The Kaskaskia sequence was a cratonic sequence that began in the mid-

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

, peaked early in the

Mississippian Mississippian may refer to: * Mississippian (geology), a subperiod of the Carboniferous period in the geologic timescale, roughly 360 to 325 million years ago *Mississippian culture, a culture of Native American mound-builders from 900 to 1500 AD ...

, and ended by mid-Mississippian time. A major

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

separates it from the lower Tippecanoe sequence. The basal—that is, the lowest and oldest—units of the Kaskaskia consist of clean

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

eroded from the Appalachian orogenic belt to the east, the

Ozark Dome 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 porti ...

in the center of the continent, and south from the

Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the anc ...

. These sandstones are followed by extensive

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

s, though these are often difficult to distinguish from preceding Tippecanoe carbonates. The Kaskaskia is well known for its widespread carbonate and

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

strata, which in fact compose most of the rocks; the Williston Basin in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...

is a superb example of such evaporite deposits. Beginning in the late Devonian, black shales begin to dominate in the rocks, composed of detritus eroded from the uplifted Acadian highlands to the west; they also indicate widespread anoxic conditions across the sea floor. By mid-Mississippian time however, shallow-water carbonate deposition resumed, until the final

regression Regression or regressions may refer to: Science * Marine regression, coastal advance due to falling sea level, the opposite of marine transgression * Regression (medicine), a characteristic of diseases to express lighter symptoms or less extent ( ...

of the epeiric seas late in the period.

References

*Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution, 2nd ed. Belmont: West Publishing Company, 1997. (pp. 539–44) Devonian United States Mississippian United States Carboniferous Canada Devonian Canada Carboniferous System of North America Devonian System of North America Mississippian Series {{Canada-geologic-formation-stub