 km diameter impact structure | journal=Earth and Planetary Science Letters | volume=117 | issue= | year=2000 | pages=119–128 | id= | doi=10.1016/S0012-821X(00)00031-5 [http://dx.doi.org/10.1016/S0012-821X(00)00031-5 Abstract] ] .

The crater is not exposed at the surface and therefore its size is uncertain. The original discovery team believe it may be up to 120 kilometres in diameter , but others argue it may be much smaller, with one study suggesting a diameter closer to 60 kilometres cite journal | author=Reimold WU, Koeberl C, Hough RM, Mcdonald I, Bevan A, Amare K, French BM | title=Woodleigh impact structure, Australia: Shock petrography and geochemical studies | journal=Meteoritics & Planetary Science | volume=38 | issue= | year=2003 | pages=1109–1130 | id= [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003M%26PS...38.1109R&db_key=AST&data_type=HTML&format=&high=44810356c609136 Abstract and full PDF] ] . The larger estimate, if correct, would make this the fourth largest confirmed impact structure in the world, and imply a bolide (asteroid or comet) about 5–6 kilometres in diameter cite journal | author=Mory A, Iasky R | title=Woodleigh — Australia’s largest impact structure? | journal=Fieldnotes, Geological Survey of Western Australia, ISBN 0-7307-5642-4 | volume=16 | issue= | year=2000 | pages=1–2 | id= [http://www.google.com/url?sa=t&ct=res&cd=4&url=http%3A%2F%2Fwww.doir.wa.gov.au%2Fdocuments%2Fgswa%2Fgsd_fld_woodleigh.pdf&ei=t4JwRICaKonSaJm91LkG&sig2=0pIONWgQvDMyTryKQDYT4Q PDF] ] . The central uplift, interpreted to be 20 kilometres in diameter, was first intersected by drilling activities in the late 1970s; however its significance as an impact structure was only realised in 1997 during a gravity survey . In 1999 a new core sample was taken. The thin veins of melted glass, breccia, and shocked quartz found would have formed under pressures 100,000 times greater than atmospheric pressure at sea level, or between 10 and 100 times greater than those generated by volcanic or earthquake activity. Only a large impact could have generated such conditions.

The Woodleigh impact event, originally thought to have occurred between the Late Triassic and Late Permian, is now thought to date from 364 ± 8 million years (Late Devonian) cite web | title=Woodleigh | work=Earth Impact Database | url=http://www.unb.ca/passc/ImpactDatabase/images/woodleigh.htm | accessdate=2007-02-10 ] . This time corresponds approximately to a minor extinction event when around 40% of species disappeared. There is evidence for other large impact events at around the same time, so if the extinction is related to impact, perhaps more than one crater was involved.

Of the two dozen or more impact craters known in Australia, the three largest are Woodleigh, Acraman, and Tookoonooka .

The vicinity to Shark Bay and its orientation suggest the bay is the incipient part of the hotspot track of the Woodleigh impact.Fact|date=September 2008 Most of the track, which is cut off at the edge of the continental shelf, would be lost after the break-up of Gondwana.

References

External links

* [http://www.doir.wa.gov.au/GSWA/594A90F2EB2643BCA0B9D5EB66505AEC.asp WA Geological Survey Meteorite Impacts in Western Australia]