The Paleontology of North America

the Permian - 290 to 248 Million Years Ago

World Paleogeography: Around the world, the continental collisions begun in the Carboniferous continued into the Permian. These collisions assembled western Pangea and surrounded it with subduction zones. Eastern Pangea would not form until the Triassic, but the terranes that would comprise it were moving and assembling in the Paleo-Tethys Ocean. These small landmasses included the Cathaysian terranes (North China, South China, and other pieces of Southeast Asia) and the Cimmerian terranes, or Cimmeria (Turkey, Iran, Tibet, and other pieces of Central Asia). The formation of Pangea closed smaller seas between continents and uplifted mountain ranges around the supercontinent. Computer models of climate during the Permian indicate that these conditions, coupled with a large continental interior, generated a dry climate with great seasonal fluctuations. North American Paleogeography: As Pangea was assembled, most of North America was being uplifted during the Permian. This uplift generated the famous fold belts of the Appalachian Mountains and exposed more land in present-day central North America. Shallow seas covered much of modern western North America. Large reef complexes developed and extensive evaporite deposits formed in restricted lagoons at the shoreline. Farther west, subduction began, generating volcanic activity in the region of the modern Sierra Nevada. Paleontology: The Permian Period marks the end of the Paleozoic Era and the time of the largest mass extinction in Earth’s history. This extinction event affected many different environments, but it affected marine communities the most by far. It has been estimated that nearly 90% of all species became extinct at the end of the Permian. Gone were the trilobites, rugose and tabulate corals, and many species of brachiopods, molluscs, and echinoderms. As the climate became drier, the vast swamps of the Carboniferous disappeared and were replaced by forests more tolerant of dry conditions. Modern conifers first appeared in the fossil record of the Permian.

North America Today

Geologic activity over the last 250 million years has removed or covered up many of the Permian deposits around North America. While Permian rocks may be found below the surface in some states, exposures can be found in the Cascade Mountains, Sierra Nevada, Great Basin, around the Grand Canyon, from Texas to Kansas, and Ohio.

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