Miocene epoch
Miocene epoch
| Noun | 1. |  Miocene epoch - from 25 million to 13 million years ago; appearance of grazing mammals |
| 单词 | miocene epoch | |||
| 释义 | Miocene epochMiocene epoch
Miocene epochSee also: Geologic Timescale (table)Geologic Timescale Miocene epoch(mī`əsēn), fourth 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 era of geologic time (see Geologic TimescaleGeologic Timescale Era Period Epoch Approximate duration (millions of years) Approximate number of years ago (millions of years) Cenozoic Quaternary Holocene 10,000 years ago to the present Pleistocene 2 . ..... Click the link for more information. , table), lasting from around 24.6 to 5.1 million years ago. North America was more extensively submerged in the Miocene than in the preceding Oligocene epochOligocene epoch On the Pacific coast, the Great Valley of California was submerged at the beginning of the Miocene. The deposition of the Vaqueros sandstone, clay, and conglomerate was followed by the formation of the oil-rich Monterey series, partly sandstone and shale but largely diatomaceous tufa. In mid-Miocene time there was extensive mountain building in this region; the Cascades and Coast Ranges were elevating, although the Rocky Mts. had by then eroded to low relief. This disturbance was accompanied by volcanic activity—the Columbia and Snake river plateaus consist of over 200,000 sq mi (520,000 sq km) of basaltic lava flows up to 10,000 ft (3,000 m) thick—and by the first known movement along the San Andreas fault zone, engendered by the collision of the North American continental plate with the Pacific Ocean plate (see plate tectonicsplate tectonics, Late in the Miocene a new, extensive submergence resulted in the deposition of the San Pablo shale and sandstone. The sediments of the California Miocene came chiefly from the Sierra Nevada and the Klamaths, which, through erosion, were peneplained by the close of the epoch. In the western interior of North America the Columbia River basalt plateau of Idaho, Washington, Oregon, N California, and N Nevada was formed by a great outpouring of lava, which continued in the succeeding Pliocene epoch. During the Miocene most of N Europe was elevated, but marine waters covered E Spain, S France, Italy, and a depressed area extending through Hungary to a basin around Vienna. In addition to considerable mountain making, lagoons were formed at the base of the Carpathians and north of the Caucasus in the regions now occupied by the Romanian and Baku oil fields. The mammalian life of the Miocene was marked by further stages in the development of the horse, by the multiplication and final extinction of the giant hogs, and by the appearance of the mastodons, raccoons, and weasels. Cats, camels, doglike carnivores, and rhinoceroses were common, and species of a great ape (Dryopithecus) inhabited S Europe, Asia, and Africa. In the Miocene a distinct cooling of the climate resulted in the reduction of forests and an increase in grassy plains. Miocene epochMiocene epocha division of the TERTIARY PERIOD, lasting from 26 million years ago until 7 million years ago. In this epoch mammals acquired their present form. The European flora became more temperate, grasslands increased and the British Isles reached more or less the present latitude of 54 °N.Miocene epoch
Synonyms for Miocene epoch
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