Chapter 11 Late Paleozoic Events Paleozoic overview Paleozoic Era • Early Paleozoic = Cambrian, Ordovician and Silurian • Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and Permian Carboniferous • Mississippian and Pennsylvanian Periods are also referred to with one name - Carboniferous Period. • Large plants (including spore-bearing trees and seed ferns) colonized the land during Late Paleozoic. Accumulation of plant remains in swamps produced the vast coal deposits for which Carboniferous was named. Late Paleozoic Orogenies, eastern N. America 1. Acadian orogeny and Caledonian orogeny 2. Alleghanian orogeny Late Paleozoic Orogenies, eastern N. America 1. Acadian orogeny and Caledonian orogeny – Middle Silurian to Middle Devonian. – Laurentia (North America) and Baltica (Europe) collide to form Laurasia. – A volcanic island arc (Avalon terrane) collides with eastern North America. Late Paleozoic Orogenies, eastern N. America 2. Alleghanian orogeny – Late Carboniferous – Gondwana (the southern continents, Africa, South America, India, Australia, Antarctica) and Laurasia collide. – Southern Appalachian mountains form as Laurasia collides with northwestern Africa (part of Gondwana). Late Paleozoic Orogenies, eastern N. America • The Acadian and Alleghanian orogenies were the result of the closure of the Iapetus Ocean and continental collisions which resulted in the formation of the supercontinent Pangea. Physiographic provinces of the Appalachian region in eastern North America. The Alleghanian orogeny The Alleghanian orogeny produced folds and large thrust faults in the southern Appalachians. Many folds are overturned to the northwest, and thrust faults dip to the southeast. Late Paleozoic Orogenies of west N. America • In the western part of North America, the Antler orogeny began during Devonian with the subduction of oceanic lithosphere beneath the western margin of the continent. • The Antler Orogeny continued into Mississippian and Pennsylvanian. • A volcanic island arc collided with the western margin of North America, crushing sediments and causing thrust faulting (Roberts Mountains Thrust Fault of Nevada). • Continental rise and slope deposits were thrust as much as 80 km over shallow water sediments of the former continental shelf. Late Paleozoic Sedimentary Sequences • Shallow epicontinental seas transgressed and regressed across Laurasia (North America) during Late Paleozoic as the glaciers melted and enlarged. • These sequences are bounded by (or separated by) unconformities. North American cratonic sequences Green = sedimentary deposits Yellow = missing strata associated with unconformities Acadian Orogeny • The effects of the Acadian orogeny are seen in a belt extending from Newfoundland to West Virginia, where thick sequences of sedimentary rocks are interbedded with rhyolitic volcanic rocks and granitic intrusions. Laurentia (North America) and Baltica (Europe) collide to form Laurasia. Devonian Paleogeography • The Acadian highlands in eastern North America (orange), form a continuous belt with the Caledonian Mountains adjacent to Greenland and Europe. • Erosion of these mountains resulted in the deposition of the Catskill Red beds in the Appalachian area, and the Old Red Sandstone in Europe. • Isopach (sediment thickness) and lithofacies map of Upper Devonian in the eastern U.S. • The Catskill clastic wedge sediments are thicker and coarser in the east. • The sediments become finer-grained westward, away from the Acadian highland source area. Williston Basin • In the Williston Basin area (South Dakota, Montana, and adjacent Canada), extensive reefs formed. • Restricted circulation within the reef-encircled basin led to the deposition of thick evaporite deposits. • The reefs of the Williston Basin provided permeable structures into which petroleum migrated, forming rich oil fields. Carboniferous In North America, Carboniferous consists of two periods: Mississippian and Pennsylvanian. – Mississippian is Early Carboniferous. – Pennsylvanian is Late Carboniferous. Mississippian • The name "Mississippian" is derived from exposures of rock in the valley region of the Mississippi River. • Mississippian sedimentary deposits contain abundant limestone with fossils of crinoids, blastoids, bryozoans, and fusulinid foraminifera. Pennsylvanian • Pennsylvanian rocks are dominated by coal-rich sediments that were deposited in swamps and deltas. • Coal deposits are particularly well developed in Pennsylvania. Mississippian Paleogeography Landmass in eastern North America and Europe (yellow), formed as the mountains (orange) eroded after Caledonian and Acadian orogenies. • Although a large mountain range was present in the Appalachian area, another orogeny was soon to occur, as indicated by the arrows and the words "Africa approaching" along the right side of the map. • Much of North America was covered by a shallow epicontinental sea. • North America sat on the equator, so temperatures were warm. • Note the Antler highlands in the western U.S. Mississippian Sedimentary Deposits • As muddy sediment from the eroding highlands decreased, carbonate deposition became widespread in the warm, shallow Kaskaskia sea. • Mississippian limestones contain abundant crinoids, blastoids, bryozoans, and fusulinid foraminifera. • The widespread blanket of carbonate rocks deposited during this time is called the great Mississippian lime bank. • In places, Mississippian limestones are more than 700 m thick. Crinoids Mississippian Sedimentary Deposits • The Kaskaskia sea retreated from the craton at the end of Mississippian. • This event is marked by one of the most widespread unconformities in the world. This unconformity separates Mississippian from Pennsylvanian. • The overlying Pennsylvanian rocks were deposited under very different conditions. Iapetus Ocean closed • The Iapetus Ocean (or Proto-Atlantic), completely closed by Late Carboniferous. • Closure of the Iapetus Ocean disrupted global ocean circulation and caused currents to be diverted from the tropics to more polar areas, contributing to glaciation. .