Orogenies

About 550 million years ago, during the Cambrian period, an orogeny occured that had possibly the greatest impact on North America’s formation. An orogeny is simply a mountain forming event. In this case, the orogeny, known as the Taconic Orogeny, shaped the lower levels of North America’s rock forever.

The Cambrian Period refers to roughly the time of 570-510 million years ago. The rocks formed during this time period are known as the Cambrian System, and the term Cambrian can also be applied to all living organisms that were living during this time. During the Cambrian Period, the supercontinent, known as Gondwanda, began to break apart. This massive geological event also included the separation of the Cambrian continents known as Baltica and Laurentia. When Laurentia separated from Gondwanda, it (slowly) collided with part of present-day South America. The collision of these two landmasses was what is known as the Teconic Orogeny.

The orogeny was also due to a subduction zone beneath the Lapetus Ocean. When the continental shelf began to sink from immense pressure caused by deposition, a convergent plate boundary formed along an island arc. Eventually, the island arc collided with the larger landmass, and formed huge mountains.  The Taconic Orogeny is said to have ended in the late Ordovician Period. After the Taconic Orogeny, it is believed that the Earth’s plates were relatively still for until about 350 million years ago, until the Acadian Orogeny.

 During the Paleozoic Period, the Acadian Orogeny occurred. The Acadian Orogeny was not as major as the Teconic Orogeny, but it certaintly had an impact on the formation of the Appalachians. This orogeny occured from about 375-250 million years ago. It is believed that it was caused by the collision of a small continent, Avalonia, with two larger continents. This collision changed the flow of the sea, and in turn, caused a 50 million year period of geologic unrest,

Following the Acadian Orogeny, there was the Alleghenian Orogeny. The Alleghenian Orogeny occured from about 300_350 million years ago. During this orogeny, the present-day Appalachian Mountains were higher than the Himilayas. This orogeny was caused by the collision of present day North America with Gondwanda, which is present day Africa. The evidence of this can still be seen today. Many of the rocks located in North Carolina’s Appalachians are very silimar (or identical) to those found on the western coast of Africa. Evidence can also be found all throughout the Appalachian Mountain range, which extends from Alabama to New Jersey.

The present day Appalachian mountains are not as tall as they were when they first formed. This is not due to tectonic plate movement, though. The shortening of these mountains can be mainly attributed to erosion. Although these orogenies did form the mountains, they are not responsible for the mountains’ present day topography.

http://www.jamestown-ri.info/acadian.htm

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2 Responses to Orogenies

  1. mattgwilt says:

    This is a good post. I’ll have to save this and use it to study come test time.

  2. wwhite2221 says:

    I think one of the most interesting parts about the Appalachian mountain forming period is the part where the island chain out in the Atlantic ocean actually shifted over to become part of the North American continent.

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