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Topic%2015_Jurassic - JURASSIC 13-1 Jurassic Period The...

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JURASSIC 13-1 7-1 Jurassic Period The Jurassic Period is a major unit of the geologic time scale that extends from about 200 to 145 Ma, the end of the Triassic to the beginning of the Cretaceous. As with other geologic periods, the rock beds that define the start and end of the period are well identified but the exact dates are uncertain by 5 - 10 million years. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Dinosaurs". The start of the period is marked by the major Triassic-Jurassic extinction event. The Jurassic was named for the extensive marine limestone exposures of the Jura Mountains, in the region where Germany, France and Switzerland meet. Very limited outcrops of Jurassic age rocks occur in Hell’s canyon, south of Moscow. This period extends roughly from 150 to 200 million years ago. A range composed of Jurassic rocks in the Alps. Location of an outcrop of Jurassic rock in Idaho. Paleogeography During the early Jurassic, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; the Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart. The Tethys Sea closed, and the Neotethys basin appeared. Climates were warm, with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole, and no extensive ice caps existed. The Jurassic geological record is good in western Europe, where extensive marine sequences indicate a time when much of the continent was submerged under shallow tropical seas; famous locales include the Jurassic Coast World Heritage Site and the renowned late Jurassic Solnhofen fossils. In contrast, the North American Jurassic record is the poorest of the Mesozoic, with few outcrops at the surface. Though the epicontinental Sundance Sea left marine deposits in parts of the northern plains of the United States and Canada during the late Jurassic, most exposed sediments from this period are continental, such as the alluvial deposits of the Morrison Formation. The first of several massive batholiths were emplaced in the northern Cordillera beginning in the mid- Jurassic, marking the Nevadan orogeny. During this period, Pangea broke up into Gondwana and Laurasia, forming the Gulf of Mexico. A world famous Jurassic limestone for fossil vertebrates in Europe. A Jurassic marine deposit in the northern plains. A famous Jurassic alluvial formation for dinosaur bones in the western States. Fauna During the Jurassic, the primary vertebrates living in the seas were fish and marine reptiles. The latter include ichthyosaurs, plesiosaurs and marine crocodiles.
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