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Abstract

Successive phases of seafloor spreading may correspond in time to diastrophic events in South America and Africa. Examination of the tectonic history of South America and Africa leads to the conclusion that the two areas must have undergone, simultaneously, a similar sequence of tectonic events, although under different physical and mechanical conditions. Geologic events recorded from South America, Africa, and the South Atlantic suggest that major changes in the width of the Atlantic Ocean occurred as follows. The first major episode of continental drift took place at the end of the Precambrian during the worldwide Assyntian (Baykalian) orogeny, an event which also involved the remainder of the proto-Gondwana continent. Additional but less extensive continental drift involving the Gondwana continent took place during the Taconic (Ordovician), Acadian (Devonian), and Hercynian (Carboniferous) orogenies. These events culminated in the formation of the middle Atlantic Ocean basin by Late Triassic time. Another major episode of continental drift involving Africa and South America took place at the end of the Jurassic and the beginning of the Cretaceous during the Nevadan orogeny. This orogeny caused the final breakup of the Gondwana continent and resulted in the formation of the modern South Atlantic Ocean. Questions involving the exact width and depth of the proto-Atlantic Ocean are still matters of dispute.

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