Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.
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Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.
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The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch.
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The Oligocene is the third and final epoch of the Paleogene Period.
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Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene.
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Major changes during the Oligocene included a global expansion of grasslands, and a regression of tropical broad leaf forests to the equatorial belt.
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Lower boundary of the Oligocene is placed at the last appearance of the foraminiferan genus Hantkenina in a quarry at Massignano, Italy.
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Upper boundary of the Oligocene is defined by its GSSP at Carrosio, Italy, which coincides with the first appearance of the foraminiferan Paragloborotalia kugleri and with the base of magnetic polarity chronozone C6Cn.
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However, towards the end of the Oligocene, there was a brief marine incursion in Europe.
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Climate during the Oligocene reflected a general cooling trend following the Early Eocene Climatic Optimum.
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Evidence of a relatively warm Oligocene suggests an enigmatic climate state, neither hothouse nor icehouse.
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The late Oligocene warming is discernible in pollen counts from the Tibetan Plateau, which show that the south Asian monsoon had already developed by the late Oligocene.
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The cooling trend that began in the middle Eocene continued into the Oligocene, bringing the poles well below freezing for the first time in the Phanerozoic.
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Oi1 event of the Eocene-Oligocene transition covered the continent of Antarctica with ice sheets, leaving Nothofagus and mosses and ferns clinging to life around the periphery of Antarctica in tundra conditions.
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The cooling of central North America at the Eocene-Oligocene transition resulted in a large turnover of gastropods, amphibians, and reptiles.
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The marine animals of Oligocene oceans resembled today's fauna, such as the bivalves.
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Oligocene sees the beginnings of modern ocean circulation, with tectonic shifts causing the opening and closing of ocean gateways.
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