Oligocene

Not to be confused with Oligogene.
Oligocene
33.9 – 23.03 Ma
A map of Earth as it appeared 30 million years ago during the Oligocene Epoch, Rupelian Age
Chronology
Etymology
Name formalityFormal
Name ratified1978
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitEpoch
Stratigraphic unitSeries
Time span formalityFormal
Lower boundary definitionLAD of Planktonic Foraminifers Hantkenina and Cribrohantkenina
Lower boundary GSSPMassignano quarry section, Massignano, Ancona, Italy
43°31′58″N 13°36′04″E / 43.5328°N 13.6011°E / 43.5328; 13.6011
Lower GSSP ratified1992[3]
Upper boundary definition
Upper boundary GSSPLemme-Carrosio Section, Carrosio, Italy
44°39′32″N 8°50′11″E / 44.6589°N 8.8364°E / 44.6589; 8.8364
Upper GSSP ratified1996

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.

  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.
  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.
  7. ^ Prothero 2005, p. 472.
  8. ^ "Oligocene". Online Etymology Dictionary.
  9. ^ Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999)