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The Oligocene
Oligocene
( /ˈɒlɪɡoʊsiːn/) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present (7001339000000000000♠33.9±0.1 to 7014726771528000000♠23.03±0.05 Ma). 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
Oligocene
comes from the Ancient Greek ὀλίγος (olígos, "few") and καινός (kainós, "new"),[2] and refers to the sparsity of extant forms of molluscs. The Oligocene is preceded by the Eocene
Eocene
Epoch and is followed by the Miocene
Miocene
Epoch. The Oligocene
Oligocene
is the third and final epoch of the Paleogene Period. The Oligocene
Oligocene
is often considered an important time of transition, a link between the archaic world of the tropical Eocene
Eocene
and the more modern ecosystems of the Miocene.[3] Major changes during the Oligocene
Oligocene
included a global expansion of grasslands, and a regression of tropical broad leaf forests to the equatorial belt. The start of the Oligocene
Oligocene
is marked by a notable extinction event called the Grande Coupure; it featured the replacement of European fauna with Asian fauna, except for the endemic rodent and marsupial families. By contrast, the Oligocene– Miocene
Miocene
boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer late Oligocene
Oligocene
and the relatively cooler Miocene.

Contents

1 Subdivisions 2 Climate 3 Paleogeography 4 Flora 5 Fauna 6 Oceans

6.1 The effects of oceanic gateways on circulation

6.1.1 The Drake Passage

6.1.1.1 The late Oligocene
Oligocene
opening of the Drake Passage 6.1.1.2 The early Oligocene
Oligocene
opening of the Drake Passage

6.1.2 The opening of the Tasman Gateway 6.1.3 The Tethys Seaway closing 6.1.4 Greenland–Iceland–Faroes

6.2 Ocean cooling 6.3 Deep water

6.3.1 North Atlantic
North Atlantic
deep water 6.3.2 South Ocean deep water

7 Impact events 8 Supervolcanic explosions 9 See also 10 References 11 External links

Subdivisions[edit] Oligocene
Oligocene
faunal stages from youngest to oldest are:

Chattian or late Oligocene  (28.1  –  23.03 mya)

Rupelian or early Oligocene  (33.9  –  28.1 mya)

Climate[edit]

The Paleogene Period general temperature decline is interrupted by an Oligocene
Oligocene
7-million-year stepwise climate change. A deeper 8.2 °C, 400,000-year temperature depression leads the 2 °C, seven-million-year stepwise climate change 33.5 Ma (million years ago).[4][5] The stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene
Oligocene
climate change was a global[6] increase in ice volume and a 55 m (181 feet) decrease in sea level (35.7–33.5 Ma) with a closely related (25.5–32.5 Ma) temperature depression.[7] The 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera
La Garita Caldera
eruption at 28–26 Ma. A deep 400,000-year glaciated Oligocene
Oligocene
Miocene
Miocene
boundary event is recorded at McMurdo Sound
McMurdo Sound
and King George Island. Paleogeography[edit]

Neotethys
Neotethys
in oligocene (Rupelian, 33,9 — 28,4 mya)

During this epoch, the continents continued to drift toward their present positions. Antarctica
Antarctica
became more isolated and finally developed an ice cap. Mountain building in western North America
North America
continued, and the Alps started to rise in Europe
Europe
as the African plate continued to push north into the Eurasian plate, isolating the remnants of the Tethys Sea. A brief marine incursion marks the early Oligocene
Oligocene
in Europe. Marine fossils from the Oligocene
Oligocene
are rare in North America. There appears to have been a land bridge in the early Oligocene
Oligocene
between North America and Europe, since the faunas of the two regions are very similar. Sometime during the Oligocene, South America
South America
was finally detached from Antarctica
Antarctica
and drifted north towards North America. It also allowed the Antarctic Circumpolar Current
Antarctic Circumpolar Current
to flow, rapidly cooling the Antarctic continent. Flora[edit] Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by temperate deciduous forests. Open plains and deserts became more common and grasses expanded from their water-bank habitat in the Eocene
Eocene
moving out into open tracts. However, even at the end of the period, grass was not quite common enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, and temperate trees such as roses,[clarification needed] beeches, and pines were common. The legumes spread, while sedges, bulrushes, and ferns continued their ascent. Fauna[edit]

Restoration of Oligocene
Oligocene
fauna of North America

Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene
Paleocene
epoch 30 million years earlier. Marine faunas became fairly modern, as did terrestrial vertebrate fauna on the northern continents. This was probably more as a result of older forms dying out than as a result of more modern forms evolving. Many groups, such as equids, entelodonts, rhinos, merycoidodonts, and camelids, became more able to run during this time, adapting to the plains that were spreading as the Eocene rainforests receded. The first felid, Proailurus, originated in Asia during the late Oligocene
Oligocene
and spread to Europe.[8]

Pyrotherium
Pyrotherium
romeroi with the notoungulate Rhynchippus
Rhynchippus
equinus

Reconstruction of Astrapotherium in natural habitat.

Macrauchenia: a Litoptern

South America
South America
was isolated from the other continents and evolved a quite distinct fauna during the Oligocene. The South American continent became home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchians, terror birds, and carnivorous metatheres, like the borhyaenids remained the dominant predators. Brontotheres died out in the Earliest Oligocene, and creodonts died out outside Africa
Africa
and the Middle East
Middle East
at the end of the period. Multituberculates, an ancient lineage of primitive mammals that originated back in the Jurassic, also became extinct in the Oligocene, aside from the gondwanatheres. The Oligocene
Oligocene
was home to a wide variety of strange mammals. A good example of this would be the White River Fauna
Fauna
of central North America, which were formerly a semiarid prairie home to many different types of endemic mammals, including entelodonts like Archaeotherium, camelids (such as Poebrotherium), running rhinoceratoids, three-toed equids (such as Mesohippus), nimravids, protoceratids, and early canids like Hesperocyon. Merycoidodonts, an endemic American group, were very diverse during this time. In Asia
Asia
during the Oligocene, a group of running rhinoceratoids gave rise to the indricotheres, like Paraceratherium, which were the largest land mammals ever to walk the Earth. The marine animals of Oligocene
Oligocene
oceans resembled today's fauna, such as the bivalves. Calcareous cirratulids appeared in the Oligocene.[9] The fossil record of marine mammals is a little spotty during this time, and not as well known as the Eocene
Eocene
or Miocene, but some fossils have been found. The baleen whales and toothed whales had just appeared, and their ancestors, the archaeocete cetaceans began to decrease in diversity due to their lack of echolocation, which was very useful as the water became colder and cloudier. Other factors to their decline could include climate changes and competition with today's modern cetaceans and the carcharhinid sharks, which also appeared in this epoch. Early desmostylians, like Behemotops, are known from the Oligocene. Pinnipeds
Pinnipeds
appeared near the end of the epoch from an otter-like ancestor.[10] Oceans[edit] The Oligocene
Oligocene
sees the beginnings of modern ocean circulation, with tectonic shifts causing the opening and closing of ocean gateways. Cooling of the oceans had already commenced by the Eocene/Oligocene boundary,[11] and they continued to cool as the Oligocene
Oligocene
progressed. The formation of permanent Antarctic ice sheets during the early Oligocene
Oligocene
and possible glacial activity in the Arctic may have influenced this oceanic cooling, though the extent of this influence is still a matter of some significant dispute. The effects of oceanic gateways on circulation[edit] The opening and closing of ocean gateways: the opening of the Drake Passage; the opening of the Tasmanian Gateway and the closing of the Tethys seaway; along with the final formation of the Greenland–Iceland– Faroes
Faroes
sill; played vital parts in reshaping oceanic currents during the Oligocene. As the continents shifted to a more modern configuration, so too did ocean circulation.[12] The Drake Passage[edit] The Drake Passage
Drake Passage
is located between South America
South America
and Antarctica. Once the Tasmanian Gateway between Australia and Antarctica
Antarctica
opened, all that kept Antarctica
Antarctica
from being completely isolated by the Southern Ocean
Southern Ocean
was its connection to South America. As the South American continent moved north, the Drake Passage
Drake Passage
opened and enabled the formation of the Antarctic Circumpolar Current
Antarctic Circumpolar Current
(ACC), which would have kept the cold waters of Antarctica
Antarctica
circulating around that continent and strengthened the formation of Antarctic Bottom Water (ABW).[12][13] With the cold water concentrated around Antarctica, sea surface temperatures and, consequently, continental temperatures would have dropped. The onset of Antarctic glaciation occurred during the early Oligocene,[14] and the effect of the Drake Passage
Drake Passage
opening on this glaciation has been the subject of much research. However, some controversy still exists as to the exact timing of the passage opening, whether it occurred at the start of the Oligocene
Oligocene
or nearer the end. Even so, many theories agree that at the Eocene/Oligocene (E/O) boundary, a yet shallow flow existed between South America
South America
and Antarctica, permitting the start of an Antarctic Circumpolar Current.[15] Stemming from the issue of when the opening of the Drake Passage
Drake Passage
took place, is the dispute over how great of an influence the opening of the Drake Passage
Drake Passage
had on the global climate. While early researchers concluded that the advent of the ACC was highly important, perhaps even the trigger, for Antarctic glaciation[12] and subsequent global cooling, other studies have suggested that the δ18O signature is too strong for glaciation to be the main trigger for cooling.[15] Through study of Pacific Ocean sediments, other researchers have shown that the transition from warm Eocene
Eocene
ocean temperatures to cool Oligocene ocean temperatures took only 300,000 years,[11] which strongly implies that feedbacks and factors other than the ACC were integral to the rapid cooling.[11] The late Oligocene
Oligocene
opening of the Drake Passage[edit] The latest hypothesized time for the opening of the Drake Passage
Drake Passage
is during the early Miocene.[11] Despite the shallow flow between South America and Antarctica, there was not enough of a deep water opening to allow for significant flow to create a true Antarctic Circumpolar Current. If the opening occurred as late as hypothesized, then the Antarctic Circumpolar Current
Antarctic Circumpolar Current
could not have had much of an effect on early Oligocene
Oligocene
cooling, as it would not have existed. The early Oligocene
Oligocene
opening of the Drake Passage[edit] The earliest hypothesized time for the opening of the Drake Passage
Drake Passage
is around 30 Ma.[11] One of the possible issues with this timing was the continental debris cluttering up the seaway between the two plates in question. This debris, along with what is known as the Shackleton Fracture Zone, has been shown in a recent study to be fairly young, only about 8 million years old.[13] The study concludes that the Drake Passage would be free to allow significant deep water flow by around 31 Ma. This would have facilitated an earlier onset of the Antarctic Circumpolar Current. Currently, an opening of the Drake Passage
Drake Passage
during the early Oligocene is favored. The opening of the Tasman Gateway[edit] The other major oceanic gateway opening during this time was the Tasman, or Tasmanian, depending on the paper, gateway between Australia and Antarctica. The time frame for this opening is less disputed than the Drake Passage
Drake Passage
and is largely considered to have occurred around 34 Ma. As the gateway widened, the Antarctic Circumpolar Current strengthened. The Tethys Seaway closing[edit] The Tethys Seaway was not a gateway, but rather a sea in its own right. Its closing during the Oligocene
Oligocene
had significant impact on both ocean circulation and climate. The collisions of the African plate with the European plate and of the Indian subcontinent with the Asian plate, cut off the Tethys Seaway that had provided a low-latitude ocean circulation.[16] The closure of Tethys built some new mountains (the Zagros range) and drew down more carbon dioxide from the atmosphere, contributing to global cooling.[17] Greenland–Iceland–Faroes[edit] The gradual separation of the clump of continental crust and the deepening of the tectonic sill in the North Atlantic
North Atlantic
that would become Greenland, Iceland, and the Faroe Islands helped to increase the deep water flow in that area.[14] More information about the evolution of North Atlantic
North Atlantic
Deep Water will be given a few sections down. Ocean cooling[edit] Evidence for ocean-wide cooling during the Oligocene
Oligocene
exists mostly in isotopic proxies. Patterns of extinction[18] and patterns of species migration[19] can also be studied to gain insight into ocean conditions. For a while, it was thought that the glaciation of Antarctica
Antarctica
may have significantly contributed to the cooling of the ocean, however, recent evidence tends to deny this.[13][20] Deep water[edit] Isotopic evidence suggests that during the early Oligocene, the main source of deep water was the North Pacific
North Pacific
and the Southern Ocean. As the Greenland-Iceland-Faroe sill deepened and thereby connected the Norwegian– Greenland
Greenland
sea with the Atlantic Ocean, the deep water of the North Atlantic
North Atlantic
began to come into play as well. Computer models suggest that once this occurred, a more modern in appearance thermo-haline circulation started.[16] North Atlantic
North Atlantic
deep water[edit] Evidence for the early Oligocene
Oligocene
onset of chilled North Atlantic
North Atlantic
deep water lies in the beginnings of sediment drift deposition in the North Atlantic, such as the Feni and Southeast Faroe drifts.[14] South Ocean deep water[edit] The chilling of the South Ocean deep water began in earnest once the Tasmanian Gateway and the Drake Passage
Drake Passage
opened fully.[13] Regardless of the time at which the opening of the Drake Passage
Drake Passage
occurred, the effect on the cooling of the Southern Ocean
Southern Ocean
would have been the same. Impact events[edit] Recorded extraterrestrial impacts:

Haughton impact crater, Nunavut, Canada (23 Ma, crater 24 km (15 mi) diameter)

Supervolcanic explosions[edit] La Garita Caldera
La Garita Caldera
(28 through 26 million years ago, VEI=9.2)[21] See also[edit]

List of fossil sites
List of fossil sites
(with link directory) Turgai Sea

References[edit]

^ "ICS - Chart/Time Scale". www.stratigraphy.org.  ^ "Oligocene". Online Etymology Dictionary.  ^ Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999) ^ A.Zanazzi (et al.) 2007 'Large Temperature Drop across the Eocene Oligocene
Oligocene
in central North America' Nature, Vol. 445, 8 February 2007 ^ C.R.Riesselman (et al.) 2007 'High Resolution stable isotope and carbonate variability during the early Oligocene
Oligocene
climate transition: Walvis Ridge (ODPSite 1263) USGS OF-2007-1047 ^ Lorraine E. Lisiecki Nov 2004; A Pliocene– Pleistocene
Pleistocene
stack of 57 globally distributed benthic δ18O records Brown University, PALEOCEANOGRAPHY, VOL. 20 ^ Kenneth G. Miller Jan–Feb 2006; Eocene– Oligocene
Oligocene
global climate and sea-level changes St. Stephens Quarry, Alabama GSA Bulletin, Rutgers University, NJ [1] ^ Mott, Maryann (2006-01-11). "Cats Climb New family Tree". National Geographic News. Retrieved 2006-07-15.  ^ Vinn, O. (2009). "The ultrastructure of calcareous cirratulid (Polychaeta, Annelida) tubes" (PDF). Estonian Journal of Earth Sciences. 58 (2): 153–156. doi:10.3176/earth.2009.2.06. Retrieved 2012-09-16.  ^ Handwerk, Brian (2009-03-22). "Seal with "Arms" Discovered". National Geographic News. Retrieved 2014-12-31.  ^ a b c d e Lyle, Mitchell; Barron, J.; Bralower, T.; Huber, M.; Olivarez Lyle, A.; Ravelo, A. C.; Rea, D. K.; Wilson, P. A. (April 2008). "Pacific Ocean and Cenozoic
Cenozoic
evolution of climate". Reviews of Geophysics. 46 (2): 1–47. Bibcode:2008RvGeo..46.2002L. doi:10.1029/2005RG000190.  ^ a b c Prothero, D. (May 2005). "Tertiary to Present Oligocene". Encyclopedia of Geology: 472–478. doi:10.1016/B0-12-369396-9/00056-3. ISBN 978-0-12-369396-9.  ^ a b c d Mackensen, Andreas (Dec 2004). "Changing Southern Ocean palaeocirculation and effects on global climate". Antarctic Science. 16 (4): 369–389. doi:10.1017/S0954102004002202.  ^ a b c Via, Rachael; Thomas, D. (June 2006). "Evolution of Antarctic thermohaline circulation: Early Oligocene
Oligocene
onset of deep-water production in the North Atlantic". Geology. 34 (6): 441–444. Bibcode:2006Geo....34..441V. doi:10.1130/G22545.1.  ^ a b Katz, M; Cramer, B.; Toggweiler, J.; Esmay, G.; Liu, C.; Miller, K.; Rosenthal, Y.; Wade, B.; Wright, J. (May 2011). "Impact of Antarctic Circumpolar Current
Antarctic Circumpolar Current
development on late Paleogene ocean structure". Science. 332 (6033): 1076–1079. Bibcode:2011Sci...332.1076K. doi:10.1126/science.1202122. PMID 21617074.  ^ a b von der Heydt, Anna; Dijkstra, Henk A. (May 2008). "The effect of gateways on ocean circulation patterns in the Cenozoic". Global and Planetary Changes. 1-2. 62: 132–146. Bibcode:2008GPC....62..132V. doi:10.1016/j.gloplacha.2007.11.006.  ^ Allen, Mark; Armstrong, Howard (July 2008). "Arabia-Eurasia cooling and the forcing of mid- Cenozoic
Cenozoic
global cooling". Palaeogeology, Palaeoclimatology, Palaeoecology. 1-2. 265: 52–58. doi:10.1016/j.palaeo.2008.04.021.  ^ Green, William; Hunt, G.; Wing, S.; DiMichele, W. (2011). "Does extinction wield an axe or pruning shears? How interactions between phylogeny and ecology affect patterns of extinction". Paleobiology. 37 (1): 72–91. doi:10.1666/09078.1.  ^ Bosellini, Francesca; Perrin, Christine (February 2008). "Estimating Mediterranean Oligocene– Miocene
Miocene
sea surface temperatures: An approach based on coral taxonomic richness". Palaeogeography, Palaeoclimatology, Palaeoecology. 1-2. 258: 71–88. doi:10.1016/j.palaeo.2007.10.028.  ^ Hay, William; Flogel, S.; Soding, E. (September 2004). "Is initiation of glaciation on Antarctica
Antarctica
related to a change in the structure of the ocean?". Global and Planetary Change. 1-3. 45: 1–11. doi:10.1016/j.gloplacha.2004.09.005.  ^ Breining, Greg (2007). "Most-Super Volcanoes". Super Volcano: The Ticking Time Bomb Beneath Yellowstone National Park. St. Paul, MN: Voyageur Press. pp. 256 pg. ISBN 978-0-7603-2925-2. 

Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.

External links[edit]

Wikimedia Commons has media related to Oligocene.

Wikisource has original works on the topic: Cenozoic#Paleogene

Paleos: Oligocene UCMP Berkeley Oligocene
Oligocene
Page Prehistoric Pictures, in the Public Domain Oligocene
Oligocene
Leaf Fossils Olicgocene Fish Fossils PaleoMap Project: Oligocene Oligocene
Oligocene
Microfossils: 300+ images of Foraminifera

v t e

Paleogene Period

Paleocene
Paleocene
Epoch Eocene
Eocene
Epoch Oligocene
Oligocene
Epoch

Danian Selandian Thanetian

Ypresian Lutetian Bartonian Priabonian

Rupelian Chattian

v t e

Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–251.902 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–251.902 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–251.902 Mya)

Paleozoic
Paleozoic
era¹ (251.902–541.0 Mya)

Permian
Permian
(251.902–298.9 Mya)

Lopingian
Lopingian
(251.902–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow (423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery (433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2017/02). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013.

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