Appalachian Mountains Orogeny

The Appalachian mountains orogeny dates back to the beginning of the Paleozoic era, about 530 million years ago. Today, these mountains are only a fragment of what used to be a much larger orogenic system, which had a direct northern continuation in the Caledonian mountain belt of Great Britain, east Greenland, and northwestern Scandinavia. This old mountain chain of North America extends some 3,200 km, from Newfoundland to Alabama, with an exposed width which ranges from 150 to 650 km. The narrowest part is in New York.

Orogenic Periods of the Appalachians

There are four major periods in the orogeny of the Appalachian mountain system.The Avalonian, which began in the Cambrian (520 million years ago); the Taconic, at the end of the Ordovician (445 million years ago); the Acadian, at the end of the Devonian (360 million years ago); and the Carboniferous-Permian (300 millions years). The first three orogenic periods can be seen in the northern Appalachians and Newfoundland, and the last orogenic period are exposed in the southern Appalachians and it is characterized by an intermontaine sag which was filled with intercontinental coal deposits. Therefore, the southern Appalachians consist of upper Paleozoic deposits, which are linked to important deposits of coal, gas, and oil, with its external wider zone comprising folds pointing northwest and accumulation of Lower and Middle Paleozoic granite and other rocks.

The last uplift and folding the southern Appalachians took place toward the end of the Paleozoic era. In the late Triassic period (Mesozoic era), however, the structure of the Appalachians was altered by grabens, which are elongated depressions of land between two faults. These grabens were then filled with red continental deposits and basalt extrusions. The western edge of the Appalachian mountain belt is a fold-and-thrust belt that impinges on the stable North American craton (a geologically stable portion of the continental crust that has not been deformed or altered significantly for millions of years). Along the western edge of the Appalachian mountains, sedimentary rocks span virtually the entire Paleozoic era, providing an extensive indirect record of nearby mountain building.