Decorah crater
{{Short description|470 million year old meteor crater in Iowa}}
{{Infobox terrestrial impact site
| name = Decorah crater
| other_name =
| photo = Decorah crater.jpg
| photo_size =
| photo_alt =
| photo_caption = Location of Decorah crater on bedrock map of Iowa
| map = United States
| map_alt =
| map_caption = Location of the crater in the United States
| map_size =
| location =
| label =
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| coordinates = {{coord|43|18|50|N|91|46|20|W|region:US|display=inline,title}}
| coordinates_ref =
| confidence = Potential{{citation |last=Mikheeva |first=Anna |year=2017 |title=The Complete Catalog of the Earth's Impact structures |url=http://labmpg.sscc.ru/impact/index1.html |publisher=Russian Academy of Sciences |pages=1 |accessdate=2017-10-14}}
| diameter = {{convert|3.5|mi|km|abbr=on}}
| depth =
| rise =
| imp_size =
| age = ~470 Ma
Middle Ordovician
| exposed = No
| drilled = No
| bolide = Ordovician meteor event?
| translation =
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| topo =
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| country = United States
| state = Iowa
| province =
| district = Winneshiek
| municipality = Decorah
}}
The Decorah crater, also called the Decorah impact structure, is a possible impact crater located on the east side of the city of Decorah in Iowa, United States. It is thought to have been caused by a meteor about {{convert|200|m|ft}} wide which struck during the Middle Ordovician Period, circa 470 million years ago.
Description
{{main|Iowa geology}}
The crater is estimated to be {{convert|3.5|mi|km}} in diameter, covered by the Winneshiek Shale.{{cite news|last=Vastag|first=Brian|title=Crater found in Iowa points to asteroid break-up 470 million years ago|url=https://www.washingtonpost.com/national/health-science/crater-found-in-iowa-points-to-asteroid-break-up-470-million-years-ago/2013/02/18/545131f8-76d5-11e2-aa12-e6cf1d31106b_story.html?wprss=rss_national|accessdate=19 February 2013|newspaper=The Washington Post|date=18 February 2013}}{{cite news|title=Geological survey: Ancient meteorite crater sits below Decorah|url=http://thegazette.com/2013/03/05/ancient-meteorite-crater-sits-below-decorah-geological-surveys-confirm/|accessdate=6 March 2013|newspaper=Cedar Rapids Gazette|date=5 March 2013}}{{cite web|last=US Geological Survey|title=Iowa Meteorite Crater Confirmed|url=http://www.usgs.gov/newsroom/article.asp?ID=3521|accessdate=7 March 2013}} There is no surface evidence of the impact, as the Winneshiek Shale is more than {{convert|50|ft|m}} below the bottom of the Upper Iowa River. The impact event, equivalent to 1,000 megatons of TNT, did not appear to penetrate the Earth's mantle, but it did push down the underlying Ordovician and Cambrian bedrock several hundred feet.{{Cite FTP |last=Iowa Department of Natural Resources|title=GEOLOGIC MAPPING FOR WATER QUALITY PROJECTS IN THE UPPER IOWA RIVER WATERSHED|url=ftp://ftp.igsb.uiowa.edu/igspubs/pdf/TIS-54.pdf|server=Technical Information Series No. 54, 2011|url-status=dead|accessdate=19 February 2013}} It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event, including three confirmed impact craters: Rock Elm crater in Wisconsin, Slate Islands crater in Lake Superior, and Ames crater in Oklahoma.{{cite journal|last=Heck|first=Philipp |author2=Birger Schmitz |author3=Heinrich Baur |author4=Alex N. Halliday|authorlink4 = Alexander Halliday |author5=Rainer Wieler |title=Fast delivery of meteorites to Earth after a major asteroid collision|journal=Nature|date=15 July 2004|volume=430|pages=323–325|issue=6997|doi=10.1038/nature02736|bibcode=2004Natur.430..323H|pmid=15254530}}
{{wide image|Decorah crater 2.jpg|500px||100%|center
|alt=Decorah crater}}
''Pentecopterus decorahensis''
The Middle Ordovician (Darriwilian) Winneshiek Lagerstätte sediments that filled in the crater contained a wide variety of unusual fauna. Among them was a newly discovered species of eurypterid, Pentecopterus decorahensis. Pentecopterus was scorpion-like in appearance, and the largest predator known from that time, measuring nearly 6 feet in length. Its species name was derived from "Decorah."{{cite journal|last1=Lamsdell|first1=James C.|author2=Derek E. G. Briggs|author3=Huaibao P. Liu|author4=Brian J. Witzke|author5=Robert M. McKay|title=The oldest described eurypterid: a giant Middle Ordovician (Darriwilian) megalograptid from the Winneshiek Lagerstätte of Iowa|journal=BMC Evolutionary Biology|date=2015|volume=15|issue=169|pages=169|doi=10.1186/s12862-015-0443-9|pmid=26324341|pmc=4556007 |doi-access=free |bibcode=2015BMCEE..15..169L }}
{{multiple image
|direction = horizontal
|align= left
|width1= 240
|width2= 240
|width3= 240
|image1=Decorah crater ARHIOWA00118726.jpg
|image2=USGS Decorah crater.jpg
|image3=Middle Ordovician craters.jpg
|caption1=Aerial photo of Decorah and the extent of the crater
|caption2=U.S. Geological Survey aerial resistivity map of the Decorah, Iowa area, showing the Decorah Impact Structure.
|caption3=North American Middle Ordovician impact craters, which may be part of the Ordovician meteor event. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Disturbance, 4: Slate Islands crater.
}}
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