--> The Lower Mesozoic Rocks of Mexico Revisited


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The Lower Mesozoic Rocks of Mexico Revisited


Mexico is an important area of the western margin of Pangea that can be studied to understand the break-up of that supercontinent and its subsequent tectonic evolution during the early Mesozoic. This area is also relevant because Pacific waters passed through this area to join with the future Gulf of Mexico (GOM) and eventually connect with the North Atlantic Ocean. Marine Triassic rocks crop out only in three localities in western Mexico (Baja California, Sonora, and Zacatecas), but these outcrops demonstrate that marine transgression from the Pacific had started by that time. Early Jurassic rocks in Guerrero and Oaxaca States have ammonites that indicate continued transgression of the Pacific Ocean eastward through both the Guerrero Embayment (Erben, 1957) and the Portal del Balsas (López Ramos, 1974). These fossiliferous marine rocks provide important constraints that can be used to generate a series of paleogeographic maps that help define the tectonic evolution of the western GOM. Many plate tectonic models have been developed from geological and geophysical data to explain apparent large lateral displacements of pre-Paleozoic basement blocks. This paper shows that the entire area of Mexico must be considered and not just the GOM rim.