Oligocene

Oligocene
Oligocene
	A map of Earth as it appeared 30 million years ago during the Oligocene Epoch, Rupelian Age
Chronology
←	PETM
←	First Antarctic permanent ice-sheets
←	K-Pg mass; extinction
	Subdivision of the Paleogene according to the ICS, as of 2021.; Vertical axis scale: millions of years ago;
Etymology
Name formality	Formal
Name ratified	1978
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Epoch
Stratigraphic unit	Series
Time span formality	Formal
Lower boundary definition	LAD of Planktonic Foraminifers Hantkenina and Cribrohantkenina
Lower boundary GSSP	Massignano quarry section, Massignano, Ancona, Italy; 43°31′58″N 13°36′04″E / 43.5328°N 13.6011°E
Lower GSSP ratified	1992
Upper boundary definition	Base of magnetic polarity chronozone C6Cn.2n.; FAD of the Planktonic Foraminiferan Paragloborotalia kugleri;
Upper boundary GSSP	Lemme-Carrosio Section, Carrosio, Italy; 44°39′32″N 8°50′11″E / 44.6589°N 8.8364°E
Upper GSSP ratified	1996

The Oligocene (IPA: /ˈɒlɪɡəsiːn, -ɡoʊ-/ OL-ə-gə-seen, -⁠goh-)^[4] is a geologic epoch of the Paleogene Period that extends from about 33.9 million to 23 million years before the present (33.9±0.1 to 23.03±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^[5]^[6] from his studies of marine beds in Belgium and Germany.^[7] The name comes from Ancient Greek ὀλίγος (olígos) 'few' and καινός (kainós) 'new',^[8] 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.^[9] 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 Asian fauna, 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.

^ Zachos, J. C.; Kump, L. R. (2005). "Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene". Global and Planetary Change. 47 (1): 51–66. Bibcode:2005GPC....47...51Z. doi:10.1016/j.gloplacha.2005.01.001.
^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
^ Silva, Isabella; Jenkins, D. (September 1993). "Decision on the Eocene-Oligocene boundary stratotype" (PDF). Episodes. 16 (3): 379–382. doi:10.18814/epiiugs/1993/v16i3/002. Retrieved 13 December 2020.
^ "Oligocene Definition & Meaning". Dictionary.com. Retrieved 2022-05-13.
^ Beyrich (November 1854). "Über die Stellung der hessische Tertiärbildungen" [On the position of the Hessian Tertiary formations]. Verhandlungen Köngliche Preussischen Akademie Wissenschaft Berlin [Proceedings of the Royal Prussian Academy of Sciences at Berlin]: 640–666. From p. 664: "Der neue Name Oligocän mag sich zwischenstellen zwischen das ältere Eocän und das jüngere Miocän." (The new name Oligocene may be interposed between the older Eocene and the younger Miocene.)
^ Wilmarth, Mary Grace (1925). Bulletin 769: The Geologic Time Classification of the United States Geological Survey Compared With Other Classifications, accompanied by the original definitions of era, period and epoch terms. Washington, D.C., U.S.: U.S. Government Printing Office. p. 53.
^ Prothero 2005, p. 472.
^ "Oligocene". Online Etymology Dictionary.
^ Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999)

[Zachos2k5-1] Zachos, J. C.; Kump, L. R. (2005). "Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene". Global and Planetary Change. 47 (1): 51–66. Bibcode:2005GPC....47...51Z. doi:10.1016/j.gloplacha.2005.01.001.

[2] "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.

[stratigraphy379-3] Silva, Isabella; Jenkins, D. (September 1993). "Decision on the Eocene-Oligocene boundary stratotype" (PDF). Episodes. 16 (3): 379–382. doi:10.18814/epiiugs/1993/v16i3/002. Retrieved 13 December 2020.

[4] "Oligocene Definition & Meaning". Dictionary.com. Retrieved 2022-05-13.

[5] Beyrich (November 1854). "Über die Stellung der hessische Tertiärbildungen" [On the position of the Hessian Tertiary formations]. Verhandlungen Köngliche Preussischen Akademie Wissenschaft Berlin [Proceedings of the Royal Prussian Academy of Sciences at Berlin]: 640–666. From p. 664: "Der neue Name Oligocän mag sich zwischenstellen zwischen das ältere Eocän und das jüngere Miocän." (The new name Oligocene may be interposed between the older Eocene and the younger Miocene.)

[6] Wilmarth, Mary Grace (1925). Bulletin 769: The Geologic Time Classification of the United States Geological Survey Compared With Other Classifications, accompanied by the original definitions of era, period and epoch terms. Washington, D.C., U.S.: U.S. Government Printing Office. p. 53.

[FOOTNOTEProthero2005472-7] Prothero 2005, p. 472.

[OnlineEtDict-8] "Oligocene". Online Etymology Dictionary.

[9] Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999)

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