Paleogene System Period
Paleogene System (Period)
the first system of the Cenozoic erathem, corresponding to the first period of the Ceno-zoic era of the earth’s geologic history. The Paleogene follows the Cretaceous and precedes the Neogene system. The name Paleogene system was suggested in 1866 by the German geologist K. Naumann. Stratigraphic study of the Paleogene began in the vicinity of Paris, where local stages were identified and their facies, paleogeography, and fauna were determined. The absolute age of the lower (68 ± 2 million years) and upper (25 ± 2 million years) boundaries of the Paleogene system have been calculated by radiogeological methods.
In what is now the USSR, Paleogene deposits have been studied by the Russian and Soviet geologists A. P. Pavlov, A. V. Nechaev, A. D. Arkhangel’skii, N. A. Sokolov, I. M. Gubkin, and others. Important contributions to the study of the Paleogene were also made by O. S. Vialov, I. A. Korobkov, M. V. Muratov, and A. L. Ianshin. Paleontological substantiation for the Paleogene was provided by V. V. Menner, R. L. Merklin, A. A. Borisiak, A. N. Krishtofovich, I. M. Pokrovskaia, and many others. Abroad, the Paleogene system has been studied by numerous scientists, including the Frenchmen A. d’Orbigny, A. Dumont, A. Lapparent, R. Abrard, and M. Kosman; the Italians R. Fabiani and F. Sacco; the Englishman J. Prestwich; the Swiss G. M. Bolli; the Americans W. Clark, C. V. Weaver, and V. Mallory; the Japanese K. Hatai and M. Yokoyama; and the New Zealander G. Finley.
Subdivisions. Paleogene deposits are subdivided into three series—Paleocene, Eocene, and Oligocene. Further division into stages and zones is local. In the USSR a local scale of Paleogene stages has been constructed. For this purpose, a continuous section of the Paleocene and Eocene in the Crimea was chosen; each part of the section is characterized by various groups of fauna, such as mollusks, large and small foraminifers, bryozoans, and sea urchins. Distinct stages have been identified in the stratotype. The Oligocene has not yet been studied to the same degree. Soviet geologists have worked out detailed stratigraphic schemata for certain areas of distribution of Paleogene deposits (see Figure 1).
General description. Large-scale tectonic movements occurred
in the Paleogene period. In the western part of North and South America the mountain structures of the Cordilleras and Andes continued growing until the Eocene in the north and until the Oligocene in the south. Thick volcanogenic and terrigenous strata of both marine and continental origin accumulated in the adjacent peidmont troughs. Between Europe and Africa and in the southern half of Asia, a large geosynclinal system stretched from the present-day Pyrenees to Burma. In the second half of the Paleogene period folding and orogeny occurred in various parts of the system, and there resulted two chains of mountainous islands enveloping the Mediterranean Sea on the south and north. Along the eastern margin of Africa a meridional system of large grabens, the Great Rift Valley, arose during the Paleogene. Flows of basaltic magma occurred along the faults bordering the graben system. The development of the Pacific geosynclinal belt continued in the Far East. In addition to the regions mentioned above, evidence of volcanism has been observed in Asia Minor, on the Balkan Peninsula, in Greenland, in Japan, and in the USSR (Transcaucasia, the Badkhyz, the northeast, Kamchatka, and Primor’e).
The Paleogene transgression developed at many points in the northern hemisphere and reached a maximum by the end of the Eocene. By this time, the sea had flooded the southern half of the Eastern European Platform, the Turanian and Western Siberian plates, Transcaucasia, Central and Southern Europe, northern Africa, and other regions. Tectonic movements that occurred in the early Oligocene caused a regression of the sea; exceptions included Central Europe, the Caribbean Sea, and the Gulf of Mexico. The Oligocene was characterized by an intensification of the continental nature of the climate. Flysch formation occurred in the geosynclinal basins; marine molasses began forming in the Oligocene. In the basins of the Mediterranean region massive nummulitic and lepidocyclin limestones typical of the Paleogene accumulated. Carbonate silts, greensand, quartz sands, opokas, tripolites, spongolites, and clays were deposited on the platforms. Dark clays with concretions of marl, dolomite, and ankerite, as exemplified by the Maikop series, were widespread in Oligocene basins. Carbonate and, more rarely, terrigenous silts accumulated on the floor of the Atlantic, Pacific, and Indian oceans. Coal-bearing sediments and red clays developed extensively among the continental deposits.
The organic world. The land fauna of the Paleogene differed sharply from the fauna of the Cretaceous. By the beginning of the Paleogene many groups of reptiles—dinosaurs, pterosaurs, and such marine reptiles as ichthyosaurs and plesiosaurs—had become extinct. The groups of amphibians typical of the Holo-cene existed. Teleosts were the most important fish of the time. Mammals became widespread during the Paleogene. In the Paleocene they were represented by primitive forms, but with the Eocene there appeared Insectivora, Rodentia, Primates, Carnivora, Ungulata, Proboscidea, Cetacea, and Sirenia. In most cases, these orders were represented by families that later became extinct.
The plant kingdom of the Paleogene was dominated by angiosperms. The gymnosperms were the second most important group. During the Paleogene the flora underwent considerable evolution. The flora has been studied not only through leaf imprints and large plant fragments but also in more detail through the use of pollen and spores. In the Paleocene and Lower Eocene considerable development was achieved by angiosperms that were different from the present-day taxa and that subsequently became extinct. Representatives of present-day genera of plants appeared in the Middle Eocene and reached their maximum development in the Oligocene.
Miospores and the remains of marine plankton organisms— such as pelagic foraminifers, nannoplankton, radiolarians, and diatoms—play the most important role in the subdivision and correlation of Paleogene sections.
Biogeographic regionalization. The outlines of the modern zoogeographic provinces took shape in the Paleogene. A distinctive fauna of marsupials and monotremes developed in Australia from the late Cretaceous. In the early Eocene, South America became separate, and a fauna of marsupials, edentates, ungulates, and long-tailed monkeys developed there.
The marine fauna of the Paleogene was typified by the num-mulites, large foraminifers that reached 10–12 cm. French geologists even called the Paleogene the Nummulitic system. Small foraminifers and radiolarians were also quite common. Worms, sponges, bivalve and gastropod mollusks, ostracods, sea urchins, sea lilies, and bryozoans became widespread, as did brachiopods and corals in the warm seas. The Atlantic and Pacific zoogeographic provinces took shape with respect to marine fauna.
Two types of flora have been established for the early Paleogene of the northern hemisphere on the basis of miospores. Nor-mapolles types predominate to the west of the Enisei River valley, and Aquilapollenites flora to the east of the Enisei. Latitudinal zonation, however, was very important. Two floristic provinces have been identified in the northern hemisphere. The northern, or Greenland, province included Siberia, the Far East, the United States, Greenland, and Spitsbergen, and was characterized by the development of deciduous broadleaf plants. The southern province included Western Europe, the Ukraine, the Caucasus, Kazakhstan, southern Asia, and Mexico and was characterized by hygrophilous tropical vegetation; this vegetation, which included palms, laurels, bamboo, and ferns, became xerophytic in the Oligocene. As the climate grew steadily cooler in the Oligocene, the climatic latitudinal zonation became more distinct. By the end of the Oligocene gramineous vegetation had become widespread in the southern regions of the USSR for the first time. Diatoms and coccolithophorids developed extensively in the seas of the Paleogene (the Ukraine, the Volga Region, and Western Siberia).
Paleogene deposits in the USSR. Paleogene sediments are widespread in the USSR and are represented in both marine and continental facies. Flysch developed in the Carpathians; above it there is a thick stratum of “menelite” clays of Oligocene age. On the Ukrainian plain, in the southern part of Byelorussia, in Lithuania, in the Lower and Middle Volga Region, in Ciscaucasia, and in the north Caspian region, marine formations of the Paleogene system are known. These formations are marily terrigenous and siliceous, and they partially outcrop in places. Some horizons—for example, the Simferopol’ nummulitic limestones and the Alma limestones—are composed of carbonate rocks. Continental sands are known in the Ukrainian crystalline shield, in the Baltic syneclise, in the Dnieper-Donets Basin and to the west of the Urals. The Paleogene deposits in the Caucasus are distinguished by variegation of facies. Flysch and the black clays of the Oligocene (Maikop stratum) are extensively developed, as are volcanogenic formations in Transcaucasia. Paleogene deposits are common in Middle Asia and Kazakhstan. Marine terrigenous and carbonate series are developed in Mangyshlak, the Ustiurt, the Kopetdag, the Karakums, the Kyzylkum, the northern Aral region, and the Fergana and Tadzhik depressions; in the Badkhyz the series are associated with volcanogenic formations. Beginning with the late Eocene, continental, primarily terrigenous sediments became widespread in such areas as the Tadzhik, Fergana, Chu-Ili, and Zaisan depressions and the Turgai Trough. In Western Siberia the Paleocene and Eocene are composed of marine series (terrigenous sediments rich in SiO2); in the Oligocene, alluvial, marsh, and lacustrine sands and clays were deposited in the eastern part of the Western Siberian Plain. East of the Enisei the Paleogene system is represented by continental sediments that in a few places have been preserved from erosion. On the Siberian Platform the sediments are known in the Angara and Anabar basins and in the Enisei Ridge. Alluvial formations (Selenga River) are well developed in the Baikal Region. Coal-bearing Paleogene deposits have been found in the basins of Yakutia and the Altai-Saian region, in a number of basins of the Far East, in the Kolyma Lowland, and on the Novosibirskie Islands. A covering detrital shingle of the Paleogene is well developed on the divides of the Lena delta, the northeastern USSR, and elsewhere. Volcanogenic Paleogene series, sometimes reaching considerable thickness, are developed extensively in Sikhote-Alin’, the northeastern USSR (for example, the Omolon Upland), and among the marine deposits of the Paleogene in the Koriak Mountains, Kamchatka, and the Komandorskie and Kuril islands. Marine terrigenous deposits of the Paleogene system are known to the east of the Western Siberian Plain on the Novosibirskie Islands, in the Koriak Mountains (the Anadyr’-Penzhina Depression), on Kamachat-ka, and on Sakhalin, where they alternate with continental deposits.
Minerals. The deposits of the Paleogene are rich in minerals. Deposits of brown coal are found in the European USSR, Transcaucasia, the Far East, and other regions of the USSR; abroad, they are in the German Democratic Republic, the Federal Republic of Germany, the United States, and Canada. There are oil and gas deposits in the Carpathians, the Caucasus, Ciscaucasia, Middle Asia, the Middle East, Alsace, California, Venezuela and elsewhere. Bituminous shales are very important in the Carpathians, Crimea, Caucasus, and Middle Asia. Unique deposits of amber in the Baltic Region and also in the Dnieper-Donets Depression are associated with the Paleogene system. Phosphorites have been found in the Dnieper-Donets Depression, the Volga Region, and the Turgai Trough in the USSR; abroad, they have been discovered in such areas as Tunisia, Algeria, and Morocco. In the USSR deposits of manganese are associated with Oligocene deposits in the Ukraine, Tanscaucasia, and Mangyshlak. Sedimentary iron ores are found in the Turgai Trough, the Western Siberian Plain, and the Zaisan Depression. Other deposits associated with the Paleogene include bauxites (in the Ukraine and Kazakhstan of the USSR and in the United States and India abroad), diatomites (the Volga Region and Western Siberia), and potassium salts (Alsace and Spain).
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Gignoux, M. Stratigraficheskaia geologiia. Moscow, 1952. (Translated from French.)
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Schuchert, C. Paleogeograficheskii atlas Severnoi Ameriki. Moscow, 1957. (Translated from English.)
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V. A. GROSSGEIM