DALZIEL, IAN W. D., Institute for Geophysics, The University of Texas at Austin, Austin, TX

ABSTRACT: The Origin of the Southern Margin of North America

There is no doubt that the southern margin of the North American craton was juxtaposed with northwestern Africa at the time of onset of sea floor spreading in the central Atlantic during the Mesozoic. Moreover, tradition has it that a similar continental configuration pertained when the Iapetus Ocean opened in the latest Precambrian to earliest Phanerozoic. However, new ideas regarding the configuration of the continents in the late Precambrian require reconsideration of the origin of the ancestral Gulf of Mexico continental margin.

There is evidence that the late Precambrian Cordilleran margin of North America may have rifted from the Pacific margin of the East Antarctic-Australian craton (E.M. Moores, Geology, May 1991; I. W. D. Dalziel, Geology, June 1991 and Ann. Revs. Earth and Planetary Sci., 1992). A case can also be made that the Appalachian margin was juxtaposed with the proto-Andean margin of South America (I. W. D. Dalziel, GSA Today, November, 1992).

The occurrence of a Cambro-Ordovician platform carbonate succession with North American "Pacific realm" trilobites in NW Argentina, and the presence of carbonates of the same age with trilobites of Argentine-Bolivianaffinities in the Oaxaca block of southern Mexico, have been recognized for some time. They provide independent proto-Andean margins prior to the opening of the Pacific Ocean basin and the amalgamation of Gondwana.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.