Bedout
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Bedout or Bedout High, (IPA pronunciation: [bedʉː]) is about 25 km off the northwestern coast of Australia in the Roebuck basin. It is a large circular depression in the ocean basin approximately 200 km across, with a central uplift that is a distinguishing feature of impact craters (see Chesapeake Bay impact crater for comparison). It was noted in 1996 by Australian geologist John Gorter of Agip in currently submerged continental crust off the northwestern shore of Australia. The geology of the area of continental shelf dates to the end of the Permian.
Some scientists speculate that Bedout might be the result of a large bolide impact event that occurred around 250 million years ago; a large impact event during that time frame, incurring other factors, could account for the Permian-Triassic extinction event . Geologist Luann Becker, of the University of California, found shocked quartz and brecciated mudstones and other mineralogical evidence of impact conditions at the site [1]. Several Permian-Triassic boundary sites have produced evidence of impact material prior to the Bedout discovery: shocked quartz from sites in Antarctica and Australia, glassy spherules at sites in China and Japan, fullerenes with evidence of extra-terrestrial gases in P-Tr sites in Japan and southern China (Becker et al, 2001). Another site (Wilkes Land crater in Antarctica) has also been proposed as the P-Tr impactor.
Sediment samples appear to match the date of the extinction event. The Bedout impact crater is also associated in time with extreme volcanism and the break-up of Pangea. "We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Dr. Becker explains. "This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don't think we can call such catastrophes occurring together a coincidence anymore," Dr. Becker added in a news release [2].
Significant erosion has affected the structure, and differences in subsidence have tilted it. Skeptics contend that the shape of the depression is inconsistent with bolide impacts; instead, the depression might be explained by other scenarios, such as an oddity in the earth's structure. In addition, iridium anomalies, a feature associated with other massive bolide impacts, have not been found. Continuing research could yield more clues in the years to come.
See List of impact craters on Earth.
