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Mi·o·cene (mī'ə-sēn')  |
[Greek meiōn, less + -CENE.]
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The second subdivision of the Tertiary Period (Eocene, Miocene, and Pliocene) by Charles Lyell in 1833; the fourth in a more modern sevenfold subdivision (epochs) of the Cenozoic Era; and the first epoch of the Neogene Period (which includes in successive order the Miocene, Pliocene, Pleistocene, and Holocene). The Miocene represents the interval of time from the end of the Oligocene to the beginning of the Pliocene and the rocks (series) formed during this epoch. See also Cenozoic; Holocene; Oligocene; Pleistocene; Pliocene.
The Miocene spans the time interval between 23.8 and 5.32 million years ago (Ma) based on integrated astronomical and radioisotopic dating. The Miocene/Pliocene boundary is located in Sicily, just above a major unconformity separating the youngest late Miocene (Messinian) deposits (of the Great Terminal Miocene Salinity Crisis) and the overlying white chalks of the Zanclean. See also Unconformity.
Major orogenic and volcanic events characterize the Miocene. Plate-tectonic motions, originating in the Mesozoic, resulted in the gradual dismemberment of the Tethyan Ocean and the upthrusting of the Alpine-Himalayan orogenic belt in three major phases: the late Eocene (about 40 Ma) and the early (21–17 Ma) and mid-late Miocene (10–7 Ma). Along the eastern margins of the Pacific Ocean, the ocean crust was subducted under the North and South American continents, giving rise to major orogenic movements stretching from the Aleutians to Tierra del Fuego. The Andes range was thrust up during the later part of the Miocene. The Pacific Coast developed as a result of westward drift of North America over, and partial consumption by, the Farallon plate and collision with the Farallon Ridge. Only two relatively minor plates remain as remnants of the Farallon plate: the Juan de Fuca and Cocos plates between Mexico and Alaska. The plate margin was bounded by transform faults rather than a subduction zone, and northwestern propagation of a major transform fault issuing from the Cocos plate formed the Gulf of California in the late Miocene, and its continued extension northward is familiar to residents of the west coast as the San Andreas Fault System. The latter was responsible for the formation of many of the off- and onshore basins of southern California, some of which contain prolific petroleum resources. Subduction of the Pacific plate at the Middle America Trench during the late Paleogene and Neogene resulted in arc magmatism and eventual uplift of the Central American Isthmus into a series of archipelagos in the late Miocene (about 7 Ma) and eventual fusion into a continuous land bridge in the early Pliocene (about 3 Ma) that resulted in the separation of the Atlantic and Pacific oceans and concomitant disruption in marine faunal communities as well as transcontinental migration of vertebrate animals in the Great American Faunal Interchange. See also Orogeny; Plate tectonics; Subduction zones; Transform fault.
Ocean circulation essentially assumed its modern form during the Miocene as enhanced refrigeration in the form of growth of the Antarctic Ice Sheet plunged the Earth inexorably deeper into an icehouse state, although there were some details that were completed during the succeeding Pliocene and Pleistocene epochs. An ice cap has been present on Antarctica, at least intermittently, since at least the early Oligocene (about 34 Ma). The opening of the Drake Passage between South America and Antarctica took place during the latest Oligocene–early Miocene (about 25–23 Ma), allowing the unhindered circulation of ocean currents around the Antarctic continent. The development of the Circum-Antarctic Current thermally isolated high southern latitude waters and the continent of Antarctica from the warmer, low-latitude waters and resulted in the replacement of calcareous oozes (comprising planktonic foraminifera and calcareous nannoplankton) by biosiliceous oozes (diatoms and radiolarians). See also Glacial epoch.
During the Miocene, life assumed much of its modern aspect. The spread of grasses and weeds throughout this epoch, but particularly in the late Miocene, and concomitant reduction in and thinning of forests reflected the global Neogene cooling as the Earth entered deeper into an ice house state. In this environment, snakes, frogs, and murids (rats, mice) expanded in diversity and habitat; songbirds reflect the expansion of seed-bearing herbs and, like frogs, the concomitant diversification of insects, many of which are found entombed in middle Miocene amber from the Dominican Republic. Grazing animals (elephants, rodents, horses, camelids, and rhinos, for example) developed high crowned teeth to resist significant wear caused by silicon fragments in the developing grasses. Some animals assumed gigantic proportions such as Baluchitherium, a Eurasian rhino that stood 16 ft (5 m) at the shoulders, and the tallest camel known, a giraffelike form that was over 12 ft (3.5 m) tall.
The relatively free interchange between Eurasia and Africa between 18 and 12 Ma appears to have come to an end in the late Miocene, after which (about 8 Ma) the hominoids of Eurasia and Africa appear to have followed separate and independent lines of evolution: the pongids in Asia, and the panids and hominoids leading eventually to the true hominids in (predominantly East) Africa. This scenario has been linked, in turn, with the development of the East African Rift (and its northward extension into the Red Sea and Gulf of Suez), which would have served as a geographic barrier allowing independent evolution toward forest (panid) and savannah (hominid) adapted forms. With the late Miocene change in climate (7–5 Ma) to cooler, drier conditions and the spread of open savannah and grasslands, monkeys came to dominate the African forest at the expense of dryomorphs. There is a gap in the terrestrial fossil record during this interval of time, and it is only in the early Pliocene (about 4 Ma) that the story of human evolution resumes with the discovery of the earliest true hominids (australopithecines) in East Africa, about 1 million years older than the australopithecine footprints of Laeotili and the skeletons of Lucy and other australopithecines at Hadar in Ethiopia at about 3 million years. See also Australopithecine; Fossil humans.
In the marine realm, major radiation of mammals including walruses, seals, sea lions, and whales occurred during the early Miocene. On the sea floor, large bivalve mollusks of the scallop family thrived in the early Miocene, and a distinct horizon of large pectenids occurs in lower Miocene rocks of Europe and North America and in corresponding levels in the deposits of the Paratethyan Sea in east-central Europe and at least as far to the east as Iran, attesting to an interval of global climatic amelioration. Among the protozoa, planktonic foraminifera experienced a major radiation in the early and middle Miocene following the drastic reduction in diversity during the middle and late Eocene, some 15–20 million years earlier. Mangroves and coral reefs flourished in a circumequatorial belt spanning the Indo-Pacific and Caribbean regions, but the latter were eliminated from the Mediterranean during the terminal Miocene Salinity Crisis, never to return with early Pliocene flushing from the Atlantic. See also Foraminiferida; Mangrove; Mollusca; Reef.
| Archaeology Dictionary: Miocene |
| WordNet: Miocene |
The noun has one meaning:
Meaning #1:
from 13 million to 25 million years ago; appearance of grazing mammals
Synonym: Miocene epoch
| Wikipedia: Miocene |
| System | Series | Stage | Age (Ma) | |
|---|---|---|---|---|
| Quaternary | Pleistocene | Gelasian | younger | |
| Neogene | Pliocene | Piacenzian | 2.588–3.600 | |
| Zanclean | 3.600–5.332 | |||
| Miocene | Messinian | 5.332–7.246 | ||
| Tortonian | 7.246–11.608 | |||
| Serravallian | 11.608–13.65 | |||
| Langhian | 13.65–15.97 | |||
| Burdigalian | 15.97–20.43 | |||
| Aquitanian | 20.43–23.03 | |||
| Paleogene | Oligocene | Chattian | older | |
| Subdivision of the Neogene period according to the IUGS, as of July 2009. | ||||
The Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present (23.03 to 5.33 Ma). The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words μείων (meiōn, “less”) and καινός (kainos, “new”) and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene Epoch and is followed by the Pliocene Epoch. The Miocene is the first epoch of the Neogene Period.
The earth went from the Oligocene epoch through the Miocene and into the Pliocene as it cooled into a series of Ice Ages. The Miocene boundaries are not marked by a single distinct global event but consist rather of regional boundaries between the warmer Oligocene and the cooler Pliocene.
The plants and animals of the Miocene were fairly modern. Mammals and birds were well-established. Whales, seals, and kelp spread.
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The Miocene faunal stages from youngest to oldest are typically named according to the International Commission on Stratigraphy:[1]
| Messinian | (7.246 – 5.332 Ma) |
| Tortonian | (11.608 – 7.246 Ma) |
| Serravallian | (13.65 – 11.608 Ma) |
| Langhian | (15.97 – 13.65 Ma) |
| Burdigalian | (20.43 – 15.97 Ma) |
| Aquitanian | (23.03 – 20.43 Ma) |
These subdivisions within the Miocene are defined by the relative abundance of different species of calcareous nanofossils (calcite platelets shed by brown single-celled algae) and foraminifera (single-celled protists with diagnostic shells). Two subdivisions each form the Early, Middle and Late Miocene.
Regionally, other systems are used. These ages often extend across the ICS epoch boundary into the Pliocene and Oligocene:
Australian Miocene ages are very finely divided in the early Middle Miocene, while most of the rest of the Miocene had a rather constant fauna as far as is known:[1]
| Mitchellian | (10.5 – 5 Ma); extends into the Early Pliocene |
| Bairnsdalian | (15 – 10.5 Ma) |
| Balcombian | (15.5 – 15 Ma) |
| Batesfordian | (16.5 – 15.5 Ma) |
| Longfordian | (27.5 – 16.5 Ma); includes much of the Late Oligocene |
Californian sites provide a sequence distinct from the main North American one:[1]
| Delmontian | (7.5 – 2.9 Ma); includes much of the Pliocene |
| Mohnian | (13.5 – 7.5 Ma) |
| Luisian | (15.5 – 13.5 Ma) |
| Relizian | (16.5 – 15.5 Ma) |
| Saucesian | (22 – 16.5 Ma) |
| Zemorrian | (33.5 – 22 Ma); includes nearly all the Oligocene |
Japanese Miocene ages only start in the mid-Burdigalian; the ICS ages are used in much of the Early Miocene:[1]
| Yuian | (9.5 – 3.6 Ma); includes the Early Pliocene |
| Fujian | (11.1 – 9.5 Ma) |
| Kaburan | (13.5 – 11.1 Ma) |
| Tozawan | (15.97 – 13.5 Ma) |
| Haranoyan | (18.2 – 15.97 Ma) |
In New Zealand, the following ages are recognized:[1]
| Kapitean | (6 – 4.8 Ma); extends into the Early Pliocene |
| Tongaporutuan | (10 – 6 Ma) |
| Waiauan | (11.5 – 10 Ma) |
| Lillburnian | (15 – 11.5 Ma) |
| Cliffdenian | (16.5 – 15 Ma) |
| Altonian | (17.5 – 16.5 Ma) |
| Awamoan | (20 – 17.5 Ma) |
| Hutchinsonian | (21 – 20 Ma) |
| Otaian | (23.03 – 21 Ma) |
In most of North America, faunal stages are defined according to the land mammal fauna (North American Land Mammal Ages or NALMAs):[1]
| Hemphillian | (9 – 4.75 Ma); includes much of the Early Pliocene |
| Clarendonian | (11.8 – 9 Ma) |
| Barstovian | (15.5 – 11.8 Ma) |
| Hemingfordian | (19 – 15.5 Ma) |
| Arikareean | (30.5 – 19 Ma); includes much of the Oligocene |
In South America, a system similar to the North American one is used; its periods are correspondingly called SALMAs (South American Land Mammal Ages):[2]
| Huayquerian | (9 – 5.4 Ma); the Montehermosan barely extends into the Miocene |
| Chasicoan | (10 – 9 Ma) |
| Mayoian | (12 – 10 Ma) |
| Laventan | (13.8 – 12 Ma) |
| Colloncurian | (15.5 – 12 Ma) |
| Friasian | (16.3 – 15.5 Ma) |
| Santacrucian | (17.5 – 16.3 Ma) |
| Colhuehuapian | (21 – 17.5 Ma) |
| Deseadan | (29 – 21 Ma); includes much of the Oligocene |
Continents continued to drift toward their present positions. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean, causing both the rise of the Andes and a southward extension of the Meso-American peninsula.
Mountain building took place in Western North America, Europe, and east Asia. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the American Great Plains and in Argentina.
India continued to collide with Asia, creating dramatic new mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish-Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis) near the end of the Miocene.
The global trend was towards increasing aridity caused primarily by global cooling reducing the ability of the atmosphere to absorb moisture. Uplift of East Africa in the Late Miocene was partly responsible for the shrinking of tropical rain forests in that region, and Australia got drier as it entered a zone of low rainfall in the Late Miocene.
Grasslands underwent a major expansion; forests fell victim to a generally cooler and drier climate overall. Grasses also diversified greatly, co-evolving with large herbivores and grazers, including ruminants. Between 7 and 6 million years ago, there occurred a sudden expansion of grasses which were able to assimilate carbon dioxide more efficiently but were also richer in silica, causing a worldwide extinction of large herbivores[3]. The expansion of grasslands and radiations among terrestrial herbivores such as horses can be linked to fluctuations in CO2.[4].
Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist. In the Early Miocene, several Oligocene groups were still diverse, including nimravids, entelodonts, and three-toed horses. Like in the previous Oligocene epoch, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with recognizable dogs, raccoons, horses, beaver, deer, camels, and whales, along with now extinct groups like borophagine dogs, gomphotheres, three-toed horses, and semi-aquatic and hornless rhinos like Teleoceras and Aphelops. Islands began to form between South and North America in the Late Miocene, allowing ground sloths like Thinobadistes to island-hop to North America.
Unequivocally recognizable dabbling ducks, plovers, typical owls, cockatoos and crows appear during the Miocene. By the epoch's end, all or almost all modern bird families are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved instead of too equivocal in character. Marine birds reached their highest diversity ever in the course of this epoch.
Brown algae, called kelp, proliferate, supporting new species of sea life, including otters, fish and various invertebrates. The cetaceans diversified, and some modern genera appeared, such as the sperm whales. The pinnipeds, which appeared near the end of the Oligocene, became more aquatic.
Approximately 100 species of apes lived during this time. They occupied much of the Old World and ranged in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived from between 15 to 12 million years ago.
In the oceans, modern sharks appeared at this time including the huge Megalodon. Marine crocodiles and birds, like the plotopterids and Gavialosuchus, shared the seas with marine mammals like desmostylians, dugongs like Metaxytherium, and whales, which ranged from forms similar to the ones present today to the cetotheres and the long-beaked dolphin Pomatodelphis.
There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene. Further marked decreases in temperature during the Middle Miocene at 15 Ma probably reflect increased ice growth in Antarctica. It can therefore be assumed that East Antarctica had some glaciers during the early to mid Miocene (23 – 15 Ma). Oceans cooled partly due the formation of the Antarctic Circumpolar Current, and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form. The Greenland ice cap developed later, in the Middle Pliocene time, about 3 million years ago.
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| Neogene period | |||
|---|---|---|---|
| Miocene | Pliocene | ||
| Aquitanian | Burdigalian Langhian | Serravallian Tortonian | Messinian |
Zanclean | Piacenzian | ||
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| Arikareean (geology) |
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