Paleogene

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Paleogene
66.0 – 23.03 Ma
K-Pg extinction event.
Lower boundary GSSPEl Kef Section, El Kef, Tunisia
36°09′13″N 8°38′55″E / 36.1537°N 8.6486°E / 36.1537; 8.6486
Lower GSSP ratified1991[3]
Upper boundary definition
Upper boundary GSSPLemme-Carrosio Section,
ppm

(2 times pre-industrial)
Mean surface temperaturec. 18 °C
(4 °C above modern)

The Paleogene Period (

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.[5] Paleogene is often abbreviated "Pg", although the United States Geological Survey uses the abbreviation "Pe" for the Paleogene on the Survey's geologic maps.[6][7]

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.[8]

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.

Climate

The global climate of the Palaeogene began with the brief but intense "

Middle Palaeocene and the beginning of an intense supergreenhouse effect.[9]

From about 56 to 48 Mya, annual air temperatures over land and at mid-latitude averaged about 23–29 °C (± 4.7 °C), which is 5–10 °C warmer than most previous estimates.[13][14][15] For comparison, this was 10 to 15 °C greater than the current annual mean temperatures in these areas.[15] At the Palaeocene-Eocene boundary occurred the Paleocene–Eocene Thermal Maximum (PETM),[16] one of the warmest times of the Phanerozoic eon, during which global mean surface temperatures increased to 31.6.[17] It was followed by the less severe Eocene Thermal Maximum 2 (ETM2) about 53.69 Ma.[18] Eocene Thermal Maximum 3 (ETM3) occurred about 53 Ma. The Early Eocene Climatic Optimum was brought to an end by the Azolla event, a change of climate about 48.5 Mya, believed to have been caused by a proliferation of aquatic ferns from the genus Azolla, resulting in the sequestering of large amounts of carbon dioxide by those plants. From this time until about 34 Mya, there was a slow cooling trend known as the Middle-Late Eocene Cooling (MLEC).[9] Approximately 41.5 Ma, this cooling was interrupted temporarily by the Middle Eocene Climatic Optimum (MECO).[19] Then, about 39.4 Mya, a temperature decrease termed the Late Eocene Cool Event (LECE) is detected in the oxygen isotope record.[9] A rapid decrease of global temperatures and formation of continental glaciers on Antarctica marked the end of the Eocene.[20] This sudden cooling was caused partly by the formation of the Antarctic Circumpolar Current,[21] which significantly lowered oceanic water temperatures.[22]

During the earliest Oligocene occurred the Early Oligocene Glacial Maximum (Oi1), which lasted for about 200 thousand years.[23] After Oi1, global mean surface temperature continued to decrease gradually during the Rupelian Age. [9] Another major cooling event occurred at the end of the Rupelian; its most likely cause was extreme biological productivity in the Southern Ocean fostered by tectonic reorganisation of ocean currents and an influx of nutrients from Antarctica.[24] In the Late Oligocene, global temperatures began to warm slightly, though they continued to be significantly lower than during the previous epochs of the Palaeogene and polar ice remained.[9]

Palaeogeography

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 at 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 Myear 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.[25]

Flora and fauna

Tropical taxa diversified faster than those at higher latitudes after the Cretaceous–Paleogene extinction event, resulting in 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 period.[27] This evidence for this floral shift is found in the palynological record.[28]

See also

References

  1. .
  2. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  3. .
  4. .
  5. ^ "GeoWhen Database – What Happened to the Tertiary?". www.stratigraphy.org.
  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 23 September 2023.
  10. . Retrieved 30 December 2022.
  11. .
  12. . Retrieved 30 December 2022.
  13. .
  14. ^ University of Bristol (30 July 2018). "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". ScienceDaily.
  15. ^ a b "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". University of Bristol. 2018.
  16. S2CID 7069772
    . Retrieved 23 September 2023.
  17. . Retrieved 23 September 2023.
  18. .
  19. . Retrieved 23 September 2023.
  20. . Retrieved 23 September 2023.
  21. .
  22. . Retrieved 23 September 2023.
  23. . Retrieved 23 September 2023.
  24. .
  25. . Retrieved 24 November 2022.
  26. .
  27. .
  28. .

External links