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The Late Triassic-Late Cretaceous Flooding of the Gulf of Mexico From the Pacific Through Mexico


During the Late Triassic a major system of graben and horsts were formed as a consequence of the break-up of western Pangea, and Laurasia Plate started to drift apart from the Gondwana Plate, all along under the influence of the Farallon Plate. In the early stages of this tectonic event thick sequences of continental clastics were deposited over the Pre-Mesozoic basement, as well as local lava flows in the floor of these low relieve areas. The continuous subsidence of these grabens allowed the invasion of marine water from the Pacific developing an extensive shallow water seaway through these basins across Mexico. The basement highs remained emerged acting also as source of clastic sediments. There are different opinions about the time and location of invasion of marine water to flood the GOM, but there is also field evidence that indicate that the seaway to flood the GOM was the Portal del Balsas. One piece of evidence is the Callovian age of the extensive salt masses in the GOM which indicate that the basin was completely open by that time, and that it had a low relief and probably an east-west rise in between the Yucatan Block and the northern rim of the GOM. A second piece of evidence are the Early Mesozoic rocks in Mexico; marine Triassic rocks are located only in three states in western part of the country: Baja California, Sonora, and Zacatecas, indicating that the transgression of pacific marine water through the GOM started by that time. However, Early Jurassic marine rocks with ammonites and bivalves crop-out in Guerrero and Oaxaca States, which indicate that a younger southern transgression from the Pacific Ocean took place eastward through the Guerrero Embayment and the Portal del Balsas. A third piece of important evidence in the tectonic reconstruction of the opening of the GOM are the regional gravity maps recently published by Sandwell et al. (2014).