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The Kentland crater, also known as the Kentland structure or the Kentland disturbed area, is an impact crater located near the town of Kentland in Newton County, Indiana, United States. It was discovered about 1880 when two farmers began to quarry crushed rock there. The presence of shatter cones and deformed bedrock led geologists to conclude by the late 1960s that the Kentland structure is an impact crater, rather than volcanic in origin. Deformation at the site is so great that vertical contacts between normally horizontal rock formations of different ages are common. The crater itself is a circular dome, about in diameter, deeply eroded and buried in glacial debris. Its age is estimated to be less than 97 million years (Cretaceous or younger). The Shakopee dolomite at the center of the structure is about 450 million years old (Ordovician period) and is uplifted about 2,000 feet higher than the level of the same rock in the surrounding area. The entire disturbed area is about in diameter. The estimated age is in dispute. * ‘’’97 MYA‘’’ Late Cretaceous Period of the Mesozoic Era 〔"Kentland". Earth Impact Database. University of New Brunswick. Retrieved 2009-08-17.〕 * ‘’’300 MYA‘’’= Bzhelian or Late Pennsylvanian Epoch(Carboniferous Period) of the Paleozoic Era〔Cochise College web-page, December 18, 2012〕 The crater's structure was studied in 1978. John Weber and his associates presented fission track dating of apatite from the crater.〔Society for Sedimentary Geology (SEPM) Research Conference, "The Sedimentary Record of Meteor Impacts" (21–23 May 2003, Springfield, Missouri)〕 Coesite and shatter cones are found in the uplift near its center. The crater is exposed to the surface, resulting in erosion. It is currently being worked as a quarry. == Description == The impact site is located east of Kentland, Indiana in Newton County. The disturbance is in diameter. The bedrock has a thin layer of glacial till, with a maximum depth of in the depression ring. The bedrock around the impact structure is generally flat with a slight dip towards the southwest and the Illinois Basin. The upper layers are Lower Mississippian from the Carboniferous period and Upper Devonian are relatively flat throughout this area of Indiana with the exception of impact site.〔Landy, R.T. and W.R. Van Schmus; A structural study of the Kentland, Indiana Impact site; Dept of Geology, University of Kansas; Lawrence, Kansas’ 1978〕 The core of the site is Ordovician rocks in the Prairie Du Chien through Maquoketa Groups. Surrounding the core is Silurian rocks of Sexton Cr Dolomite and Kokomo Limestone. This uplifted core pierces the New Albany Shale of the Devonian age and the Mississippian age New Providence Shale and Rockford Limestone.〔Bjørnerud, MG.; Superimposed deformation in seconds: breccias form the impact structure at Kentland, Indiana (USA); Geology Dept., Lawrence University, Appleton, WI; 2997〕 Prior to quarry operations, research estimates that there has been of erosion since the initial event, followed by a shallow deposit of glacial till during the Wisconsin Glacial Period. The quarry operations have extracted the upper Ordovician carbonates of the Platteville and Galena (Prairie due Chien) groups along the northern edge of the since 1906.〔 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「Kentland crater」の詳細全文を読む スポンサード リンク
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