Oligocene

EtymologyName formalityFormalName ratified1978Usage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitEpochStratigraphic unitSeriesTime span formalityFormalLower boundary definition of Planktonic ForaminifersHantkenina and Lower boundary GSSPMassignano quarry section, Massignano, Ancona, Italy
43°31′58″N13°36′04″E / 43.5328°N 13.6011°E / 43.5328; 13.6011Lower GSSP ratified1992Upper boundary definition

• Base of magnetic polarity chronozone C6Cn.2n.
• FAD of the Planktonic Foraminiferan

Upper boundary GSSPLemme-Carrosio Section, Carrosio, Italy
44°39′32″N8°50′11″E / 44.6589°N 8.8364°E / 44.6589; 8.8364Upper GSSP ratified1996

The Oligocene is a geologic epoch of the PaleogenePeriod that extends from about 33.9 million to 23 million years before the present (33.9±0.1 to 23.04±0.05 Ma). As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich from his studies of marine beds in Belgium and Germany. The name comes from Ancient Greek (olígos), lit.'few', and (kainós), lit.'new', and refers to the sparsity of extant forms of molluscs. The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.

The 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. Major changes during the Oligocene included a global expansion of grasslands, and a regression of tropical broad leaf forests to the equatorial belt.

The start of the Oligocene is marked by a notable extinction event called the Grande Coupure; it featured the replacement of European fauna with Asianfauna, except for the endemic rodent and marsupial families. By contrast, the Oligocene–Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer late Oligocene and the relatively cooler Miocene.