Bonneterre Formation

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.

Bonneterre Formation
Stratigraphic range: Upper Cambrian
Galena in Bonneterre Dolomite (Upper Cambrian; Missouri)
TypeFormation
UnderliesDavis Formation
OverliesLamotte Sandstone[1]
Lithology
PrimaryDolomite
OtherShale, limestone, sandstone[2]
Location
Coordinates37.636°N 90.578°W / 37.636; -90.578
CountryUnited States
ExtentIllinois, Minnesota, and Missouri

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.[2]

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.[2]

Paleofauna

Monoplacophora
  • Irondalia
I. irondalensis[3]
  • Ulrichoconus
U. bonneterrense[3]
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See also

References
  1. Thompson, Thomas L., 2001, Lexicon of Stratigraphic Nomenclature in Missouri, Missouri Department of Natural Resources, Division of Geology and Land Survey, Report of Investigation Number 73, p 37
  2. Howe, W. B. and J. W. Koenig, The Stratigraphic Section in Missouri, Missouri Geological Survey, 1961, pp. 15-18
  3. Stinchcomb, Bruce; Angeli, Nicholas (2002). "New Cambrian and Lower Ordovician monoplacophorans form the Ozark Uplift, Missouri". Journal of Paleontology. 76 (6): 965–974.


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