Published reconstructions of the pre-drift positions of North and South America have failed to take into account many geologic continuities present in the Paleozoic fold belts of southwestern United States, Mexico, Central America, and northwestern South America. The well-known Bullard "fit" terminates Mexico at about 23°N lat., but if southern Mexico and Central America are added, they overlap the Guianan shield of South America. Dietz and Holden attempted to solve this problem by postulating crustal blocks that filled the Gulf of Mexico and subsequently rotated southwestward to form part of Central America.

We propose a new reconstruction in which the Gulf of Mexico is completely closed by northern South America and where Mexico is adjacent to northern and northwestern South America. The evidence for this reconstruction is found in the similar geologic history of the Appalachian, Ouachita, Marathon, and Coahuila fold belts as well as throughout the eastern Andean Cordillera of Venezuela, Colombia, Ecuador, and Peru. We further propose that the Gulf of Mexico resulted from (1) the separation of North and South America by spreading and transform faulting, (2) the opening of a sphenochasm to produce the Mississippi embayment, and (3) great left-lateral displacements of the initially linear Paleozoic mobile belt along the Wichita, Texas, Coahuila, and other megashears.

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