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System Series Stage Age (Ma)
Neogene Miocene Aquitanian younger
Paleogene Oligocene Chattian 23.03–28.4
Rupelian 28.4–33.9
Eocene Priabonian 33.9–37.2
Bartonian 37.2–40.4
Lutetian 40.4–48.6
Ypresian 48.6–55.8
Paleocene Thanetian 55.8–58.7
Selandian 58.7–61.7
Danian 61.7–65.5
Cretaceous Upper Maastrichtian older
Subdivision of the Paleogene Period according to the IUGS, as of July 2009.

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present (33.9 ± 0.1 to 23.03 ± 0.05 Ma). As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene comes from the Greek ὀλίγος (oligos, few) and καινός (kainos, new), and refers to the sparsity of additional modern mammalian faunas after a burst of evolution during the Eocene. The Oligocene follows the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.

The Oligocene is often considered an important time of transition, a link between "[the] archaic world of the tropical Eocene and the more modern-looking ecosystems of the Miocene."[1] 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 major extinction event, a faunal replacement of European with Asian fauna except for the endemic rodent and marsupial families called the Grande Coupure. 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.

Contents

Subdivisions

Oligocene faunal stages from youngest to oldest are:

Chattian or Late Oligocene (28.4 ± 0.1 – 23.03 mya)
Rupelian or Early Oligocene (33.9 ± 0.1 – 28.4 ± 0.1 mya)

Climate

All palaeotemps.png

The Paleogene Period general temperature decline is interrupted by an Oligocene 7M-year stepwise climate change. A deeper 8.2oC 0.4M-year temperature depression leads the 2oC 7M-year stepwise climate change 33.5Ma.[2][3] The stepwise climate spanned 7M-years 25.5Ma through 32.5Ma as depicted in the PaleoTemps chart. The Oligocene climate change was a global [4] increase in ice volume and a 55m decrease in sea level (35.7-33.5Ma) with a closely related (25.5-32.5Ma) temperature depression.[5] The 7M-year depression abruptly terminated within 1-2M-year of the La Garita Caldera volcanism event 28-26 Ma. A deep 400 k-year glaciating Oligocene Miocene boundary event is recorded at the McMurdo Sound and King George Island.

Paleogeography

During this period, the continents continued to drift toward their present positions. Antarctica continued to become more isolated and finally developed a permanent ice cap.(Haines)

Mountain building in western North America continued, and the Alps started to rise in 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 in Europe. Oligocene marine exposures 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. During sometime in the Oligocene, South America was finally detached from Antarctica and drifted north towards North America. It also allowed the Antarctic Circumpolar Current to flow, rapidly cooling the continent.

Flora

Angiosperms continued their expansion throughout the world; tropical and sub-tropical forests were replaced by temperate deciduous woodlands. Open plains and deserts became more common. Grasses expanded from the water-bank habitat in the Eocene and moved out into open tracts; however even at the end of the period it was not quite common enough for modern savanna.(Haines)

In North America, subtropical species dominated with cashews and lychee trees present, and temperate trees such as roses, beech and pine were common. The legumes of the pea and bean family spread, and sedges, bulrushes and ferns continued their ascent.

Fauna

Important Oligocene land faunas are found on all continents except Australia. Even more open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleogene. Marine faunas became fairly modern, as did terrestrial vertebrate faunas in 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 during this time, such as horses, entelodonts, rhinoceroses, oreodonts, and camels, became more cursorial during this time, adapting to the plains that were spreading as the Eocene rainforests receded.

South America was isolated from the other continents and evolved a quite distinct fauna during the Oligocene, home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchian crocodiles, terror birds, and carnivorous marsupials like the borhyaenids remained the dominant predators. Brontotheres died out in the Earliest Oligocene, and creodonts died out outside Africa and the Middle East at the end of the period. Multituberculates, an ancient lineage of primitive mammals, also went extinct in the Oligocene. The Oligocene was home to a wide variety of strange mammals. A good example of this would be in the White River Badlands of the United States, which were formerly a semi-arid prairie home to many different types of endemic mammals, including entelodonts like Archaeotherium, camels (such as Poebrotherium), running rhinos, three-toed horses (such as Mesohippus), nimravids, protoceratids, and early dogs like Hesperocyon. Oreodonts, an endemic American group, were very diverse during this time. In Asia during the Oligocene, a group of running rhinos gave rise to the indricotheres, like Indricotherium, which were the largest land mammals ever to walk the Earth.

The marine animals of Oligocene oceans resembled today's fauna, such as the bivalves. 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 and toothed cetaceans (whales) 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 probably appeared near the end of the epoch from a bear-like or otter-like ancestor.

Oceans

Oceans continued to cool, particularly around Antarctica.

Impact events

Recorded extraterrestrial impacts:

  • Nunavut, Canada (23 Ma, crater 24 km diameter,)

Supervolcanic explosions

La Garita Caldera (28 through 26 million years ago, VEI=9.2)[6]

See also

References

  1. ^ Haines, Tim; Walking with Beasts: A Prehistoric Safari, (New York: Dorling Kindersley Publishing, Inc., 1999)
  2. ^ A.Zanazzi (et al.) 2007 'Large Temperature Drop across the Eocene Oligocene in central North America' Nature, Vol. 445, 8 February 2007
  3. ^ C.R.Riesselman (et al.) 2007 'High Resolution stable isotope and carbonate variability during the early Oligocene climate transition: Walvis Ridge (ODP Site 1263) USGS OF-2007-1047
  4. ^ Lorraine E. Lisiecki Nov 2004; A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records Brown University, PALEOCEANOGRAPHY, VOL. 20
  5. ^ Kenneth G. Miller Jan-Feb 2006; Eocene–Oligocene global climate and sea-level changes St. Stephens Quarry, Alabama GSA Bulletin, Rutgers University, NJ [1]
  6. ^ 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. 

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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

OLIGOCENE SYSTEM (from the Gr. OXi'yos, few, and rcatvos, recent), in geology, the name given to the second division of the older Tertiary rocks, viz. those which occur above the Eocene and below the Miocene strata. These rocks were originally classed by Sir C. Lyell as " older Miocene," the term Oligocene being proposed by H. E. Beyrich in 1854 and again in 1858. Following A. de Lapparent, the Oligocene is here regarded as divisible into two stages, an upper one, the Etampian (from Etampes), equivalent to the Rupelian of A. Dumont (1849), and a lower one, the Sannoisian (from Sannois near Paris), equivalent to the Tongrian (from Tongris in Limburg) of Dumont (1859). This lower division is the Ligurian of some authors, and corresponds with the Lattorfian (Latdorf) of K. Mayer in north Germany; it is in part the equivalent of the older term Ludian of de Lapparent. It should be pointed out that several authors retain the Aquitanian stage (see Miocene) at the top of the Oligocene, but there are sufficiently good reasons for removing it to the younger system.

The Oligocene deposits are of fresh-water, brackish, marine and terrestrial origin; they include soft sands, sandstones, grits, marls, shales, limestones, conglomerates and lignites. The geographical aspect of Europe during this period is indicated on the accompanying map. Here and there, as in N. Germany, the sea gained ground that had been unoccupied by Eocene waters, but important changes, associated with the continuation of elevatory processes in the Pyrenees and Alps which had begun in the preceding period, were in progress, and a general relative uplifting took place which caused much of the Eocene sea floor to be occupied at this time by lake basins and lagoons. The movements, however, were not all of a negative character as regards the water areas, for oscillations were evidently frequent, and subsidence must .have been considerable in some regions to admit of the accumulation of the great thickness of material found deposited there. Perhaps the most striking change from Eocene topography in Europe is to be seen in the extension of the Oligocene sea over North Germany, whence it extended eastward through Poland and Russia to the AralCaspian region, communicating thence with Arctic waters by way of a Ural depression. The Asian extension of the central mediterranean sea appears to have begun to be limited. It was later in the period when the wide-spread emersion set in.

In Britain Oligocene formations are found only in the Hampshire Basin and the Isle of Wight; from the admixture of fresh-water, marine and estuarine deposits, E. Forbes named these the " Fluviomarine series." The following are the more important subdivisions, in descending order: The Hamstead (Hampstead) beds, marine at the top, with Ostrea callifera, Natica, &c., estuarine and freshwater below, with Unio, Viviparus and the remains of crocodiles, turtles and mammals. The Bembridge marls, fresh-water, estuarine and marine, resting upon the Bembridge limestone, with many fresh-water fossils such as Limnaea, Planorbis, Chara, large land snails, Amphidromus, Helix, Glandina, and many insects and plant leaves. The Osborne beds, marls, clays and limestones, with Unio, Limnaea, &c. The Headon beds (upper), fresh-water clays, marls and limestones (middle), brackish and marine, more sandy (lower), brackish and fresh-water clays, marls, tufaceous limestones and sandstones. The clays and sands of the Bovey Basin in Devonshire were formerly classed as Miocene, but they are now regarded by C. Reid as Eocene on the evidence of the plant remains, though there is still a possibility that they may be found to be of Oligocene age.

In France the best-known tract of Oligocene rocks rests in the Paris basin in close relationship with the underlying Eocene. These rocks include the first and second gypsum beds, the source of " plaster of Paris "; at Montmartre the first or upper bed is 20 metres in thickness, and some of the beds contain siliceous nodules (fusils) and numerous mammalian remains. Above the gypsum beds is the travertine of Champigny-sun-Marne, a series of blue and white marls (supra-gypseous marls), followed by the " glaises vents " or greenish marls. At the top of the lower Oligocene of this district is the lacustrine " calcaire de Brie " or middle travertine, which at Fertesous-Jouane is exploited for millstones; this is associated with the Fontainebleau limestone, which at Chateau-Landon and Souppes is sufficiently compact to form an important building stone, used in the Arc de Triomphe and other structures in Paris. The upper Oligocene of Paris begins with the marnes a huitres, followed by the brackish and fresh-water molasse of Etrechy, and a series of sandy beds, of which the best known are those of Fontainebleau, Etampes and Ormoy; in these occur the groups of calcite crystals, charged with sand, familiar in all mineral collections. Elsewhere in France similar mixed marine, fresh-water and brackish beds are found: in Aquitaine there are marine and lacustrine marls, limestones and molasse; marine beds occur at Biarritz; lacustrine and fresh-water marls and limestones with lignite appear in the sub-Pyrenees; in Provence there are brackish red clays, conglomerates and lignites, with limestones in the upper parts; and in Limagne there are mottled sands, arkoses; clays and fresh-water limestones. In the Jura region and on the borders of the central massif a peculiar group of deposits, the terrain siderolithique, is found in beds and in pockets in. Jurassic limestones. Sometimes this deposit consists of red clay (bolus) with nests of pisolitic iron, as in Jura and Franche-comte, Alsace, &c.;. occasionally, as in Bourgogne, Berry, the valley of the Aubois, Chatillon, it is made up of a breccia or conglomerate of Jurassic pebbles cemented with limonite and carbonate of lime or silica (an intimate mixture of marl and iron ore in these districts is called " castillard "). At Quercy the cementing material is phosphate of lime derived from the bones of mammals (Adapis, Necrolemur, Palaeotherium, Xiphodon, &c.), which are so numerous that it has been suggested that these animals must have been suffocated by gaseous emanations. Similar ferruginous deposits occur in South Germany.

In the Alpine region the Oligocene rocks assume the character of the Flysch, a complex assemblage of manly and sandy shales and soft sandstones with calcareous cement (" macigno "). The Flysch phase of deposition had begun before the close of the preceding period, but the bulk of it belongs to the Oligocene, and is especially characteristic of the lower part. The Flysch may attain a very great thickness; in Dauphine it is said to be 2000 metres. Obscure plantlike impressions are common on certain horizons of this formation, and have received such names as Chondrites, Fucoids, Helminthoidea. The " gres de Taveyannaz " and " Wildflysch " of Lake Thun contain fragments of eruptive rocks. Marine beds occur at Barreme, Desert, Chambery, &c., and parallel with the normal Flysch in the higher Alps of Vaudois is a nummulitic limestone; both here and near Interlaken, in the marble of Ralligstocke, calcareous algae are abundant. Part of the " schistes des Grisons " (" Biindner Schiefer ") have been regarded as of Oligocene age. In the Leman region the " Flysch rouge " at the foot of the Dent du Midi belongs to the upper part of the Flysch formation.

In North Germany the lower Oligocene consists largely of sandy marls, often glauconitic; typical localities are Egeln near Magdeburg and Latdorf near Bernburg; at Samland the glauconitic sand contains nodules of amber, with insects, derived from Eocene strata. The upper Oligocene beds, which cover a wide area, comprise the Stettin sands and Septarian Clay or Rupelton, marine beds tending to merge laterally one into another. In the Mainz basin a petroleumbearing sandy marl is found at Pechelbronn and Lobsann in Alsace underlying a fresh-water limestone which is followed by the marine tt Meeressand " of Alzey. Lignites (Braunkohl) are widely spread in this region and appear at Latdorf, Leipzig, in Westphalia and Mecklenburg; at Halle is a variety called pyropissite, which is exploited at Weissenfels for the manufacture of paraffin.

Map of Europe in the early cart of the Oligocene Period In Belgium a sandy series (Wemmelian, Asschian, Henisian), mainly of brackish-water origin, is succeeded by the marine sands of Bergh (with the clay of Boom), which pass up through the inferior sands of Bolderberg into the Miocene. In Switzerland, beyond the limits of the Flysch, nearer the Alpine massif, is a belt of grits, limestones and clays in. an uncompacted condition, to which the name "molasse " is usually given; mixed with the molasse is an inconstant conglomeratic littoral formation, called Nagelfluh. The molasse occurs also in Bavaria, where it is several thousand feet thick and contains lignites. Oligocene deposits occur in the Carpathian region and Tirol; as Flysch and brackish and lacustrine beds with lignite in Klausenburg, lignites at Haring in Tirol. In the Spanish Pyrenees they are well developed; in the Apennines the scaly clays (" argille scagliose ") are of this age; while in Calabria they are represented by thick conglomerates and Flysch. Flysch appears also in Dalmatia and Istria (where it is called " tassello ") and in North Bosnia, where it contains marine limestones. Lignites are found at Sotzka and Styria, marine beds in the Balkan peninsula, glauconitic sands prevail in South Russia, Flysch with sands and grits in the Caucasus, while marine deposits also occupy the Aral-Caspian region and Armenia, and are to be traced into Persia. Oligocene rocks are known in North Africa, Algeria, Tunis and Egypt, with the silicified trees and basalt sheets north of the Fayum. In North America the rocks of this period have not been very clearly differentiated, but they may possibly be represented by the White river beds of S. Dakota, the white and blue marls of Jackson on the Mississippi, the " Jacksonian " white limestone of Alabama, the limestone of Ocala in Florida, certain lacustrine clays in the Uinta basin, and by the ribband shales with asphalt and petroleum in the coastal range of California. In South America and the Antilles upper Oligocene is found, and the lignite beds of Coronel and Lota in Chile and in the Straits of Magellan may be of this age; in Patagonia are the lower Oligocene marine beds (" Patagonian ") and beds with mammalian remains. In New Zealand the Oamaru series of J. Hutton is regarded as Oligocene; at its base are interstratified basic volcanic rocks.

A correlation of Oligocene strata is summarized in the following table: - in the Eocene seas (Coelopleurus, Echinolampus, Clypeaster, Scutella). Corals were abundant, and nummulites still continued till near the close of the period, but they were diminished in size.

REFERENCES. - " Geology of the Isle of Wight," Mem. Geol. Survey (2nd ed. 1889); A. von Koenen, Abhand. geol. Specialkart Preuss. x. (1889-1894); M. Vollest, Der Braunkohlenbergbaum (Halle, 1889); E. van den Brocek, " Materiaux pour l'etude de l'Oligocene beige," Bull. Soc. Belg. Geol. (1894); also the works of O. Heer, H. Filhol, G. Vasseur, H. F. Osborn, A. Gaudry, H. Douville, R. B. Newton, H. Dall, M. Cossmann, G. Lambert, &c., and the article FLYSCH. (J. A. H.)


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