Paleogene
The Paleogene Period (IPA: /ˈpeɪli.ədʒiːn, -li.oʊ-, ˈpæli-/ PAY-lee-ə-jeen, -lee-oh-, PAL-ee-; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the first part of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use. Paleogene is often abbreviated "Pg", although the United States Geological Survey uses the abbreviation "Pe" for the Paleogene on the Survey's geologic maps.
| Paleogene | |||||||||||||
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A map of Earth as it appeared during the Eocene epoch, c. 40 Ma. | |||||||||||||
| Chronology | |||||||||||||
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| Etymology | |||||||||||||
| Name formality | Formal | ||||||||||||
| Alternate spelling(s) | Palaeogene, Palæogene | ||||||||||||
| Usage information | |||||||||||||
| Celestial body | Earth | ||||||||||||
| Regional usage | Global (ICS) | ||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||
| Definition | |||||||||||||
| Chronological unit | Period | ||||||||||||
| Stratigraphic unit | System | ||||||||||||
| Time span formality | Formal | ||||||||||||
| Lower boundary definition | Iridium enriched layer associated with a major meteorite impact and subsequent K-Pg extinction event. | ||||||||||||
| Lower boundary GSSP | El Kef Section, El Kef, Tunisia 36.1537°N 8.6486°E | ||||||||||||
| Lower GSSP ratified | 1991 | ||||||||||||
| Upper boundary definition |
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| Upper boundary GSSP | Lemme-Carrosio Section, Carrosio, Italy 44.6589°N 8.8364°E | ||||||||||||
| Upper GSSP ratified | 1996 | ||||||||||||
| Atmospheric and climatic data | |||||||||||||
| Mean atmospheric O2 content | c. 26 vol % (130 % of modern) | ||||||||||||
| Mean atmospheric CO2 content | c. 500 ppm (2 times pre-industrial) | ||||||||||||
| Mean surface temperature | c. 18 °C (4 °C above modern) | ||||||||||||
During the Paleogene period, mammals continued to diversify from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.
This period consists of the Paleocene, Eocene, and Oligocene epochs. The end of the Paleocene (56 Mya) was marked by the Paleocene–Eocene Thermal Maximum, one of the most significant periods of global change during the Cenozoic, which changed oceanic and atmospheric circulation and resulted in the extinction of numerous deep-sea benthic foraminifera and on land, a major extinction of mammals. The term "Paleogene System" applies to the rocks deposited during the Paleogene Period.