Kentland crater
The Kentland Crater is an impact crater that was caused by a meteorite in the US state of Indiana more than 97 million years ago.
location
The Kentland crater, in English as a structure Kentland or Kentland disturbed area called, is located on Highway 24 toward Goodland of the city, 4 kilometers east Kentland , Indiana, United States . The crater structure covers the southwest of Newton County and the northwest of Benton County .
history
The impact structure was discovered in 1880 when two farmers were preparing to mine the pending shattered rock. As early as 1883, Collett reported on the unusual storage conditions. At that time, he had already noticed cones of rays , which he had still viewed as a cone-in-cone structure . In 1947, Dietz's beam cones were definitely recognized as such for the first time. This discovery prompted the local geologists to interpret the structure as a meteorite crater and not, as in the past, of volcanic origin. The deformation in the vicinity of the crater was so strong that originally horizontally lying layer assemblies now showed perpendicular, abnormal contacts.
description
Structural structure
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The Kentland Structure is a deeply eroded complex crater that has removed up to 300 meters of sediment, completely removing the former impact crater and other surface elements. The structure originally consisted of a central mountain, a ring-shaped depression and an anticlinal ring wall. The two rings, together 6.2 kilometers wide, separate the central part from the surrounding flat-lying sediments. The ring-shaped depression was created when the central mountain was pressed out and material therefore moved out of the ring area towards the center. The illustration opposite shows a profile through the central mountain.
geology
The Kentland Crater is a circular dome bulge that is 7,240 meters in diameter. The structure has been severely eroded and filled with 15 to a maximum of 40 meters thick glacial deposits . The impact occurred in flat-lying Paleozoic sediments , which range from the middle Ordovician to the Lower Carboniferous ( Pennsylvania ) and are mainly composed of carbonates, shale clays and sandstones.
The approximately 450 million year old Shakopee Dolomite from the Ordovician in the center has been raised up to 600 meters from its normal position. The Ordovician classes belong to the Prairie du Chien Group up to the Maquoketa Group . The core area is surrounded by formations of the Silurian, such as the Sexton Creek Dolomite or the Kokomo Limestone . Stratigraphically higher layers come from the Upper Devonian ( New Albany Shale ) and the lower Lower Carboniferous ( New Providence Shale and Rockford Limestone ). They are pierced by the pressed out core area. Normally the Paleozoic sediments lie flat in the entire state of Indiana with a slight dip to the southwest towards the Illinois Basin , only on the Kentland structure they are extremely distorted.
The disturbed zone measures a total of around 12.5 kilometers in diameter. It is believed that 300 meters of overburden has been removed since the impact before the ground moraines of the Wisconsin glaciation overlaid. In today's quarry, which has been in operation since 1906, the Ordovician carbonate rocks of the Platteville Group and the aforementioned Prairie du Chien Group (or Galena Group) are exposed on the north side .
Impact structures
In the center of the crater, radiation cones and remnants of Coesite in the Ordovician St. Peter Sandstone of the central pressing have been found on impact structures .
Planar deformation lamellae (PDFs), breccias , megabreccias and very complex deformation patterns are further indications of an over-rapid impact . Furthermore, the morphology, drill cores, geological mappings and profiling indicate an impact.
Age
No absolute age determinations have yet been made at the Kentland crater. The relative age of the structure is estimated to be less than 300 million years BP (Upper Carboniferous, Gzhelian ) and older than 97 million years BP ( Upper Cretaceous , Cenomanian ).
See also
literature
- Bell, MS and Sharpton, VL: High-pressure shock effects in silica in St. Peter sandstone from the Kentland impact structure, Indiana, USA (abstract) . In: Meteoritics & Planetary Science . Volume 31, 1996, pp. A13 (English).
- Koeberl, C. and Sharpton, VL: Geochemical study of rocks from the Kentland, Indiana, impact structure: Progress report (abstract) . In: Meteoritics . Vol. 28, No. 3 , 1993, p. 382 (English).
- Morrow, JR and Weber, JC 2009: Comparison of Low-Pressure Shock-Metamorphic Effects in Quartz from Barringer Crater, Arizona, and Kentland Dome, Indiana (abstract) . In: 40th Lunar and Planetary Science Conference . 2009 (English).
- Weber, JC, Poulos, C., Donelick, RA, Pope, MC and Heller, N .: The Kentland Impact Crater, Indiana (USA): An Apatite Fission-Track Age Determination Attempt . In: Koeberl, C. and Henkel, H. (Eds.): Impact Tectonics . Springer Berlin Heidelberg, 2005, p. 447-466 (English).
Individual evidence
- ^ Collett, J: Geological Survey of Newton County . In: Indiana Department of Geology and Natural History, 12th Annual Report . 1883, p. 58-59 .
- ^ A b Dietz, RS: Meteorite impact suggested by the orientation of shatter-cones at the Kentland, Indiana disturbance . In: Science . tape 105 , 1947, pp. 42-43 , doi : 10.1126 / science.105.2715.42 .
- ↑ Shrock, RR and Malott, CA: The Kentland area of disturbed Ordovician rocks in northwestern Indiana . In: Journal of Geology . Vol. 41, 1933, pp. 337-370 .
- ↑ Bjørnerud, M .G .: Superimposed deformation in seconds: breccias form the impact structure at Kentland, Indiana (USA) . Geology Dept., Lawrence University, Appleton, WI 1997.
- ↑ Laney, RT and WR Van Schmus: A structural study of the Kentland, Indiana Impact site . Dept of Geology, University of Kansas, Lawrence, Kansas 1978.
- ↑ Cohen, AJ, Bunch, TE and Reid, AM: Coesite discoveries establish cryptovolcanics as fossil meteorite craters . In: Science . Vol. 134, 1961, pp. 1624-1625 .
Coordinates: 40 ° 45 ′ 0 ″ N , 87 ° 24 ′ 0 ″ W.