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公告 |
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Paleogeography
junshan02 发表于 2012/8/1 14:36:00 |
Finally, the Late Devonian starts with the Frasnian, ± 2.8 to ± 2.5, during which the first forests were taking shape on land. The first tetrapods appear in the fossil record in the ensuing Famennian subdivision, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, ± 2.5 million years ago.The Devonian Moncler
Down Coats Men was a relatively warm period, and probably lacked any glaciers. Reconstruction of tropical sea surface temperature from implies an average value of 30 °C (86 °F) in the Early Devonian. CO2 levels dropped steeply throughout the Devonian period as the burial of the newly-evolved forests drew carbon out of the atmosphere into sediments; this may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to Late Devonian warming. The climate would have affected the dominant organisms in Climate; would have been the main reef-forming organisms in warm periods, with corals and sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids.
The Devonian period was a time of great activity, as and drew closer together.The continent (or Laurussia) was created in the early Devonian by the collision of and , which rotated into the natural dry zone along the , which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the and the . In these near-deserts, the sedimentary beds formed, made red by the oxidized iron () characteristic of drought conditions.Near the Moncler Jackets, the of Euramerica and Gondwana were starting to meet, beginning the early stages of assembling . This activity further raised the northern and formed the in and .The west coast of Devonian North America, by contrast, was a passive margin with deep silty embayments, river deltas and estuaries, in today's and ; an approaching volcanic reached the steep slope of the continental shelf in Late Devonian times and began to uplift deep water deposits, a collision that was the prelude to the mountain-building episode of Mississippian times called the .Sea levels were high worldwide, and much of the land lay submerged under shallow seas, where tropical organisms lived. The deep, enormous (the "universal ocean") covered the rest of the . Other minor oceans were , , , and (which was closed during the collision with and Baltica). |
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