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Eocene epoch(ē`əsēn'), second epoch of the Tertiary periodTertiary period
, name for the major portion of the Cenozoic era, the most recent of the geologic eras (see Geologic Timescale, table) from around 26 to 66 million years ago. The name Tertiary was first applied about the middle of the 18th cent.
..... Click the link for more information. in the Cenozoic eraCenozoic era
, last major division of geologic time (see Geologic Timescale, table) lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the
..... Click the link for more information. of geologic time, from approximately 54.9 to 38 million years ago. The Eocene in North America was marked by the submergence of the Great Valley of California and a portion of the Atlantic and Gulf coastal plain extending from New Jersey to Texas and into the present Mississippi River valley as far north as S Illinois. There was also extensive sediment deposition in the Rocky Mt. region. Eocene sedimentary formations along the Atlantic-Gulf coast are chiefly sands, clays, and marls, with some limestone and lignite; in California, Oregon, and Washington they consist of shale and sandstone, with oil and coal. The Badlands of the West are partly cut into Eocene rock formations, e.g., the Wasatch, Green River, Bridger, and Uinta formations, which contain great quantities of volcanic ash and, in some districts, oil-producing shale. The Green River formation of SW Wyoming is noted for its freshwater fossil fish. The brightly colored Wasatch formation makes up the spectacular pillars of Bryce Canyon National Park. Interpretation of Eocene rock strata is based on the succession of beds in Belgian, French, and English basins, which became type areas. The Norwegian-Greenland Sea began to open during the Eocene, and a great inundation from the Mediterranean covered most of S Europe, N Africa, and SW Asia, depositing nummulitic limestone, which is prominent in the Alps and Carpathians and from which the stones of the Pyramids were quarried. Mammals became the dominant animals, and the ancestors of the common animals of Europe and North America made their appearance, possibly as immigrants from other regions. Eocene mammals included ancestral rhinoceroses, tapirs, camels, pigs, rodents, monkeys, whales, and the ancestral horse, eohippus, as well as animals such as the titanothere, which have since become extinct. The vegetation of the Eocene was fairly modern; the climate was warm.
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