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Bonneterre Formation facts for kids

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Bonneterre Formation
Stratigraphic range: Guzhangian (Dresbachian)
~501–497Ma
Galena in dolostone (Bonneterre Dolomite, Upper Cambrian; Flat Rock, Old Lead Belt, Missouri, USA) 2 (40704497164).jpg
Galena in Bonneterre Dolomite (Upper Cambrian; Missouri)
Type Formation
Underlies Davis Formation
Overlies Lamotte Sandstone
Lithology
Primary Dolomite
Other Shale, limestone, sandstone
Location
Coordinates 37°38′10″N 90°34′41″W / 37.636°N 90.578°W / 37.636; -90.578Coordinates: 37°38′10″N 90°34′41″W / 37.636°N 90.578°W / 37.636; -90.578
Approximate paleocoordinates 22°54′S 86°30′W / 22.9°S 86.5°W / -22.9; -86.5
Region Illinois, Minnesota & Missouri
Country  United States

The Bonneterre Formation is an Upper Cambrian geologic formation which outcrops in the St. Francois Mountains of the Missouri Ozarks. The Bonneterre is a major host rock for the lead ores of the Missouri Lead Belt.

The Bonneterre Formation lies conformably on the Lamotte Sandstone and in places lies directly on the Proterozoic igneous core of the mountains. The Bonneterre is conformably overlain by the Davis Formation. In the outcrop area the Bonneterre has an average thickness of 375 to 400 feet. It is present in the subsurface throughout Missouri and has a maximum recorded thickness of 1580 feet under Pemiscot County in the Missouri Bootheel.

The formation is dominantly dolomite with areas or layers of pure limestone. A shaley or glauconitic zone occurs in the lower portion and the base contains sand and conglomerate or breccia where the formation overlaps the Lamotte and lies directly on the granite of the mountain core.

Fossil content

The formation has provided fossils of:

Monoplacophora

  • Hypseloconus bonneterrense
  • Irondalia
I. irondalensis
  • Kirengella washingtonense
  • Ulrichoconus
U. bonneterrense

Trilobites

  • Kingstoniidae
    • Blountia sp.
  • Tricrepicephalidae
    • Tricrepicephalus sp.

Gastropods

  • Tropidodiscidae
    • Strepsodiscus major
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