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66.0 – 23.03 Ma

The Paleogene (

Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning 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.[5] Paleogene is often abbreviated "Pg" (but the United States Geological Survey uses the abbreviation Pe for the Paleogene on the Survey's geologic maps).[6][7]

During the Paleogene, mammals diversified 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.[8]

This period consists of the

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 upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera
and on land, a major turnover in mammals. The term "Paleogene System" is applied to the rocks deposited during the Paleogene Period.

Climate and geography

The global climate during the Paleogene departed from the hot and humid conditions of the late

glacial period of the current ice age, when temperatures began to rise again. The trend was partly caused by the formation of the Antarctic Circumpolar Current, which significantly lowered oceanic water temperatures. A 2018 study estimated that during the early Palaeogene about 56-48 million years ago, annual air temperatures, over land and at mid-latitude, averaged about 23–29 °C (± 4.7 °C), which is 5–10 °C higher than most previous estimates.[14][15] For comparison, this was 10 to 15 °C higher than the current annual mean temperatures in these areas. The authors suggest that the current atmospheric carbon dioxide trajectory, if it continues, could establish these temperatures again.[16]

During the Paleogene, the continents continued to drift closer to their current positions. India was in the process of colliding with Asia, forming the Himalayas. The Atlantic Ocean continued to widen by a few centimeters each year. Africa was moving north to collide with Europe and form the Mediterranean Sea, while South America was moving closer to North America (they would later connect via the Isthmus of Panama). Inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting toward Southeast Asia. The 1.2 Myr cycle of obliquity amplitude modulation governed eustatic sea level changes on shorter timescales, with periods of low amplitude coinciding with intervals of low sea levels and vice versa.[17]

Flora and fauna

Tropical taxa diversified faster than those at higher latitudes following the Cretaceous–Paleogene extinction event, leading to the development of a significant latitudinal diversity gradient.

terror birds also filled niches left by the hesperornithes
and other extinct dinosaurs.

Pronounced cooling in the

Conifer forests developed in mountainous areas. This cooling trend continued, with major fluctuation, until the end of the Pleistocene.[19] This evidence for this floral shift is found in the palynological record.[20]

See also


  1. .
  2. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  3. .
  4. .
  5. ^ "GeoWhen Database – What Happened to the Tertiary?".
  6. ^ Federal Geographic Data Committee. "FGDC Digital Cartographic Standard for Geologic Map Symbolization" (PDF). The National Geologic Map Database. United States Geological Survey. Retrieved 29 January 2022.
  7. ^ Orndorff, R.C. (20 July 2010). "Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units" (PDF). United States Geological Survey. Retrieved 29 January 2022.
  8. S2CID 38120449
  9. . Retrieved 30 December 2022.
  10. .
  11. . Retrieved 30 December 2022.
  12. .
  13. .
  14. S2CID 135045515.{{cite journal}}: CS1 maint: uses authors parameter (link
  15. ^ University of Bristol (30 July 2018). "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". ScienceDaily.
  16. ^ "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". University of Bristol. 2018.
  17. S2CID 198431567
    . Retrieved 24 November 2022.
  18. . Retrieved 19 March 2023.
  19. .
  20. .

External links