The Kentland structure, also known as the Kentland crater or the Kentland disturbed area, is an

impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface ...

located near the town of Kentland in

Newton County, Indiana Newton County is a county located near the northwestern corner of the U.S. state of Indiana. As of 2010, the population was 14,244. This county is part of Northwest Indiana as well as the Chicago metropolitan area. The county seat is Kentla ...

, United States. It was discovered about 1880 when two farmers began to

quarry A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their envi ...

crushed rock there. The presence of

shatter cone Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the rang ...

s and deformed

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

led geologists to conclude by the late 1960s that the Kentland structure is a deeply eroded

, rather than

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

in origin. Deformation at the site is so great that vertical contacts between normally horizontal rock formations of different ages are common. The structure itself is a circular

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

, about in diameter, deeply eroded and buried in

glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

debris. Its age is estimated to be less than 97 million years (

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

or younger). The Shakopee dolomite at the center of the structure is about 450 million years old (

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

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

Period of the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

Era * ‘"300 MYA‘''= Bzhelian or Late Pennsylvanian Epoch (

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

Period) of the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

EraCochise College web-page, December 18, 2012 This impact structure was studied in 1978. John Weber and his associates presented

fission track dating Fission track dating is a radiometric dating technique based on analyses of the damage trails, or tracks, left by fission fragments in certain uranium-bearing minerals and glasses. Fission-track dating is a relatively simple method of radiomet ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

from this impact structure.

Society for Sedimentary Geology The Society for Sedimentary Geology is an international not-for-profit, scientific society based in Oklahoma. It is commonly referred to by its acronym SEPM, which refers to its former name, the Society of Economic Paleontologists and Mineralogists. ...

(SEPM) Research Conference, "The Sedimentary Record of Meteor Impacts" (21–23 May 2003,

Springfield, Missouri Springfield is the third largest city in the U.S. state of Missouri and the county seat of Greene County. The city's population was 169,176 at the 2020 census. It is the principal city of the Springfield metropolitan area, which had an estimat ...

)

Coesite Coesite is a form ( polymorph) of silicon dioxide Si O2 that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first synthesized by Loring Coes Jr., a chemist at the ...

and

s are found in the uplift near its center. The impact structure is exposed to the surface, resulting in erosion. It is currently being worked as a quarry.

Description

Kentland structure - Laney - Schmus fig 2b (large)

The impact site is located east of Kentland,

Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...

, 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 Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky. The basin is elongate, extending app ...

. The upper layers are Lower Mississippian from the

period and Upper

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

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

rocks in the Prairie du Chien through Maquoketa Groups. Surrounding the core is

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

rocks of Sexton Cr

Dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

and Kokomo

Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

. This uplifted core pierces the New Albany

Shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

of the

age and the

Mississippian age The Mississippian ( , also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughly ...

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 since 1906.

Structure

The structure is a deeply eroded

complex crater Complex craters are a type of large impact crater morphology. Above a certain threshold size, which varies with planetary gravity, the collapse and modification of the transient cavity is much more extensive, and the resulting structure is call ...

. Since the original impact, the structure has eroded over , eliminating the crater and other surface elements. ; Ring anticline The ring surrounds the impact site, separating it from the surrounding flat-lying regional bedrock. The ring is about in radius around the central disconformity. ; Ring depression The ring depression is the result of the displacement of materials at lower levels to fill the void created as the central uplift rose. Studies at other sites similar to the Kentland structure have found the depression to be the equivalent of the material that would have moved under the uplift as it occurred. ; Central Uplift A cross section of the uplift, beginning on the outer edge, moving towards the middle, is shown in the image above.

References

Additional sources

*Cohen, A.J., Bunch, T.E., and Reid, 1961, Coesite discoveries establish cryptovolcanics as fossil meteorite craters: Science, v.134, p. 1624-1625. * Collet, J., 1883, Geological survey of Newton County: Ind. Dept Geol. and Nat. Hist., 12th Ann. Report, p. 58-59. *Dietz, R.S., 1947, Meteorite impact suggested by orientation of shatter cones at the Kentland, Indiana, disturbance: Science, v.105, n.2714, p. 42-43. *Dietz, R.S., 1960, Meteorite impact suggested by shatter cones in rock: Science, v.131, n.3416, p. 1781-1784. *Dietz, R.S., 1963, Cryptoexplosion structures-a discussion: Am. Jour. Sci., v.261, p. 650-664. *Dietz, Robert S.; Shatter Cones in Cryptoexplosion Structures (Meteorite Impact?); The Journal of Geology; Vol. 67, No. 5 (Sep., 1959), pp. 496–505 *Gutschick, R. C., Geology of the Kentland dome structurally complex anomaly, northwestern Indiana (Field Trip 5). Field trip in Midwestern Geology, Annual Meeting, Geological Society of America, Indianapolis, v. 1, pp. 105–138. 1983. *Gutschick, R. C., Geology of the Kentland structural anomaly, northwestern Indiana—update. Purdue University, Department of Geosciences, and Geological Society of America, North-central Section, Guidebook 4, 38 p. 1982. *Gutschick, R.C., 1976, Geology of the Kentland structural anomaly, northwestern Indiana: Guidebook for 1976, North-Central GSA Meeting, 59 p. *Gutschick, R. C., Geology of the Kentland impact structural anomaly. Meteoritical Society, 35th Annual Meeting, Guidebook for Field Trip. 1972. *Gutschick, R. C., Geology of the Kentland impact structural anomaly, northwestern Indiana. Shaver, R.H. and Sunderman, J.A., eds., Field Guide for the National Association of Geology Teachers, East-central Section, 20 p. 1971. *Gutschick, R. C., The stratigraphy and structure of the Kentland impact anomaly, Indiana (abstract). The Geological Society of America, v. 2, pp. 564–565. 1970. *Gutschick, R. C., The Kentland structural anomaly, Indiana. Geology from Chicago to Cincinnati, Geological Society of America Guidebook for Field Trips, v. 2, pp. 12–17. 1961. * Laney, R.T., and W.R. Vanschmus, 1978. "A structural study of the Kentland, Indiana impact site" in ''Lunar and Planetary Science'' 9, pp 627–629. * Mark J. Camp and Graham T. Richardson, ''Roadside Geology of Indiana'', (Mountain Press Publishing Co.: Missoula, Montana, 1999), pp. 215–216.

External links

Archived Bibliography for Kentland CraterAbstract: Geochemical Study of Rocks from the Kentland, Indiana, Impact StructureAbstract: Structural Study of the Kentland, Indiana, Impact SiteAbstract: John C. Weber et al., "The Kentland Impact Crater, Indiana (USA): An Apatite Fission-Track Age Determination Attempt", in Christian Koeberl and Herbert Henkel (eds.) ''Impact Tectonics'', Berlin and Heidelberg: Springer, 2005, pp. 447-466.

United States Meteorite Impact Craters: Kentland Crater, IndianaInterview with Purdue University Professor Jay Melosh about Kentland CraterExploration of the Kentland Impact Structure
{{Impact cratering on Earth Impact craters of the United States Cretaceous impact craters Landforms of Newton County, Indiana

Description

Structure

See also

References

Additional sources

External links