Miocene The Miocene epoch is a division of Cenozoic time that was first distinguished by Charles Lyell in his famous book Principles of geology (1830) on the basis of the fossil mollusc fauna present in the rocks of the Paris Basin. As the earlier of the two divisions of the Neogene sub-period, it follows the Oligocene epoch and precedes the Pliocene. Today, Lyell's criterion of some 17 per cent of the Miocene mollusc fauna being extant is no longer applied; the Miocene is held to have begun at about 23 Ma and lasted for around 17 million years. It contains three series and six stages, based upon sections in the Mediterranean region. The marine biostratigraphy is based upon microfaunas and floras, notably planktonic foraminifera and radiolaria.

In North America the continental Miocene deposits of the western interior have been apportioned to three stages on the basis of their mammalian faunas, which locally are prolific.

The principal feature revealed in Miocene stratigraphy is a continuation of climatic cooling. By about 15 Ma a major ice cap had accumulated on the Antarctic continent and a permanent ice shelf was beginning to form around its shores. The circum-Antarctic current intensified and expanded. Glaciers made their appearance in the southern Andes. On the other side of the world the first significant ice fields were develop-ing in Alaska, and polar sea ice became permanent. In consequence, by 10 Ma world sea level began to fall.

At the end of the Oligocene the Ural sea had disappeared and the Himalayan uplift was taking place. Eurasia was more or less consolidated except that the Mediterranean–Tethyan region was still in motion; the seas became reduced in area, and by 18 Ma the Mediterranean was separated from the Indo-Pacific seas. Africa and Arabia were now in contact with Eurasia and free access between the two was available to land animals. The Mediterranean also became closed off from the Atlantic. In the late Miocene, desiccation lowered the level of the Mediterranean waters to well below that of the Atlantic and diminished their area by as much as 2000 km². The last stage of the Miocene was influenced by global environmental changes, probably sharp climatic fluctuation which regulated sea levels up and down. A eustatic rise of Atlantic sea level breached the Gibraltar barrier to flood the western Mediterranean evaporite basin.

Miocene littoral and sublittoral deposits on the western side of the Atlantic show the continuation of the transgression begun in earlier times, while the Gulf of Mexico continued to subside under a growing load of sands and silts.

Around 14 Ma there was a sharp increase in volcanic activity in many regions, especially in the Central American and Pacific regions. The Hawaiian hot-spot was notably active, producing basaltic flows and ashes in the islands.

In the oceans, the foraminifera were flourishing as earlier in the Cenozoic, and underwent a successful radiation to reach a peak of species diversity around 15 Ma. Thereafter they went into decline. The calcareous nannofossils, too, steadily declined in diversity until at the end of the Early Miocene only about 35 species are known. They made a short and slight comeback in the Middle Miocene.

The land flora was susceptible to minor fluctuations in temperature, and the cooling episodes were felt even in the tropics. Coniferous forests spread across the high northern latitudes, and grasslands spread in the lower latitudes. Several modern plant families made their first appearance.

In the history of the mammals the Miocene is important for the diversification of the primates around 21 Ma and the emergence of the early hominid Ramapithecus some 7 Ma later. It was around 14 Ma that many land mammals of their kind that had been common in the earlier Cenozoic were lost and new grazing types became abundant. As the climate became cooler, grasses spread and provided habitats for new grazing animals. Towards the end of the Miocene, modern cats and the first elephants arrived on the scene.

D. L. Dineley

Miocene epoch , fourth epoch of the Tertiary period in the Cenozoic era of geologic time (see Geologic Timescale , 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 epoch and underwent considerable crustal disturbances. The Atlantic and Gulf coasts were flooded about as extensively as in the Eocene epoch . Miocene rocks are found along the Atlantic as far N as Martha's Vineyard, but the series, everywhere thin, is thickest and least interrupted from New Jersey to Maryland. On the Gulf coast it extends from Florida westward to Texas. The Atlantic series is chiefly marls, clays, and sands, with diatomaceous earth; the Florida series, chiefly limestone (Florida having risen as an island in the late Oligocene); the Gulf series, limestone and clastic sediments.

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 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 Epoch

Notable in the development of primates and human evolution , are fossilized remains of Ardipithecus ramidus, perhaps one of the earliest identifiable ancestors of man. Fossilized remains found in Ethiopia date to approximately six million years ago, near the end of the Miocene Epoch. Importantly, the fossilized bones found provide evidence that Ardipithecus ramidus could walk upright. Anthropologists assert that the ancestral line between apes and humans diverged six to eight million years ago from a common ancestor that lived during the Miocene Epoch.

In geologic time , the Miocene Epoch occurs during the Tertiary Period (65 million years ago to 2.6 million years ago—and is also sometimes divided or referred to in terms of a Paleogene Period from 65 million years ago to 23 million years ago) and a Neogene Period (23 million years ago to 2.6 million years ago) instead of a singular Tertiary Period—of the Cenozoic Era of the Phanerozoic Eon . The Miocene Epoch is the fourth epoch in the Tertiary Period (in the alternative, the earliest epoch in the Neogene Period).

The Miocene Epoch ranges from approximately 23 million years ago (mya) to 5 mya. The Miocene Epoch was preceded by the Oligocene Epoch and was followed by the Pliocene Epoch .

The Miocene Epoch is further subdivided into (from earliest to most recent) Aquitanian (23 mya to 21 mya), Burdigalian (21 mya to 16 mya), Langhian (16 mya to 14 mya), Serravallian (14 mya to 10 mya), Tortonian (10 mya to 7 mya), and Messinian (7 mya to 5 mya) stages.

Craters dating to the end of the Oligocene Epoch and start of the Miocene Epoch can be studied in Northwest Canada and in Logancha, Russia. Smaller impact craters dating to the end of the middle of the Miocene Epoch are evident in Russia and Germany.

Other notable finds in the fossil record that date to the Miocene Epoch include evidence of the continued extensive development of grasslands initiated during the preceding Eocene and Oligocene Epochs. The grassland development offered a chance for grazing animals to become well established. Many of the modern migratory patterns date to the Miocene Epoch. The fusion of the Arabian plate to the Eurasian plate provided a land bridge from Africa to Asia allowing migration of species and mixing of genetic traits among reproductively compatible sub-species.

The paleobotanical record provides evidence that kelp forests also became well developed during the Miocene Epoch as the climate cyclically warmed and cooled, but more generally became less humid.

See also Archean; Cambrian Period; Cretaceous Period; Dating methods; Devonian Period; Evolution; Evolution, evidence of; Evolutionary mechanisms; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Miocene Epoch; Mississippian Period; Ordovician Period; Paleocene Epoch; Paleozoic Era; Pennsylvanian Period; Pleistocene Epoch; Precambrian; Proterozoic Eon; Quaternary Period; Silurian Period; Triassic Period

Miocene The fourth epoch of the Tertiary period, stretching from the end of the Oligocene, about 24 million years ago, to the start of the Pliocene, roughly 5 million years ago. It saw the radiation of several modern mammal groups, including the ruminants (deer, cattle, and antelopes), certain rodents (beavers, porcupines, and cavies) and the apes. Cooling of the climate during the Oligocene resulted in a continuing shift to deciduous hardwood species, such as oak and maple, at the expense of conifers during the Miocene.

Miocene Fourth of the five epochs of the Tertiary Period, extending from the end of the Oligocene, 23.3 Ma ago, to the beginning of the Pliocene, 5.2 Ma ago. Many mammals with a more modern appearance evolved during this epoch, including deer, pigs, and several elephant stocks. The Miocene comprises the Aquitanian, Burdigalian, Early and Late Langhian, Serravallian, Tortonian, and Messinian Ages.

Mi·o·cene / ˈmīəˌsēn/ • adj. Geol. of, relating to, or denoting the fourth epoch of the Tertiary period, between the Oligocene and Pliocene epochs. ∎  [as n.] (the Miocene) the Miocene epoch or the system of rocks deposited during it.

Miocene of, relating to, or denoting the fourth epoch of the Tertiary period, between the Oligocene and Pliocene epochs. This epoch lasted from 23.3 to 5.2 million years ago. During this time the Alps and Himalayas were being formed and there was diversification of the primates, including the first apes.

Miocene The fourth of the five epochs of the Tertiary Period, about 23–5.3 Ma ago, extending from the end of the Oligocene to the beginning of the Pliocene. Many mammals with a more modern appearance evolved during this epoch, including deer, pigs, and several elephant stocks.

Miocene The fourth of the five epochs of the Tertiary Period, extending from the end of the Oligocene, 23.3 Ma ago, to the beginning of the Pliocene, 5.2 Ma ago. Many mammals with a more modern appearance evolved during this epoch, including deer, pigs, and several elephant stocks.

Miocene Geological epoch beginning c.5 million years ago and ending c.5 million years ago. It falls in the middle of the Tertiary period, and is marked by a global increase in grasslands at the expense of forests and the development of most of the modern mammal groups.

Miocene The fourth of the 5 epochs of the Tertiary Period, about 24.6–5.1 Ma ago, extending from the end of the Oligocene to the beginning of the Pliocene.

miocene see EOCENE.

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