Overview:

Summary of Paleozoic Orogenies

Mount Katahdin

During the Ordovician, the Iapetus Ocean separating Baltica (present-day Western Europe) and Laurentia (present-day North America) began to close, causing Baltica and Laurentia to converge. Volcanic island arcs located in the Iapetus Ocean collided with the coast of Laurentia, causing the Taconic orogenesis. During the Silurian, the Taconic Mountains gradually eroded away. Avalonia, a micro-continent originating from Gondwana (Africa) moved northwards towards a collision with Laurentia. Continued convergence in the southern Iapetus Sea initiated the Caledonian orogeny, the precursor to the Acadian orogeny. The Caledonian orogeny was caused by the collision between Baltica and Greenland, which was attached to Canada at the time. Much of the deformation caused by the Caledonian orogenesis is located in present-day western Europe.

During the Devonian the Iapetus Sea was reduced to a shallow basin, Laurentia was located at the equator, and warm shallow seas covered most of present day North America. During this time Baltica (Western Europe) and Laurentia (North America) converged, causing the terranes* located in between the two continents to be deformed and metamorphosed. Terranes such as Avalonia became sutured to the East Coast of Laurentia, adding the landmass of present day New England. The collision of Avalonia and other terranes with Laurentia produced the Acadian orogenesis. The Acadian orogeny and the Caledonian orogeny mark the assemblage of the super-continent Laurussia. The erosion of the Acadian orogeny produced the Catskill Clastic Wedge, while similar deltaic sediments or molasse are called the Old Red Sandstone in Europe.

The collision of Laurussia with Gondwana, which began in the Mississippian and continued through the Permian, resulted in the Alleghanian orogeny, which overprinted much of the deformation produced during the Acadian orogeny and produced the major structures of the central and southern Appalachians. With Laurussia and Gondwana now sutured together, Pangea had been formed. This was the last major orogenic event to affect the present-day east coast of North America.

 

*Bold face words are defined in the glossary.

 

Positions of Terranes in Early Devonian