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Regional Geology of North America

Central Lowlands Province

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The Central Lowlands Province include the parts of majority of the Midwestern States: Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Missouri, Ohio, Oklahoma, and Wisconsin. For most of the region, the landscape is a low mostly flat plain or low rolling hills cut by stream valleys. The region north of the Ohio and Missouri rivers was impacted by continental glaciers. The region is the also called the "Corn Belt" because nearly the entire region is utilized for agriculture. Most of the Central Lowlands north of the Ohio and Missouri Rivers were repeatedly covered by continental ice sheets (glaciatiations) during the Pleistocene Epoch. South of those rivers the land was mostly unglaciated.

The region is underlain by generally flat-lying sedimentary rocks with some anomalously larger structural basins that formed slowly and filled in with sediments throughout the Paleozoic Era. These include the Michigan Basin (encompassing most of the lower Michigan Peninsula between Lake Michigan and Lake Huron), the Illinois Basin (in southwestern Indiana and southern Illinois and Western Kentucky, and the Forest City Basin (extending from southern Iowa, eastern Kansas, western Missouri, and into Oklahoma) (see Figure 52). Compared with structural basins elsewhere in the west, these basins are relatively shallow—filled with several thousands of feet of sedimentary deposits. The center of these basins are capped with with coal-bearing sedimentary deposits that form cliffy sandstone escarpments in belts around portions of the basins. The Pennsylvanian sandstone layers form escarpments s that overly a thick sequence of Mississippian-age limestone formations that underlie the entire region (Figures 56 and 57). These limestones are host to the famous and extensive cavern systems in Kentucky, Indiana, and Missouri, including those in Mammoth Cave National Park.

The region is drained by the principle tributaries: the Ohio River and the Missouri River merge with the Mississippi River near St. Louis, forming the principle river drainage of the mid continent (Figures 60 and 61). Prior to the ice ages, rivers in the region may have drained northward toward Hudson Bay. The continental glaciers blocked the rivers, creating lakes that would fill and eventually breach into the next valley. The drainages consolidated into the Mississippi River system. The Mississippi Embayment region filled with sandy glacial outwash sediments, creating the extensive aquifer system in the lower Mississippi Valley.

Physiographic regions of Kentucky
Fig. 56. Physiographic regions of Kentucky.
The Dripping Springs escarpment in Mammoth Cave National Park in Kentucky.
Fig. 57. The Dripping Springs Escarpment of the Pennyroyal Plateau along the Green River in Mammoth Cave National Park in western Kentucky. The caverns are in Mississippian-age limestones.
Typical view of Indiana corn fields. Mississippi River in Wisconsin Confluence of the Misouri, Illinois, and Mississippi Rivers near St. Louis as viewed from satellite during floods of 2008. Satellite view of the confluence of the Mississippi and Ohio Rivers near Cairo, Illinois.
Fig. 58. An Indiana corn field represents a typical view of the landscape practically anywhere in the Central Lowlands Province of the Midwestern US. Fig. 59. View looking east from an escarpment along the western side of the Mississippi River looking toward the lowlands of southern Wisconsin. Fig. 60. Confluence of the Missouri, Illinois, and Mississippi Rivers near St. Louis as viewed from satellite during floods of 2008. Fig. 61. Satellite view of the confluence of the Mississippi and Ohio Rivers near Cairo, Illinois. Note the sediment color contrast of the two rivers. Fig. 61a. Glacial moraines (hills) and kettles (lakes) of central Wisconsin as seen from Lantham Peak State Park tower observatory in the northern Central Lowlands.     1/20/2020
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