Glover Bluff - Hypervelocity Impact Crater

Alternate Names
Local Language
Coordinates 43° 58' 3" N; 89° 32' 18" W
Notes
  1. Central Wisconsin, Marquette County.
Country United States of America
Region Wisconsin
Date Confirmed 1983
Notes
  1. Confirmed by "shatter cones from the north hill" (Read, 1983).
Buried? No
Notes
  1. Glacial drift covers some of the crater-fill products (Read, 1985).
Drilled? Yes
Notes
  1. Water wells in the area reveal conspicuously white sandstone thought to be crater breccia and uplifted Cambrian sandstones (Read, 1985).
Target Type Sedimentary
Notes
  1. Ordovician and Cambrian sandstone and dolomite (Cannon and Mudrey, 1981).
Sub-Type Dolomite, Sandstone
Apparent Crater Diameter (km) 8 km
Age (Ma) <485
Notes :
  1. A rough range of <485 Ma is provided by stratigraphic age constraints (Read, 1983). The youngest rocks known to have been disrupted during crater formation are Lower Ordovician (Read, 1985). Shatter cones are found in the Lower Ordovician dolomite (Read, 1984).

Method :
  1. Stratigraphy
Impactor Type Unknown

Advanced Data Fields

Notes

Erosion
5
Final Rim Diameter
Unknown
Apparent Rim Diameter
8 km
  1. Dimensions are poorly known. See (Cannon and Mudrey, 1981) and (Read, 1984).
Rim Reliability Index
3
  1. Three hills are grouped in a roughly circular area ~500 m in diameter. Surrounding these hills, strata has been dropped ~60 m relative to the surrounding undisturbed area (Cannon and Mudrey, 1981). No reference to a raised rim.
Crater Morphology
Complex
Central Uplift Diameter
km
Central Uplift Height
Unknown
Uplift Reliability Index
3
Structural Uplift
Unknown
Thickness of Seds
Target Age
Palaeozoic
Marine
No
Impactor Type
Other Shock Metamorphism
No
Shatter Cones
Yes
  1. Well-developed shatter cones in lower Ordovician dolomite; few exceed 8 cm in lenght (Read, 1983). A shatter cone sample 9 cm long is illustrated in the paper by (Coleman, 2001).
Planar Fractures
No
Planar Deformation Features
No
Diaplectic Glass
Yes
  1. The pellets appear to be crystallized glass which solidified in midair from melt droplets" via (Read et al., 1984).
Coesite
No
Stisovite
No
Crater Fill
Proximal Ejecta
Distal Ejecta
Dykes
Volume of Melt
Depth of Melting

References

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G L Ekern, F T Thwaites (1930) The Glover Bluff structure, a disturbed area in the Paleozoics of Wisconsin, Transactions of the Wisconsin Academy of Sciences, Arts and Letters 25, p. 89-97, Wisconsin Academy of Sciences, Arts and Letters, Madison, WI, pdf

W F Read (1983) Shatter cones at Glover Bluff, Wisconsin, Meteoritics 18(3), p. 241-243, Arizona State University, Center for Meteorite Studies, Tempe, AZ, url

W F Read (1984) The circular structure at Glover Bluff: What and where it is, Meteoritics 19(4), p. 295-296, Arizona State University, Center for Meteorite Studies, Tempe, AZ, url

W F Read (1985) Impact bombs, probably from the Glover Bluff crater, in middle Ordovician marine sediments of southeastern Wisconsin, Abstracts with Programs - Geological Society of America 17(5), p. 322, Geological Society of America (GSA), Boulder, CO

W F Read, L Bowman, R Dotson, K Hrametz, T McCasey (1985) Impact bombs in middle Ordovician marine sediments of southeastern Wisconsin, Abstracts of Papers Submitted to the Lunar and Planetary Science Conference 16, Part 2, p. 687-688, Lunar and Planetary Science Conference, Houston, TX, url

W F Read (1986) Ejecta from the Glover Bluff crater, or other craters of the same age, NASA Technical Memorandum 88383, p. 476, National Aeronautics and Space Administration (NASA), Washington, DC

R S Dietz, J F McHone (1991) Astroblemes recently confirmed with shatter cones, Meteoritics 26(4), p. 332, Tempe, AZ, United States (USA): Arizona State University, Center for Meteorite Studies, Tempe, AZ, url

L D Coleman (2001) A meteorite crater in the backyard, Meteorite 7, p. 8-11, url

B Ernst, D J Lehrmann (2010) The Glovers Bluff structure, a possible impact feature exposed in the Mid-continent Cambro-Ordovician strata of central Wisconsin, Abstracts with Programs - Geological Society of America 42(2), p. 91, Geological Society of America (GSA), Boulder, CO

B Ernst, T Paulsen (2011) New constraints on the timing of deformation at the Glover Bluff structure near Coloma, WI from a calcite twinning analysis, Abstracts with Programs - Geological Society of America 43(5), p. 188, Geological Society of America (GSA), Boulder, CO, url

G M Renard (2011) Ejecta strata of recent origin have been identified in central Wisconsin at Glover Bluff impact site, Abstracts with Programs - Geological Society of America 43(5), p. 306, Geological Society of America (GSA), Boulder, CO, url