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Burckle Crater is an undersea feature hypothesized to be an impact crater by the Holocene Impact Working Group. They considered that it likely was formed by a very-large-scale and relatively recent (c. 3000–2800 BC) comet or meteorite impact event. It is estimated to be about 30 km (18 mi) in diameter,〔Martos, S.N., H.D. Elkinton, E.F. Bryant, V. Gusiakov, and D. Breger (2006) (''Impact craters as sources of megatsunami generated chevron dunes.'' ) Geological Society of America Abstracts with Programs. 38(7):299〕 hence about 25 times larger than Arizona's Meteor Crater. It is east of Madagascar and west of Western Australia in the southern Indian ocean adjacent to the SW Indian Ocean Ridge.〔 Its position was determined in 2006 by the same group using evidence of its existence from prehistoric chevron dune formations in Australia and Madagascar that allowed them to triangulate its location. But the theory that these chevron dunes are due to tsunamis has been challenged by geologists Jody Bourgeois and R. Weiss. Using a computer model to simulate a tsunami, they argue that the structures are more consistent with aeolian processes.〔Bourgeois, J., and R. Weiss (2009) ('' 'Chevrons' are not mega-tsunami deposits; a sedimentologic assessment.'' ) Geology. 37(5):403-406.〕 The tsunami's origin of these chevrons is also disputed by other Earth scientists.〔Pinter, N., and S.E. Ishman, S.E. (2008). ( ''Impacts, mega-tsunami, and other extraordinary claims.'' ) GSA Today. 18(1):37.〕 Burckle Crater is at in the Indian Ocean and is 12,500 feet (3,800 m) below the surface. ==Formation== Burckle Crater has not yet been dated by radiometric analysis of its sediments. The Holocene Impact Working Group think that it was created about 5,000 years ago (c. 2800–3000 BC) during the Holocene epoch when a comet impacted the ocean, and that enormous megatsunamis created the dune formations which later allowed the crater to be pin-pointed. Unusual calcite (CaCO3) crystals, translucent carbon spherules, fragments of basaltic glass and native metals (native iron and nickel) are reported near the crater and associated with impact ejecta or hot water precipitates. Seawater at the depth of the crater is undersaturated with respect to calcite and rapid burial would be needed to preserve those crystals.〔Abbott, D.H., P. Gerard-Little, S. Costa, and D. Breger (2009) (''Odd (CaCO3) from the Southwest Indian Ocean near Burckle Crater candidate; impact ejecta or hydrothermal precipitate?'' ) Abstracts of Papers Submitted to the Lunar and Planetary Science Conference. vol. 40, abstract 2243. Lunar and Planetary Science Conference : Houston, Texas.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Burckle Crater」の詳細全文を読む スポンサード リンク
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