United States Meteorite Impact Craters


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Calvin impact CRATER, Michigan

Calvin Impact Crater, Michigan

The Calvin Impact Structure, located in Cass County, Michigan, is 8.5 km in diameter. It is not exposed to the surface.  The structure dates from the Ordovician, about 450 million (+- 10) years ago.

Diagnostic Evidence For This Crater

The impact origin of each location listed on this website has been supported by unambiguous diagnostic evidence of hypervelocity impact that has been reported in a scientific (usually peer reviewed) context.  Without such evidence, a geological structure is not a confirmed impact crater.  This section, which is included for each crater on this website, is not an exhaustive list of such published evidence, but is meant to demonstrate that appropriate work has been done for each listing.

Nature of diagnostic evidence:

  • I have found no published example of diagnostic evidence of hypervelocity impact for this location.

Other reported evidence: morphology, 'microbreccia,' iron oxide and iron sulfide microspherules, single sets of planar fractures in a percentage of quartz grains.

Other related publications:

Donofrio, R.R., 1998, North American impact structures hold giant field potential: Oil and Gas Journal, v. 96/19.

Milstein, R. L., The Calvin 28 structure: Evidence for impact origin. Canadian Journal of Earth Sciences, v. 25, pp. 1524-1530. 1988.
Milstein, R. L., Impact origin of the Calvin 28 cryptoexplosive distrunbance, Cass County, Michigan. Michigan Department of Natural Resources, Geological Survey Division, v. Report of Investigation 28, pp. 1-33. 1988.
Milstein, R. L., The Calvin impact crater, Cass County, Michagan: Identification and anlaysis of a subsurface Ordovician astrobleme. Ph. D. Ph.D. Thesis, Oregon State University, 86. 1994.
 (this links to the full text at -->)
Milstein, R. L., The Calvin 28 cryptoexplosive distrubance, Cass County, Michigan. Geological Society of America Centennial Field Guide - North-Central Section, pp. 315-320. 1987.

R. L. Milstein.  Geology of the Calvin Impact Structure, Cass County Michigan






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