The Bonneterre Formation is an

Upper Cambrian The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three ...

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

which outcrops in the

St. Francois Mountains The St. Francois Mountains in southeast Missouri are a mountain range of Precambrian igneous mountains rising over the Ozark Plateau. This range is one of the oldest exposures of igneous rock in North America. The name of the range is spelled out ...

of the

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

Ozarks The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, is a physiographic region in the U.S. states of Missouri, Arkansas, Oklahoma and the extreme southeastern corner of Kansas. The Ozarks cover a significant port ...

. The Bonneterre is a major host rock for the

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April 2 ...

s of the Missouri Lead Belt. The Bonneterre Formation lies conformably on the

Lamotte Sandstone Lamotte, LaMotte or La Motte may refer to: Places Canada * La Motte, Quebec France * La Grande-Motte, in the Hérault département * La Motte, Côtes-d'Armor, in the Côtes-d'Armor ''département'' * La Motte, Var, in the Var ''département'' ...

and in places lies directly on the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

core of the mountains. The Bonneterre is conformably overlain by the

Davis Formation The Davis Formation is a geologic formation in Indiana and Missouri. It preserves fossils dating back to the Cambrian period. See also * List of fossiliferous stratigraphic units in Indiana * List of fossiliferous stratigraphic units in Missouri ...

. 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 Missouri Bootheel is a salient located in the southeasternmost part of the U.S. state of Missouri, extending south of 36°30′ north latitude, so called because its shape in relation to the rest of the state resembles the heel of a boot. ...

. The formation is dominantly

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

with areas or layers of pure

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

. A

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

y or

glauconitic Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () me ...

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 Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

of the mountain core.

Fossil content

The formation has provided fossils of:Bonneterre Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org

Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

* '' Hypseloconus bonneterrense''Stinchcomb, 1975 * '' Irondalia'' : ''I. irondalensis''Stinchcomb & Angeli, 2002 * '' Kirengella washingtonense'' * '' Ulrichoconus'' : ''U. bonneterrense''

Trilobites

* Kingstoniidae ** '' Blountia sp.'' * Tricrepicephalidae ** '' Tricrepicephalus sp.''

Gastropods

* Tropidodiscidae ** '' Strepsodiscus major''

References

Bibliography

* * {{Chronostratigraphy of Minnesota Geologic formations of Illinois Geologic formations of Minnesota Geologic formations of Missouri Cambrian System of North America Cambrian Missouri Cambrian Minnesota Cambrian Illinois Guzhangian Dolomite formations Reef deposits Cambrian northern paleotemperate deposits Paleontology in Missouri Landforms of the Ozarks St. Francois Mountains