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Hydrodynamic role of groundwater in bolide impact: Evidence from the Kentland structure, Indiana, USA*

Raymond C. Gutschick†
Raymond C. Gutschick†
Professor Emeritus of Geology, University of Notre Dame, Notre Dame, Indiana 46556, USA
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December 10, 2018
Publication history
13 August 2018


The extremely important role of groundwater has been largely overlooked in studies of meteorite and comet impact processes. Beyond the radius of plasma generation, impacts can produce massive shattering in saturated porous rocks. Fluid pressure rise reduces rock strength and facilitates hydrofracture, to produce intraformational monomict breccias, faulting, and generation of mobile polymict breccia slurries. Decompression of a deep “transient” crater accounts for complex central uplift and gravitational collapse of tremendous slide blocks that in turn cause injection and ejection of fluidized breccia. As pore fluid pressures equilibrate, frictional strength increases, and the structural form is locked into stability. Evidence is reported here for Kentland, Indiana, where quarry rocks display relatively low pressure-temperature (elastic to ductile transition, 100 kb–100 °C) impact phases of the model of D. Stöffler. Breccias include monomict, polymict, mixed polymict-fault, and conventional fault types. The monomict breccias are associated with aquifer beds and formed by pervasive shockwave transmission on impact. Polymict breccias are derived from all rock types and formed from late stage injection-ejection pseudoviscous slurries. These processes can apply to similar impacts like Wells Creek, Flynn Creek, Decaturville, Sierra Madre, and many others.

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GSA Special Papers

Ancient Oceans, Orogenic Uplifts, and Glacial Ice: Geologic Crossroads in America’s Heartland

Lee J. Florea
Lee J. Florea
Indiana Geological and Water Survey Indiana University 611 N. Walnut Grove Avenue Bloomington, Indiana 47405, USA
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Geological Society of America
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December 10, 2018




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