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OLIGOCENE See also:SYSTEM (from the Gr. oXiyos, few, and Katvbs, See also:recent) , in See also:geology, the name given to the second See also:division of the older See also:Tertiary rocks, viz. those which occur above the See also:Eocene and below the See also:Miocene strata . These rocks were originally classed by See also:Sir C . See also:Lyell as " older Miocene," the See also:term Oligocene being proposed by H . E . See also:Beyrich in 1854 and again in 1858 . Following A. de See also:Lapparent, the Oligocene is here regarded as divisible into two stages, an upper one, the Etampian (from See also:Etampes), See also:equivalent to the Rupelian of A . See also:Dumont (1849), and a See also:lower one, the Sannoisian (from Sannois near See also:Paris), equivalent to the Tongrian (from Tongris in See also:Limburg) of Dumont (1859) . This lower division is the Ligurian of some authors, and corresponds with the Lattorfian (Latdorf) of K . See also:Mayer in See also:north See also:Germany; it is in See also:part the equivalent of the older term Ludian of de Lapparent . It should be pointed out that several authors retain the Aquitanian See also:stage (see MIOCENE) at the See also:top of the Oligocene, but there are sufficiently See also:good reasons for removing it to the younger See also:system . The Oligocene deposits are of fresh-See also:water, brackish, marine and terrestrial origin; they include soft sands, sandstones, grits, marls, shales, limestones, conglomerates and lignites . The See also:geographical aspect of See also:Europe during this See also:period is indicated on the accompanying See also:map .
Here and there, as in N
.
Germany,
aher A.de Lapparcpt Emory See also:
See also:Reid as Eocene on the See also:evidence of the plant remains, though there is still a possibility that they may be found to be of Oligocene See also:age
.
In See also:France the best-known See also:tract of Oligocene rocks rests in the Paris basin in See also:close relationship with the underlying Eocene
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These rocks include the first and second See also:gypsum beds, the source of " See also:plaster of Paris "; at Montmartre the first or upper See also: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-sur-See also:Marne, a series of See also:blue and See also: 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 See also:Dauphine it is said to be 2000 metres . Obscure plant-like impressions are See also:common on certain horizons of this formation, and have received such names as Chondrites, Fucoids, Helminthoidea . The " gres de Taveyannaz " and " Wildflysch " of Lake See also:Thun contain fragments of eruptive rocks . Marine beds occur at Barreme, See also:Desert, See also:Chambery, &c., and parallel with the normal Flysch in the higher Alps of Vaudois is a nummulitic limestone; both here and near See also:Interlaken, in the See also:marble of Ralligstocke, calcareous See also:algae are abundant . Part of the " schistes See also:des See also:Grisons " (" Biindner Schiefer ") have been regarded as of Oligocene age . In the Leman region the " Flysch See also:rouge " at the See also: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 See also:Magdeburg and Latdorf near See also:Bernburg; at See also:Samland the glauconitic sand contains nodules of See also:amber, with insects, derived from Eocene strata . The upper Oligocene beds, which See also:cover a wide See also:area, comprise the See also:Stettin sands and Septarian Clay or Rupelton, marine beds tending to See also:merge laterally one into another . In the See also:Mainz basin a See also:petroleum-bearing sandy marl is found at Pechelbronn and Lobsann in Alsace underlying a fresh-water limestone which is followed by the marine Meeressand " of See also:Alzey . Lignites (Braunkohl) are widely spread in this region and appear at Latdorf, See also:Leipzig, in See also:Westphalia and See also:Mecklenburg; at See also:Halle is a variety called pyropissite, which is exploited at See also:Weissenfels for the manufacture of See also:paraffin . Map of Europe in the See also:early part of the Oligocene Period MS . =Lando, undifferentlated area See also:Lagoon.)areaa molasse " is usually given; mixed with the molasse is an inconstant conglomeratic littoral formation, called Nagelfluh . The molasse occurs also in See also:Bavaria, where it is several thousand feet thick and contains lignites . Oligocene deposits occur in the Carpathian region and See also:Tirol; as Flysch and brackish and lacustrine beds with lignite in Klausenburg, lignites at Haring in Tirol . In the See also:Spanish Pyrenees they are well See also:developed; in the See also:Apennines the scaly clays (" argille scagliose ") are of this age; while in See also:Calabria they are represented by thick conglomerates and Flysch . Flysch appears also in See also:Dalmatia and See also:Istria (where it is called " tassello ") and in North Bosnia, where it contains marine limestones . Lignites are found at Sotzka and See also:Styria, marine beds in the See also:Balkan See also:peninsula, glauconitic sands prevail in So' ith Russia, Flysch with sands and grits in the See also:Caucasus, while 'marine deposits also occupy the Aral-Caspian region and See also:Armenia, and are to be traced into See also:Persia . Oligocene rocks are known in North See also:Africa, See also:Algeria, See also:Tunis and See also:Egypt, with the silicified trees and See also:basalt sheets north of the See also:Fayum . In North See also:America the rocks of this period have not been very clearly differentiated, but they may possibly be represented by the White See also:river beds of S . Dakota, the white and blue marls of See also:Jackson on the See also:Mississippi, the " Jacksonian " white limestone of See also:Alabama, the limestone of See also:Ocala in See also:Florida, certain lacustrine clays in the Uinta basin, and by the See also:rib-See also:band shales with See also:asphalt and petroleum in the coastal range of See also:California . In South America and the See also:Antilles upper Oligocene is found, and the lignite beds of Coronet and Lota in See also:Chile and in the Straits of See also:Magellan may be of this age; in See also:Patagonia are the lower Oligocene marine beds (" Patagonian ") and beds with mammalian remains . In New See also:Zealand the See also:Oamaru series of J . See also:Hutton is regarded as Oligocene; at its See also: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) . See also:Corals were abundant, and nummulites still continued till near the close of the period, but they were diminished in See also:size . |
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