The OLIGOCENE ( /ˈɒlᵻɡoʊsiːn/ ) 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 comes from the Ancient Greek
ὀλίγος (oligos, "few") and καινός (kainos, "new"), and
refers to the sparsity of extant forms of molluscs . The
preceded by the
Eocene Epoch and is followed by the
Miocene Epoch. The
Oligocene is the third and final epoch of the
Oligocene is often considered an important time of transition, a
link between the archaic world of the tropical
Eocene and the more
modern ecosystems of the Miocene. Major changes during the Oligocene
included a global expansion of grasslands , and a regression of
tropical broad leaf forests to the equatorial belt .
The start of the
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 boundary is not set at
an easily identified worldwide event but rather at regional boundaries
between the warmer late
Oligocene and the relatively cooler Miocene.
* 1 Subdivisions
* 2 Climate
* 3 Paleogeography
* 4 Flora
* 6 Oceans
* 6.1 The effects of oceanic gateways on circulation
* 6.1.1 The
* 184.108.40.206 The late
Oligocene opening of the
* 220.127.116.11 The early
Oligocene opening of the
* 6.1.2 The opening of the Tasman Gateway
* 6.1.3 The Tethys Seaway closing
* 6.1.4 Greenland–Iceland–
* 6.2 Ocean cooling
* 6.3 Deep water
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
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)
Paleogene Period general temperature decline is interrupted by an
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). The stepwise climate change began 32.5 Ma and lasted through
to 25.5 Ma, as depicted in the PaleoTemps chart. The
change was a global 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. The 7-million-year
depression abruptly terminated within 1–2 million years of the La
Garita Caldera eruption at 28–26 Ma. A deep 400,000-year glaciated
Miocene boundary event is recorded at
McMurdo Sound and King
George Island .
Neotethys in oligocene (Rupelian, 33,9 — 28,4 mya)
During this epoch, the continents continued to drift toward their
Antarctica became more isolated and finally
developed an ice cap .
Mountain building in western
North America continued, and the Alps
started to rise in
Europe as the African plate continued to push north
Eurasian plate , isolating the remnants of the
Tethys Sea . A
brief marine incursion marks the early
Oligocene in Europe. Marine
fossils from the
Oligocene are rare in North America. There appears to
have been a land bridge in the early
Oligocene between North America
and Europe, since the faunas of the two regions are very similar.
Sometime during the Oligocene,
South America was finally detached from
Antarctica and drifted north towards
North America . It also allowed
Antarctic Circumpolar Current
Antarctic Circumpolar Current to flow, rapidly cooling the
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 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 , beeches ,
and pines were common. The legumes spread, while sedges , bulrushes ,
and ferns continued their ascent.
Oligocene fauna of
Even more open landscapes allowed animals to grow to larger sizes
than they had earlier in the
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 and spread to Europe. PYROTHERIUM
romeroi with the notoungulate
Reconstruction of Astrapotherium in natural habitat.
Macrauchenia : a
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
Africa and the
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 was home to a
wide variety of strange mammals. A good example of this would be the
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 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
The marine animals of
Oligocene oceans resembled today's fauna, such
as the bivalves . Calcareous cirratulids appeared in the Oligocene.
The fossil record of marine mammals is a little spotty during this
time, and not as well known as the
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 appeared near the end of the epoch
from an otter -like ancestor.
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, and they continued to cool as the
Oligocene progressed. The
formation of permanent Antarctic ice sheets during the early 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
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
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.
The Drake Passage
Drake Passage is located between
South America and
Once the Tasmanian Gateway between Australia and
all that kept
Antarctica from being completely isolated by the
Southern Ocean was its connection to South America. As the South
American continent moved north, the
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 circulating around that
continent and strengthened the formation of Antarctic Bottom Water
(ABW). 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, and the effect of the
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 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 and
Antarctica, permitting the start of an Antarctic Circumpolar Current.
Stemming from the issue of when the opening of the
Drake Passage took
place, is the dispute over how great of an influence the opening of
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 and subsequent global
cooling, other studies have suggested that the δ18O signature is too
strong for glaciation to be the main trigger for cooling. Through
study of Pacific Ocean sediments, other researchers have shown that
the transition from warm
Eocene ocean temperatures to cool Oligocene
ocean temperatures took only 300,000 years, which strongly implies
that feedbacks and factors other than the ACC were integral to the
Oligocene Opening Of The Drake Passage
The latest hypothesized time for the opening of the
Drake Passage is
during the early Miocene. 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
Oligocene cooling, as it would not have existed.
Oligocene Opening Of The Drake Passage
The earliest hypothesized time for the opening of the Drake Passage
is around 30 Ma. 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. 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
Currently, an opening of the
Drake Passage during the early Oligocene
The Opening Of The Tasman Gateway
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 and is largely considered to have
occurred around 34 Ma. As the gateway widened, the Antarctic
Circumpolar Current strengthened.
The Tethys Seaway Closing
The Tethys Seaway was not a gateway, but rather a sea in its own
right. Its closing during the
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. The closure of Tethys built some new mountains
(the Zagros range) and drew down more carbon dioxide from the
atmosphere, contributing to global cooling.
The gradual separation of the clump of continental crust and the
deepening of the tectonic sill in the
North Atlantic that would become
Greenland, Iceland, and the Faroe Islands helped to increase the deep
water flow in that area. More information about the evolution of
North Atlantic Deep Water will be given a few sections down.
Evidence for ocean-wide cooling during the
Oligocene exists mostly in
isotopic proxies. Patterns of extinction and patterns of species
migration can also be studied to gain insight into ocean conditions.
For a while, it was thought that the glaciation of
Antarctica may have
significantly contributed to the cooling of the ocean, however, recent
evidence tends to deny this.
Isotopic evidence suggests that during the early Oligocene, the main
source of deep water was the
North Pacific and the
Southern Ocean . As
the Greenland-Iceland-Faroe sill deepened and thereby connected the
Greenland sea with the Atlantic Ocean, the deep water of
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.
North Atlantic Deep Water
Evidence for the early
Oligocene onset of chilled
North Atlantic deep
water lies in the beginnings of sediment drift deposition in the North
Atlantic, such as the Feni and Southeast Faroe drifts.
South Ocean Deep Water
The chilling of the South Ocean deep water began in earnest once the
Tasmanian Gateway and the
Drake Passage opened fully. Regardless of
the time at which the opening of the
Drake Passage occurred, the
effect on the cooling of the
Southern Ocean would have been the same.
Recorded extraterrestrial impacts:
Haughton impact crater ,
Nunavut , Canada (23 Ma, crater 24 km (15
La Garita Caldera (28 through 26 million years ago,
List of fossil sites (with link directory)
* ^ Cohen, K.M.; Finney, S.; Gibbard, P.L. (2013), International
Chronostratigraphic Chart (PDF), International Commission on
* ^ "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
Oligocene in central North America' Nature, Vol. 445, 8
* ^ C.R.Riesselman (et al.) 2007 'High Resolution stable isotope
and carbonate variability during the early
transition: Walvis Ridge (ODPSite 1263) USGS OF-2007-1047
Lorraine E. Lisiecki Nov 2004; A Pliocene–
of 57 globally distributed benthic δ18O records Brown University,
PALEOCEANOGRAPHY, VOL. 20
* ^ Kenneth G. Miller Jan–Feb 2006; Eocene–
climate and sea-level changes St. Stephens Quarry, Alabama GSA
Bulletin, Rutgers University, NJ
* ^ 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
* ^ 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 evolution of climate". Reviews of
Geophysics. 46 (2): 1–47.
Bibcode :2008RvGeo..46.2002L. doi
* ^ A B C Prothero, D. (May 2005). "Tertiary to Present
Oligocene". Encyclopedia of Geology: 472–478. ISBN 978-0-12-369396-9
. doi :10.1016/B0-12-369396-9/00056-3 .
* ^ 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 onset of
deep-water production in the North Atlantic". Geology. 34 (6):
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
structure". Science. 332 (6033): 1076–1079. Bibcode
:2011Sci...332.1076K. PMID 21617074 . doi :10.1126/science.1202122 .
* ^ 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 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 sea surface
temperatures: An approach based on coral taxonomic richness".
Palaeogeography, Palaeoclimatology, Palaeobiology. 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 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.
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