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The Decorah structure, northeastern Iowa: Geology and evidence for formation by meteorite impact

2018; Geological Society of America; Volume: 130; Issue: 11-12 Linguagem: Inglês

10.1130/b31925.1

1943-2674

Bevan M. French, Robert M. McKay, Huaibao P. Liu, Derek E. G. Briggs, Brian J. Witzke,

Geology and Paleoclimatology Research

Research Article| August 08, 2018 The Decorah structure, northeastern Iowa: Geology and evidence for formation by meteorite impact Bevan M. French; Bevan M. French 1Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20013-7012, USA Search for other works by this author on: GSW Google Scholar Robert M. McKay; Robert M. McKay § 2Iowa Geological Survey, IIHR—Hydroscience & Engineering, University of Iowa, 340 Trowbridge Hall, Iowa City, Iowa, 52242, USA §Corresponding author: rjmckayic@gmail.com. Search for other works by this author on: GSW Google Scholar Huaibao P. Liu; Huaibao P. Liu 2Iowa Geological Survey, IIHR—Hydroscience & Engineering, University of Iowa, 340 Trowbridge Hall, Iowa City, Iowa, 52242, USA Search for other works by this author on: GSW Google Scholar Derek E.G. Briggs; Derek E.G. Briggs 3Department of Geology and Geophysics, and Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520, USA Search for other works by this author on: GSW Google Scholar Brian J. Witzke Brian J. Witzke 4Department of Earth and Environmental Sciences, University of Iowa, 121 Trowbridge Hall, Iowa City, Iowa 52242, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Bevan M. French 1Department of Paleobiology, Smithsonian Institution, Washington, D.C. 20013-7012, USA Robert M. McKay § 2Iowa Geological Survey, IIHR—Hydroscience & Engineering, University of Iowa, 340 Trowbridge Hall, Iowa City, Iowa, 52242, USA Huaibao P. Liu 2Iowa Geological Survey, IIHR—Hydroscience & Engineering, University of Iowa, 340 Trowbridge Hall, Iowa City, Iowa, 52242, USA Derek E.G. Briggs 3Department of Geology and Geophysics, and Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520, USA Brian J. Witzke 4Department of Earth and Environmental Sciences, University of Iowa, 121 Trowbridge Hall, Iowa City, Iowa 52242, USA §Corresponding author: rjmckayic@gmail.com. Publisher: Geological Society of America Received: 07 Sep 2017 Revision Received: 01 May 2018 Accepted: 19 Jun 2018 First Online: 08 Aug 2018 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2018 Geological Society of America GSA Bulletin (2018) 130 (11-12): 2062–2086. https://doi.org/10.1130/B31925.1 Article history Received: 07 Sep 2017 Revision Received: 01 May 2018 Accepted: 19 Jun 2018 First Online: 08 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bevan M. French, Robert M. McKay, Huaibao P. Liu, Derek E.G. Briggs, Brian J. Witzke; The Decorah structure, northeastern Iowa: Geology and evidence for formation by meteorite impact. GSA Bulletin 2018;; 130 (11-12): 2062–2086. doi: https://doi.org/10.1130/B31925.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Decorah structure, recently discovered in northeastern Iowa, now appears as an almost entirely subsurface, deeply eroded circular basin 5.6 km in diameter and ∼200 m deep, that truncates a near-horizontal series of Upper Cambrian to Lower Ordovician platform sediments. Initial analysis of geological and well-drilling data indicated characteristics suggestive of meteorite impact: a circular outline, a shallow basin shape, discordance with the surrounding geology, and a filling of anomalous sediments: (1) the organic-rich Winneshiek Shale, which hosts a distinctive fossil Lagerstätte, (2) an underlying breccia composed of fragments from the surrounding lithologies, and (3) a poorly known series of sediments that includes shale and possible breccia. Quartz grains in drill samples of the breccia unit contain abundant distinctive shock-deformation features in ∼1% of the individual quartz grains, chiefly planar fractures (cleavage) and planar deformation features (PDFs). These features provide convincing evidence that the Decorah structure originated by meteorite impact, and current models of meteorite crater formation indicate that it formed as a complex impact crater originally ∼6 km in diameter. The subsurface characteristics of the lower portion of the structure are not well known; in particular, there is no evidence for the existence of a central uplift, a feature generally observed in impact structures of comparable size. The current estimated age of the Decorah structure (460–483 Ma) suggests that it may be associated with a group of Middle Ordovician impact craters (a terrestrial "impact spike") triggered by collisions in the asteroid belt at ca. 470 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.