Calvin - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 41° 49' 30" N; 85° 56' 40" W
Notes
  1. SW Michigan, 1.4 km S of the village of Calvin Center, Calvin Township, Cass County.
Country United States of America
Region Michigan
Date Confirmed 1994
Notes
  1. Confirmed by presence of PDFs in quartz (Milstein, 1994).
Buried? Yes
Notes
  1. Filled by 211 m of Silurian dolomite and evaporite overlain by 224 m of Devonian shale, limestone, and dolomite.
Drilled? Yes
Notes
  1. 8 deep test wells, no cores exist for rocks older than Devonian. 110 wells in 3 oil fields.
Target Type Sedimentary
Notes
  1. 0.533 km of Cambrian sandstone and sandy dolomite interspersed with shale in the upper and lower formations and 0.388 km of Ordovician shale, limestone, sandy dolomite, and minor amounts of cherty dolomite.
Sub-Type Dolomite, Limestone, Sandstone, Shale
Apparent Crater Diameter (km) 8.5 km
Age (Ma) 444 - 458
Notes :
  1. Minimum age: Late Ordovician (Cincinnatian) units overly the impact (Millstein, 1994) Maximum age: Ordovician target rocks (Millstein, 1994)

Method :
  1. Stratigraphy
Impactor Type Unknown

Advanced Data Fields

Notes

Erosion
5
  1. Formations in outer rim are 1.5 to 9 m higher than the same formations within the depression. Central dome of structure corresponds to the central uplift of crater (Milstein et al., 1988). No evidence for ejecta deposits or major crater-fill impactites.
Final Rim Diameter
Unknown
Apparent Rim Diameter
8.5 km
  1. (Milstein, 1994)
Rim Reliability Index
2
  1. Isolated feature involving intense, large-scale deformation in otherwise flat-lying strata. The structure is circular, with a central uplift, surrounding annular depression and a peripheral anticline (Milstein, 1994). Structural uplift from p11 of (Milstein 1994). Central uplift height measured from Figure 4; lowest of crater floor to max of peak (p8).
Crater Morphology
Complex
Central Uplift Diameter
1.8km
Central Uplift Height
~0.050
Uplift Reliability Index
2
Structural Uplift
400 m
Thickness of Seds
0.921
Target Age
Palaeozoic
Marine
No
Impactor Type
Other Shock Metamorphism
Yes
  1. Rhombohedral cleavage in quartz and also point-source radiating fractures, decreasing radially from centre of structure, noted by (Milstein 1994). Also observed: iron microspherules.
Shatter Cones
No
Planar Fractures
No
Planar Deformation Features
Yes
  1. PDF in quartz grains, single sets (Milstein, 1994).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
LB
  1. The test wells Hawkes-Adams 1-28, Lawson No. 1 and Smith No. 1-20 contain a polymict breccias (Milstein, 1994). Crater is deeply buried and good core of the basement rock is not available, see (Milstein 1994) and (Ghatge 1984).
Proximal Ejecta
Distal Ejecta
Dykes
Volume of Melt
Depth of Melting

References

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R L Milstein (1987) The Calvin 28 cryptoexplosive disturbance, Cass County, Michigan, North-central section of the Geological Society of America, Donald L Biggs (ed.), Geol. Soc. Am., Boulder, CO, url

R L Milstein (1988) The Calvin 28 Structure; evidence for impact origin, Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre 25(9), p. 1524-1530, National Research Council of Canada, Ottawa, ON, url, doi:http://dx.doi.org/10.1139/e88-143

R L Milstein (1994) The Calvin impact crater, Cass County, Michigan: Identification and analysis of a subsurface Ordovician astrobleme, ProQuest Dissertations and Theses, p. 123-123 p., Ann Arbor: Oregon State University, url

R L Milstein (1996) The Calvin impact crater and its associated oil production, Cass County, Michigan, Annual Meeting Expanded Abstracts - American Association of Petroleum Geologists 5, p. 99, American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists, Tulsa, OK, url

R L Milstein (1997) The Calvin impact structure, Cass County, Michigan; identification and analysis of a subsurface Ordovician astrobleme, Circular - Oklahoma Geological Survey 100, Kenneth S Johnson, Jock A Campbell (ed.), p. 391-393, Norman, OK, United States (USA): University of Oklahoma, Norman, OK, url

R L Milstein (2001) Geology of the Calvin impact structure, Cass County, Michigan, AAPG Bulletin 85(8), p. 1536-1537, American Association of Petroleum Geologists, Tulsa, OK, url

R V Brady (2002) A comparison of two possible astroblemes in southern Michigan; the Ordovician age Calvin & Reading cryptoexplosive structures, Michigan Academician 34(1), Kathleen F Duke (ed.), p. 39, Michigan Academy of Science, Arts and Letters, Ann Arbor, MI, url

Jens Ormö, M Lindstrom (2004) Does the marine-target crater record reflect an increased cosmic bombardment during the Middle Ordovician?, Abstracts with Programs - Geological Society of America 36(5), p. 321, Geological Society of America (GSA), Boulder, CO, url