Paleogene

Not to be confused with Paleocene.

The Paleogene (/ˈpeɪli.ədʒiːn, -li.oʊ-, ˈpæli-/ PAL-ee-ə-jeen, -⁠ee-oh-, PAY-lee-; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) 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 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 recognised as a formal stratigraphic term, 'Tertiary' is still widely found in earth science literature and 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]

Paleogene
66.0 – 23.03 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Chronology
−65 — – −60 — – −55 — – −50 — – −45 — – −40 — – −35 — – −30 — – −25 — – M Z C e n o z o i c Cretaceous P a l e o g e n e Neogene P a l e o c e n e E o c e n e O l i g o c e n e Danian Selandian Thanetian Ypresian Lutetian Bartonian Priabonian Rupelian Chattian         ← PETM ← First Antarctic permanent ice-sheets^[1] ← K-Pg mass extinction Subdivision of the Paleogene according to the ICS, as of 2021.^[2] Vertical axis scale: millions of years ago
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°09′13″N 8°38′55″E / 36.1537°N 8.6486°E / 36.1537; 8.6486
Lower GSSP ratified	1991^[3]
Upper boundary definition	Base of magnetic polarity chronozone C6Cn.2n. Near first appearance of the Planktonic foraminiferan Paragloborotalia kugleri.
Upper boundary GSSP	Lemme-Carrosio Section, Carrosio, Italy 44°39′32″N 8°50′11″E / 44.6589°N 8.8364°E / 44.6589; 8.8364
Upper GSSP ratified	1996^[4]
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, 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 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 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 Mesozoic Era and began a cooling and drying trend. Though periodically disrupted by warm periods, such as the Latest Danian Event,^[9][10][11] Paleocene–Eocene Thermal Maximum,^[12] and Eocene Thermal Maximum 2,^[13] this trend persisted until the end of the most recent 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

Mammals began a rapid diversification during this period. After the Cretaceous–Paleogene extinction event, which saw the demise of the non-avian dinosaurs, mammals began to evolve from a few small and generalized forms into most of the modern varieties we see today. Some of these mammals evolved into large forms that dominated the land, while others became capable of living in marine, specialized terrestrial, and airborne environments. Those that took to the oceans became modern cetaceans, while those that took to the trees became primates, the group to which humans belong. Birds, extant dinosaurs which were already well established by the end of the Cretaceous, also experienced adaptive radiation as they took over the skies left empty by the now extinct pterosaurs. Some flightless birds such as penguins, ratites, and terror birds also filled niches left by the extinct hesperornithes and dinosaurs.

Pronounced cooling in the Oligocene led to a massive floral shift, and many extant modern plants arose during this time. Grasses and herbs, such as Artemisia, began to proliferate, at the expense of tropical plants, which began to decline. Conifer forests developed in mountainous areas. This cooling trend continued, with major fluctuation, until the end of the Pleistocene.^[18] This evidence for this floral shift is found in the palynological record.^[19]

See also

• Cretaceous–Paleogene boundary – Geological formation between time periods

References

1. Zachos, J. C.; Kump, L. R. (2005). "Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene". Global and Planetary Change. 47 (1): 51–66. Bibcode:2005GPC....47...51Z. doi:10.1016/j.gloplacha.2005.01.001.
2. "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
3. Molina, Eustoquio; Alegret, Laia; Arenillas, Ignacio; José A. Arz; Gallala, Njoud; Hardenbol, Jan; Katharina von Salis; Steurbaut, Etienne; Vandenberghe, Noel; Dalila Zaghibib-Turki (2006). "The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, "Tertiary", Cenozoic) at El Kef, Tunisia - Original definition and revision". Episodes. 29 (4): 263–278. doi:10.18814/epiiugs/2006/v29i4/004.
4. Steininger, Fritz F.; M. P. Aubry; W. A. Berggren; M. Biolzi; A. M. Borsetti; Julie E. Cartlidge; F. Cati; R. Corfield; R. Gelati; S. Iaccarino; C. Napoleone; F. Ottner; F. Rögl; R. Roetzel; S. Spezzaferri; F. Tateo; G. Villa; D. Zevenboom (1997). "The Global Stratotype Section and Point (GSSP) for the base of the Neogene" (PDF). Episodes. 20 (1): 23–28. doi:10.18814/epiiugs/1997/v20i1/005.
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. Meredith, R. W.; Janecka, J. E.; Gatesy, J.; Ryder, O. A.; Fisher, C. A.; Teeling, E. C.; Goodbla, A.; Eizirik, E.; Simao, T. L. L.; Stadler, T.; Rabosky, D. L.; Honeycutt, R. L.; Flynn, J. J.; Ingram, C. M.; Steiner, C.; Williams, T. L.; Robinson, T. J.; Burk-Herrick, A.; Westerman, M.; Ayoub, N. A.; Springer, M. S.; Murphy, W. J. (28 October 2011). "Impacts of the Cretaceous Terrestrial Revolution and KPg Extinction on Mammal Diversification". Science. 334 (6055): 521–524. Bibcode:2011Sci...334..521M. doi:10.1126/science.1211028. PMID 21940861. S2CID 38120449.
9. Jehle, Sofie; Bornemann, André; Lägel, Anna Friederike; Deprez, Arne; Speijer, Robert P. (1 July 2019). "Paleoceanographic changes across the Latest Danian Event in the South Atlantic Ocean and planktic foraminiferal response". Palaeogeography, Palaeoclimatology, Palaeoecology. 525: 1–13. Bibcode:2019PPP...525....1J. doi:10.1016/j.palaeo.2019.03.024. S2CID 134929774. Retrieved 30 December 2022.
10. Jehle, Sofie; Bornemann, André; Deprez, Arne; Speijer, Robert P. (25 November 2015). "The Impact of the Latest Danian Event on Planktic Foraminiferal Faunas at ODP Site 1210 (Shatsky Rise, Pacific Ocean)". PLOS ONE. 10 (11): e0141644. Bibcode:2015PLoSO..1041644J. doi:10.1371/journal.pone.0141644. PMC 4659543. PMID 26606656.
11. Sprong, M.; Youssef, J. A.; Bornemann, André; Schulte, P.; Steurbaut, E.; Stassen, P.; Kouwenhoven, T. J.; Speijer, Robert P. (September 2011). "A multi-proxy record of the Latest Danian Event at Gebel Qreiya, Eastern Desert, Egypt" (PDF). Journal of Micropalaeontology. 30 (2): 167–182. doi:10.1144/0262-821X10-023. S2CID 55038043. Retrieved 30 December 2022.
12. Wing, S. L. (2005-11-11). "Transient Floral Change and Rapid Global Warming at the Paleocene-Eocene Boundary". Science. 310 (5750): 993–996. Bibcode:2005Sci...310..993W. doi:10.1126/science.1116913. ISSN 0036-8075. PMID 16284173. S2CID 7069772.
13. Stap, L.; Lourens, L.J.; Thomas, E.; Sluijs, A.; Bohaty, S.; Zachos, J.C. (2010). "High-resolution deep-sea carbon and oxygen isotope records of Eocene Thermal Maximum 2 and H2". Geology. 38 (7): 607–610. Bibcode:2010Geo....38..607S. doi:10.1130/G30777.1. hdl:1874/385773. S2CID 41123449.
14. Naafs et al. (2018). "High temperatures in the terrestrial mid-latitudes during the early Palaeogene" (PDF). Nature Geoscience. 11 (10): 766–771. Bibcode:2018NatGe..11..766N. doi:10.1038/s41561-018-0199-0. hdl:1983/82e93473-2a5d-4a6d-9ca1-da5ebf433d8b. 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. Liu, Yang; Huang, Chunju; Ogg, James G.; Algeo, Thomas J.; Kemp, David B.; Shen, Wenlong (15 September 2019). "Oscillations of global sea-level elevation during the Paleogene correspond to 1.2-Myr amplitude modulation of orbital obliquity cycles". Earth and Planetary Science Letters. 522: 65–78. Bibcode:2019E&PSL.522...65L. doi:10.1016/j.epsl.2019.06.023. S2CID 198431567. Retrieved 24 November 2022.
18. Traverse, Alfred (1988). Paleopalynology. Unwin Hyman. ISBN 978-0045610013. OCLC 17674795.
19. Muller, Jan (January 1981). "Fossil pollen records of extant angiosperms". The Botanical Review. 47 (1): 1–142. doi:10.1007/bf02860537. ISSN 0006-8101. S2CID 10574478.

External links

 

Wikisource has original works on the topic: Cenozoic#Paleogene

 

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• Paleogene Microfossils: 180+ images of Foraminifera
• Paleogene (chronostratigraphy scale)