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| This epoch is part of the Tertiary period and the Paleogene subperiod. |
| Pliocene |
| Miocene |
| Oligocene |
| Eocene |
| Paleocene |
The Oligocene epoch is a geologic period of time that extends from about 33.7 million to 23.8 million years before the present (BP). As with other older geologic periods, the rock beds that define the period are well identified, but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene refers to the sparsity of additional modern mammalian faunas after a burst of evolution during the Eocene. The Oligocene follows the Eocene epoch and is followed by the Miocene epoch. The Oligocene is the third epoch of the Tertiary era.
The start of the Oligocene is marked by a major extinction event that may be related to the impact of large extraterrestrial object in Siberia and/or near Chesapeake Bay. The Oligocene-Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the relatively cooler Miocene.
Oligocene faunal stages from youngest to oldest are:
Climates remained warm, although the slow global cooling that eventualty led to the Pleistocene glaciationsGlaciation often called an ice age is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. Glaciations are characterized by cool, wet climates and thick ice sheets extending south of each pol started around the end of the epoch.
see: PaleoMap Project: Oligocene
During this period, the continents continued to driftThe concept of continental drift was first proposed by Alfred Wegener. In 1912 he noticed that the shapes of continents on either side of the Atlantic Ocean seem to fit together (for example, Africa and South America). Benjamin Franklin and others had not toward their present positions.
Mountain buildingOrogeny is a geologic term associated with periods of mountain building. An orogenic belt therefore, is a geologic structure associated with continental collisions and mountain building. Generally orogenic belts consist of long parallel strips of rock exh in western North AmericaNorth America is the third largest continent in area and the fourth ranked in population. It is bounded on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and on the west by the North Pacific Ocea continued, and the AlpsThe Alps is the collective name for one of the great mountain range systems of Europe, stretching from Austria in the east, Slovenia, Italy, Switzerland, Liechtenstein and Germany, through to France in the west. The highest mountain in the Alps is the Mon started to rise in Europe as the African plate continued to push north into the Eurasian plate. A brief marine incursion marks the early Oligocene in Europe. Oligocene marine exposures are rare in North America. There appears to have been a land bridge in the early Oligocene between North America and Europe as the faunas of the two regions are very similar.