Paleogene

Last updated
Paleogene
66.0 – 23.03 Ma
40 Ma paleoglobe.png
A map of Earth as it appeared during the Eocene epoch, c. 40 Ma.
Chronology
Etymology
Name formalityFormal
Alternate spelling(s)Palaeogene, Palæogene
Usage information
Celestial body Earth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unit Period
Stratigraphic unit System
Time span formalityFormal
Lower boundary definition Iridium enriched layer associated with a major meteorite impact and subsequent K-Pg extinction event.
Lower boundary GSSPEl Kef Section, El Kef, Tunisia
36°09′13″N8°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, Carrosio, Italy
44°39′32″N8°50′11″E / 44.6589°N 8.8364°E / 44.6589; 8.8364
Upper GSSP ratified1996 [4]
Atmospheric and climatic data
Mean atmospheric O2 contentc. 26 vol %
(130 % of modern)
Mean atmospheric CO2 contentc. 500 ppm
(2 times pre-industrial)
Mean surface temperaturec. 18 °C
(4 °C above modern)

The Paleogene Period ( IPA: /ˈpli.ən,-li.-,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. [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]

Contents

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 "impact winter" caused by the Chicxulub impact. This cold period was terminated by an abrupt warming. After temperatures stabilised, the steady cooling and drying of the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI) that had spanned the last two stages of the Late Cretaceous continued. [9] About 62.2 Ma, the Latest Danian Event, a hyperthermal event, took place. [10] [11] [12] About 59 Ma, the LKEPCI was brought to an end by the Thanetian Thermal Event, a change from the relative cool of the Early and 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. [26] 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 presently. 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 adapted to the oceans became modern cetaceans, while those that adapted to 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 hesperornithes and other extinct dinosaurs.

Pronounced cooling in the Oligocene resulted in 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 decrease. 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

Related Research Articles

<span class="mw-page-title-main">Cretaceous</span> Third and last period of the Mesozoic Era, 145-66 million years ago

The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

<span class="mw-page-title-main">Cenozoic</span> Third era of the Phanerozoic Eon

The Cenozoic is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterised by the dominance of mammals, birds, and angiosperms. It is the latest of three geological eras, preceded by the Mesozoic and Paleozoic. The Cenozoic started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.

<span class="mw-page-title-main">Eocene</span> Second epoch of the Paleogene Period

The Eocene is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name Eocene comes from the Ancient Greek ἠώς and καινός and refers to the "dawn" of modern ('new') fauna that appeared during the epoch.

<span class="mw-page-title-main">Neogene</span> Second geologic period in the Cenozoic Era 23–2.6 million years ago

The Neogene is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 million years ago. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868). The earlier term Tertiary Period was used to define the span of time now covered by Paleogene and Neogene and, despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use.

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich from his studies of marine beds in Belgium and Germany. The name comes from the Ancient Greek ὀλίγος and καινός, and refers to the sparsity of extant forms of molluscs. The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.

The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

<span class="mw-page-title-main">Paleoclimatology</span> Study of changes in ancient climate

Paleoclimatology is the scientific study of climates predating the invention of meteorological instruments, when no direct measurement data were available. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to understand natural variation and the evolution of the current climate.

<span class="mw-page-title-main">Paleocene–Eocene Thermal Maximum</span> Global warming about 55 million years ago

The Paleocene–Eocene thermal maximum (PETM), alternatively "Eocene thermal maximum 1" (ETM1), and formerly known as the "Initial Eocene" or "Late Paleocene thermal maximum", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event occurred at the time boundary of the Paleocene and Eocene geological epochs. The exact age and duration of the event is uncertain but it is estimated to have occurred around 55.5 million years ago (Ma).

The geologic temperature record are changes in Earth's environment as determined from geologic evidence on multi-million to billion (109) year time scales. The study of past temperatures provides an important paleoenvironmental insight because it is a component of the climate and oceanography of the time.

TEX<sub>86</sub>

TEX86 is an organic paleothermometer based upon the membrane lipids of mesophilic marine Nitrososphaerota (formerly "Thaumarchaeota", "Marine Group 1 Crenarchaeota").

The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian is at the Cretaceous–Paleogene extinction event 66 Ma. The age ended 61.6 Ma, being followed by the Selandian.

The Thanetian is, in the ICS Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or Series. It spans the time between 59.2 and56 Ma. The Thanetian is preceded by the Selandian Age and followed by the Ypresian Age. The Thanetian is sometimes referred to as the Late Paleocene.

<span class="mw-page-title-main">Ypresian</span> First age of the Eocene Epoch

In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between 56 and47.8 Ma, is preceded by the Thanetian Age and is followed by the Eocene Lutetian Age. The Ypresian is consistent with the lower Eocene.

<span class="mw-page-title-main">Eocene–Oligocene extinction event</span> Mass extinction event 33.9 million years ago

The Eocene–Oligocene extinction event, also called the Eocene-Oligocene transition (EOT) or Grande Coupure, 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. It was marked by large-scale extinction and floral and faunal turnover, although it was relatively minor in comparison to the largest mass extinctions.

<span class="mw-page-title-main">Seymour Island</span> Island in Antarctica

Seymour Island or Marambio Island, is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is the closest part of Antarctica to South America. It lies within the section of the island chain that resides off the west side of the peninsula's northernmost tip. Within that section, it is separated from Snow Hill Island by Picnic Passage, and sits just east of the larger key, James Ross Island, and its smaller, neighboring island, Vega Island.

<span class="mw-page-title-main">Azolla event</span> Hypothetical geoclimatic event

The Azolla event is a paleoclimatology scenario hypothesized to have occurred in the middle Eocene epoch, around 49 million years ago, when blooms of the carbon-fixing freshwater fern Azolla are thought to have happened in the Arctic Ocean. As the fern died and sank to the stagnant sea floor, they were incorporated into the sediment over a period of about 800,000 years; the resulting draw-down of carbon dioxide has been speculated to have helped reverse the planet from the "greenhouse Earth" state of the Paleocene-Eocene Thermal Maximum, when the planet was hot enough for turtles and palm trees to prosper at the poles, to the current icehouse Earth known as the Late Cenozoic Ice Age.

The Paleocene, or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek παλαιός palaiós meaning "old" and the Eocene Epoch, translating to "the old part of the Eocene".

Eocene Thermal Maximum 2 (ETM-2), also called H-1 or the Elmo event, was a transient period of global warming that occurred around either 54.09 Ma or 53.69 Ma. It appears to be the second major hyperthermal that punctuated the long-term warming trend from the Late Paleocene through the Early Eocene.

The climate across the Cretaceous–Paleogene boundary is very important to geologic time as it marks a catastrophic global extinction event. Numerous theories have been proposed as to why this extinction event happened including an asteroid known as the Chicxulub asteroid, volcanism, or sea level changes. While the mass extinction is well documented, there is much debate about the immediate and long-term climatic and environmental changes caused by the event. The terrestrial climates at this time are poorly known, which limits the understanding of environmentally driven changes in biodiversity that occurred before the Chicxulub crater impact. Oxygen isotopes across the K–T boundary suggest that oceanic temperatures fluctuated in the Late Cretaceous and through the boundary itself. Carbon isotope measurements of benthic foraminifera at the K–T boundary suggest rapid, repeated fluctuations in oceanic productivity in the 3 million years before the final extinction, and that productivity and ocean circulation ended abruptly for at least tens of thousands of years just after the boundary, indicating devastation of terrestrial and marine ecosystems. Some researchers suggest that climate change is the main connection between the impact and the extinction. The impact perturbed the climate system with long-term effects that were much worse than the immediate, direct consequences of the impact.

A hyperthermal event corresponds to a sudden warming of the planet on a geologic time scale.

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. 1 2 3 4 5 6 Scotese, Christopher Robert; Song, Haijun; Mills, Benjamin J.W.; van der Meer, Douwe G. (April 2021). "Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years". Earth-Science Reviews . 215: 103503. Bibcode:2021ESRv..21503503S. doi:10.1016/j.earscirev.2021.103503. S2CID   233579194 . Retrieved 23 September 2023.
  10. 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.
  11. 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.
  12. 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. Bibcode:2011JMicP..30..167S. doi:10.1144/0262-821X10-023. S2CID   55038043. Archived from the original (PDF) on 28 June 2023. Retrieved 30 December 2022.
  13. Naafs, B. D. A.; Rohrssen, M.; Inglis, G. N.; Lähteenoja, O.; Feakins, S. J.; Collinson, M. E.; Kennedy, E. M.; Singh, P. K.; Singh, M. P.; Lunt, D. J.; Pancost, R. D. (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.
  14. University of Bristol (30 July 2018). "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". ScienceDaily.
  15. 1 2 "Ever-increasing CO2 levels could take us back to the tropical climate of Paleogene period". University of Bristol. 2018.
  16. Wing, S. L. (11 November 2005). "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 . Retrieved 23 September 2023.
  17. Inglis, Gordon N.; Bragg, Fran; Burls, Natalie J.; Cramwinckel, Margot J.; Evans, David; Foster, Gavin L.; Huber, Matthew; Lunt, Daniel J.; Siler, Nicholas; Steinig, Sebastian; Tierney, Jessica E.; Wilkinson, Richard; Anagnostou, Eleni; de Boer, Agatha M.; Dunkley Jones, Tom (26 October 2020). "Global mean surface temperature and climate sensitivity of the early Eocene Climatic Optimum (EECO), Paleocene–Eocene Thermal Maximum (PETM), and latest Paleocene". Climate of the Past . 16 (5): 1953–1968. Bibcode:2020CliPa..16.1953I. doi: 10.5194/cp-16-1953-2020 . hdl: 1983/24a30f12-51a6-4544-9db8-b2009e33c02a . ISSN   1814-9332 . Retrieved 23 September 2023.
  18. Stap, L.; Lourens, L.J.; Thomas, E.; Sluijs, A.; Bohaty, S.; Zachos, J.C. (1 July 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.
  19. Bohaty, Steven M.; Zachos, James C. (1 November 2003). "Significant Southern Ocean warming event in the late middle Eocene". Geology . 31 (11): 1017. Bibcode:2003Geo....31.1017B. doi:10.1130/G19800.1. ISSN   0091-7613 . Retrieved 23 September 2023.
  20. Pearson, Paul N.; Foster, Gavin L.; Wade, Bridget S. (13 September 2009). "Atmospheric carbon dioxide through the Eocene–Oligocene climate transition". Nature . 461 (7267): 1110–1113. Bibcode:2009Natur.461.1110P. doi:10.1038/nature08447. ISSN   0028-0836. PMID   19749741. S2CID   205218274 . Retrieved 23 September 2023.
  21. Sauermilch, Isabel; Whittaker, Joanne M.; Klocker, Andreas; Munday, David R.; Hochmuth, Katharina; Bijl, Peter K.; LaCasce, Joseph H. (9 November 2021). "Gateway-driven weakening of ocean gyres leads to Southern Ocean cooling". Nature Communications . 12 (1): 6465. Bibcode:2021NatCo..12.6465S. doi:10.1038/s41467-021-26658-1. ISSN   2041-1723. PMC   8578591 . PMID   34753912.
  22. Barker, P.F.; Thomas, E. (June 2004). "Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current". Earth-Science Reviews . 66 (1–2): 143–162. Bibcode:2004ESRv...66..143B. doi:10.1016/j.earscirev.2003.10.003 . Retrieved 23 September 2023.
  23. Zachos, James C.; Lohmann, Kyger C.; Walker, James C. G.; Wise, Sherwood W. (March 1993). "Abrupt Climate Change and Transient Climates during the Paleogene: A Marine Perspective". The Journal of Geology . 101 (2): 191–213. Bibcode:1993JG....101..191Z. doi:10.1086/648216. ISSN   0022-1376. PMID   11537739. S2CID   29784731 . Retrieved 23 September 2023.
  24. Hochmuth, Katharina; Whittaker, Joanne M.; Sauermilch, Isabel; Klocker, Andreas; Gohl, Karsten; LaCasce, Joseph H. (9 November 2022). "Southern Ocean biogenic blooms freezing-in Oligocene colder climates". Nature Communications . 13 (1): 6785. Bibcode:2022NatCo..13.6785H. doi:10.1038/s41467-022-34623-9. ISSN   2041-1723. PMC   9646741 . PMID   36351905.
  25. 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.
  26. Crame, J. Alistair (March 2020). "Early Cenozoic evolution of the latitudinal diversity gradient". Earth-Science Reviews . 202: 103090. Bibcode:2020ESRv..20203090C. doi: 10.1016/j.earscirev.2020.103090 . S2CID   214219923.
  27. Traverse, Alfred (1988). Paleopalynology. Unwin Hyman. ISBN   978-0-04-561001-3. OCLC   17674795.
  28. Muller, Jan (January 1981). "Fossil pollen records of extant angiosperms". The Botanical Review. 47 (1): 1–142. Bibcode:1981BotRv..47....1M. doi:10.1007/bf02860537. ISSN   0006-8101. S2CID   10574478.