Eighth Edition
by Harold L. Levin

Chapter 11 - page 1

Late Paleozoic Events

The Late Paleozoic Era

Late Paleozoic = Devonian, Mississippian, Pennsylvanian, and Permian

The Mississippian and Pennsylvanian periods are sometimes referred to as the Carboniferous.

Large plants (including spore-bearing trees and seed ferns) colonized the land during the Late Paleozoic.
Accumulation of plant remains in swamps produced the vast coal deposits for which the Carboniferous was named.

Major events of the Paleozoic Era.

Late Paleozoic Tectonic Setting

The supercontinent Pangea (from the Greek, meaning "all land") was gradually assembled as the continents collided during the Late Paleozoic.

The larger continents (such as North America) grew by the addition of island arcs and microcontinents around their edges.

Paleogeography of the Late Paleozoic

Continental collisions caused several orogenies or mountain-building events in eastern North America.

1. Acadian orogeny and Caledonian orogeny
   Middle Silurian to middle Devonian.
   Laurentia (North America) and Baltica (Europe) collide to form Laurasia, and a volcanic island arc (Avalon terrane or Carolina terrane) collides with eastern North America.
2. Alleghanian orogeny in eastern North America and Hercynian orogeny in central Europe
   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).

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 produced the folds in the Appalachian Valley and Ridge province, and large thrust faults in the southern Appalachians. Many of these folds are asymmetrically overturned to the northwest, and the surfaces of the thrust faults are inclined southeastward.

Fold and thrust fault in the Pennsylvanian Crab Orchard Mountain Group, formed during the Alleghenian Orogeny. Note the overturned fold and southeast-dipping thrust fault. Road cut near Ozone, Tennessee, Route 40/75 eastbound. Photo courtesy of Pamela Gore.

Deep seismic reflection profiling studies indicate that the crystalline rocks of the Blue Ridge and Piedmont regions were thrust-faulted onto the craton by the continental collision, sliding at least 260 km to the west. The Blue Ridge and Piedmont metamorphic and igneous rocks form a sheet ranging from 6 to 15 km thick, overlying relatively flat-lying lower Paleozoic sedimentary rocks. This type of tectonic deformation is called "thin-skinned tectonics."

Cross-section through the southern Appalachians, based on deep seismic reflection profiles. Thickness of section on left (NW) edge is 10 km.

Orogenies in Western North America

In the western part of North America, the Antler orogeny began in the Devonian with the subduction of oceanic lithosphere beneath the western margin of the continent.

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.

The Antler Orogeny continued into the Mississippian and Pennsylvanian.