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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.
Other genera of Oligocene indricotheres, such as Baluchitherium, Indricotherium, and Pristinotherium, have been named, but no complete specimens exist, making comparison and classification difficult. Most modern scientists consider these genera to be junior synonyms of Paraceratherium , and it is thought to contain the following species; P ...
The Eocene–Oligocene extinction event, also called the Eocene-Oligocene transition (EOT) or Grande Coupure (French for "great cut"), is the transition between the end of the Eocene and the beginning of the Oligocene, an extinction event and faunal turnover occurring between 33.9 and 33.4 million years ago. [1]
The transition from the Eocene to the Oligocene is found in Chron 13, which occupies the lower part of the Gebel-Qatrani Formation. Accordingly, by far the largest part of the rock unit is of Oligocene origin, only the lowest 48 m was already formed in the Upper Eocene.
A brief marine incursion marks the early Oligocene in Europe. There appears to have been a land bridge in the early Oligocene between North America and Europe since the faunas of the two regions are very similar. During the Oligocene, South America was finally detached from Antarctica and drifted north toward North America.
The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that was a major step into the icehouse climate. [106] Multiple proxies, such as oxygen isotopes and alkenones , indicate that at the Eocene–Oligocene transition, the atmospheric carbon dioxide concentration had ...
The base of the Rupelian Stage (which is also the base of the Oligocene Series) is at the extinction of the foraminiferan genus Hantkenina. An official GSSP for the base of the Rupelian has been assigned in 1992 (Massignano, Italy). The transition with the Chattian has also been marked with a GSSP in August 2017 (Monte Conero, Italy). [5]
The volcanic clastic Ohanapecosh Formation is an early state of cascade volcanism. It has been dated to the middle Oligocene [36 to 28 Ma]. [1] The strata are as much as 3 kilometres (1.9 miles) thick, with exposures visible in more than 400 square kilometres (99,000 acres) of a total area exceeding 700 square kilometres (170,000 acres).