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Silverpit crater is a buried sub-sea structure under the North Sea off the coast of the island of Great Britain. The crater-like form, named after the Silver Pit — a nearby sea-floor valley recognized by generations of fishermen — was discovered during the routine analysis of seismic data collected during exploration for gas in the Southern North Sea Sedimentary Basin. Its meteor impact origin was first proposed and widely reported in 2002.〔 〕 If correct, it would be the first impact crater identified in or near Great Britain. Its age was proposed to lie somewhere in a 29-million year interval between 74 – 45 million years (Late Cretaceous – Eocene).〔 〕 However, the interpretation is controversial and other authors have disputed its extraterrestrial origin. An alternative origin has been proposed in which the feature was created by withdrawal of rock support by salt mobility.〔 〕 ==Discovery== The crater-like structure was discovered by petroleum geoscientists Simon Stewart of BP and Philip Allen, then of Production Geoscience Ltd, during routine analysis of seismic data while exploring for natural gas deposits in a region 130 km off the Humber estuary. Allen noticed an unusual set of concentric rings. Although they looked as if they may have been caused by a meteor, he had no experience of impact structures. So he hung an image of them on the wall of his office, hoping someone else might be able to shed light on the mystery. Stewart, visiting Production Geoscience on an unrelated matter, had long predicted that a crater would be found on 3D seismic data, saw the image and suggested it might be an impact feature. The discovery of the crater and the impact hypothesis were reported in the journal ''Nature'' in 2002.〔 Silverpit crater is named after the Silver Pit fishing grounds in which it is located. The name is given by fishermen to a large elongated depression in the bed of the North Sea, which is thought to be an old river valley formed while the sea level was lower during the Ice Age. The structure currently lies below a layer of sediment up to 1,500 m thick, which forms the bed of the North Sea at a depth of about 40 m. Stewart and Allen's studies suggest that at the time of its formation, the area was under 50 to 300 m of water.〔 Only three years before the announcement of the discovery of the Silverpit crater, it had been suggested that seismic data from the North Sea would have a good chance of containing evidence of an impact crater: given the rate of crater formation on the Earth and the size of the North Sea, the expected number of impact craters would be one. Finding the crater form at Silverpit was serendipity.〔 〕 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「Silverpit crater」の詳細全文を読む スポンサード リンク
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