Mississippian Period (359 to 323 million years ago)
Sedimentary rocks of Mississippian age in North America are dominated by marine sediments preserved as limestones rock formations when shallow, warm seas covered much of North America. Massive fossiliferous limestone rock formations of Mississippian age exposed throughout the Midcontinent (Mississippi Valley), and throughout the Appalachian and Rocky Mountain regions (Figure 2.31). For example, the Redwall Limestone in the Grand Canyon region is about 800 feet thick (Figure 2.32). Mississippian rocks throughout these regions are host to many cavern systems (such as Mammoth Cave in Kentucky). Mississippian rocks are part of the Kaskaskia Sequence (see Figure 13.16).
The southern Appalachian Mountains began to rise in Mississippian time, and terrestrial lowlands and coastal swamps began to replace shallow seas on the North American continent. Coastal swamps along the margins of rising mountain ranges rising above the shallow seas began to support forests. Amphibians became the dominant marginal-land vertebrates in Mississippian time (they still requires water to lay their eggs).
|Figure 2.31. Mississippian Period marine invertebrate fossils from Pennsylvania.
|Figure 2.32. The massive Redwall Limestone of Marble Canyon and the Grand Canyon formed in the Mississippian Period.