Southwest region, Mexico |
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Paleontology and geologyThe Precambrian: Most of the Southwestern Region of Mexico did not exist in the Precambrian, except for a few areas in the east where Precambrian rocks form a basement under younger rocks and outcrop in a few places. These metamorphic and igneous rocks date back to 1.0 Ga and formed along ancient Gondwana. The movement of tectonic plates brought them to their present position in Mexico. The Paleozoic: For most of the Paleozoic, much of the Southwestern Region did not exist, except for some areas in the east. These rocks were of sedimentary and igneous origin, deposited off the coast of Gondwana, south of, and an ocean away from, Laurentia. But toward the end of the Paleozoic, the two continents collided, folding, faulting, and altering these rocks while bringing them near to their present-day position. The collision also pushed up some areas, which became covered in forests and wetlands. The western margin of the region was covered in shallow to deep seas that were home to various invertebrates and fishes. The Mesozoic: Gondwana and Laurentia rifted apart in the Mesozoic but some Gondwana rocks remained in what is now the eastern part of the Southwestern Region. To the west, subduction pushed volcanic islands and slices of oceanic crust against the newly formed continental margin. This activity brought magma near the surface, creating subsurface masses of granite and producing many volcanic eruptions. Over time, the western side of the region was pushed up while the eastern side was flooded by shallow seas. Forests and swamps covered the land, where dinosaurs, pterosaurs, and other animals lived, and the seas were filled with various invertebrates and fishes. The Cenozoic: In the Cenozoic, the Southwestern Region of Mexico was pushed up and continued to experience substantial volcanic activity. The interactions between the continental plate and oceanic plates in the west changed, which created a line of volcanoes across the northern part of the region. Occasionally, lakes would form behind lava flows, creating wave-cut terraces and leaving deposits on many hillsides. The land was covered in forests, grasslands, and chaparral, and these habitats were home to many animals from both North and South America. As the climate cooled, glaciers developed on the highest mountains. |
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