Carboniferous System Period

the fifth system of the Paleozoic group, corresponding to the fifth period of the Paleozoic era of earth history.

It has been established by radio geological methods that the Carboniferous period began 350 million years ago; it was 65–75 million years long. The Carboniferous period followed the Devonian and preceded the Permian period. The Carboniferous system was distinguished in 1822 by W. Conybeare and W. Phillips in Great Britain. In Russia the Carboniferous system and its fossil flora and fauna were studied by such scientists as V. I. Meller, S. N. Nikitin, and F. N. Chernyshev and in the Soviet period by M. D. Zalesskii, A. P. Ivanov, E. A.Ivanov, D. V. Nalivkin, M. S. Shvetsov, M. E. Ianishevskii, L. S. Librovich, S. V. Semikhatova, D. M. Rauzer-Chernousova, A. P. Rotai, V. E. Ruzhentsev, and O. L. Einor. In Western Europe the most important research has been done by the English scientist A. Vaudhan and the German paleobotanist W. Gothan. In North America the principal investigators include C. Schuchert and C. Dunbar.

Subdivisions. In the USSR and certain other countries (China, Japan) the Carboniferous system is divided into three parts. In Western Europe a two-part division is customary; in this case the upper division corresponds not only to the middle and upper divisions accepted in the USSR but also to the top part of the lower division (the Namurian stage). In the United States the lower division of the Carboniferous system in its Western European definition (including the lower part of the Namurian stage) is considered an independent system, the Mississippian, while the upper division is termed the Pennsylvanian system. (See Figure 1.)

There is no international breakdown of the stages of the Carboniferous system into zones. A breakdown into zones is used only for the lower division in Western Europe and the marine deposits of the USSR.

General description. The deposits of the Carboniferous system are found on all continents. The classical sections are in Western Europe (Great Britain, Belgium, and the Federal Republic of Germany), Eastern Europe (the Donbas, the Moscow syneclise), and North America (the Appalachians and the Mississippi River basin, for example). The mutual arrangement of platforms and geosynclines in the Carboniferous period remained the same as it had been during the Devonian period.

On the platforms of the northern hemisphere the Carboniferous period is represented by marine deposits (limestone, sand-clay sediments that are often coal-bearing). In the southern hemisphere, continental deposits—detrital and glacial (frequently

tillites)—are most common. Lava sheets, tuffs and tuffites, siliceous coarse-fragmented sediments, and flysch are also found in the geosynclines.

By the nature of geological processes and the paleogeographic situation the Carboniferous period is divided into two stages almost everywhere in the world; the first of them covers the early Carboniferous, while the second covers the middle and late parts. After the early Carboniferous, as a result of the Hercynian folding; marine conditions over vast areas of the middle Paleozoic geosynclines were replaced by continental conditions. In some places in Southeast Asia and the Eastern European and North American platforms, seas engulfed land sectors that had only recently risen. The Carboniferous is one of the thalasso-cratic periods; vast areas within the boundaries of the present continents were covered by the sea. Subsidences and the transgressions caused by them occurred more than once during the Carboniferous period. The greatest transgressions occurred in the first half of the period. During the early Carboniferous the sea covered Europe (with the exception of Scandinavia and the adjacent regions), a large part of Asia, North America, the extreme western part of South America, northwestern Africa, and the eastern part of Australia. The seas were shallow for the most part and had many islands. The largest single land mass was Gondwana. A markedly smaller land mass stretched from Scandinavia through the northern part of the Atlantic, Greenland, and North America. The central part of Siberia between the Lena and Enisei rivers and Mongolia and the Laptev Sea was also land. By the middle Carboniferous the sea had receded from almost all of Western Europe, the Western Siberian Lowland, Kazakhstan, Central Siberia, and other regions.

In the second half of the Carboniferous period mountain ranges were uplifted in the zones of Hercynian orogenesis (the Tien-Shan, Kazakhstan, the Urals, the northernwestern part of Europe, eastern Asia, and North America).

The climate of the continents was varied and changed from stage to stage. A common feature was the high humidity of the tropical, subtropical, and temperate belts, which promoted the spread of forest and swamp vegetation on all the continents. The accumulation of plant remains, primarily in peat bogs, led to the formation of numerous coal basins and deposits.

It is conventional to distinguish the following phytogeo-graphic regions: Euramerican or Westphalian (tropical and subtropical), Angara or Tunguska (nontropical), and Gondwanian (temperate climate). The climate of the Euramerican region became drier and subarid in places toward the end of the Carboniferous period. Other regions preserved their high humidity not only until the end of the Carboniferous but also during the Permian period. The greatest humidity and optimal conditions for peat accumulation (coal accumulation) in the Euramerican region were as follows: in the Greater Donbas at the end of the early Carboniferous and in the middle Carboniferous, in Western Europe in the Namurian and Westphalian, in North America in the middle and upper Carboniferous, and in Kazakhstan in the late Visean and the middle Carboniferous. In the southern part of the Angara region (the Kuznetsk Basin and other basins) the peat bogs grew intensively beginning the middle Carboniferous; in Gondwana this growth occurred from the late Carboniferous until the end of the Permian period. Only a limited territory had a dry climate during the Carboniferous. For example, during the Tournaisian age one of the arid climate zones stretched from southern Kazakhstan through the Tien-Shan to the Tarim massif. The basins distinguished by dry climate in this age stretched from Kazakhstan to the Siberian highlands and lower reaches of the Lena River. Marked and long-lasting aridization of the climate came in the Bashkirian age and continued until the Permian and Triassic in Kazakhstan, in the region from the Turgai to the Teniz and Dzhezkazgan basins; copper ores formed in these areas.

In the Tournaisian age the equator ran (according to the paleomagnetic data of A. N. Khramov) through the Black Sea and the Scandinavian peninsula; from the Visean age until the late Carboniferous it extended from the Balkan peninsula toward northwestern Europe. In the middle and late Carboniferous the north pole was evidently located north of the mouth of the Lena River. Marked climatic contrasts among different belts developed beginning in the middle and late Carboniferous. Beginning in the middle Carboniferous the part of USSR territory east of a line from Lake Balkhash to the mouth of the Enisei River differed from the part west of the line by its temperate climate. This is indicated by the nature of the flora and marine fauna. Only the Sikhote-Alin’, like virtually all non-Soviet Asia (with the exception of Mongolia), belonged to the belt of tropical and subtropical climates. On the continent of Gondwana (in Australia and Antarctica), during the middle and late Carboniferous, a climate that promoted glaciation occurred periodically.

Magmatic activity manifested itself in the form of eruptions and intrusions in the Uralian, Tien-Shan, Kazakhstan, and Mongolian-Okhotsk geosynclines, as well as in many others in Western Europe, non-Soviet Asia, North and South America, and eastern Australia. The Carboniferous period was one of the periods of greatest magmatic (especially intrusive) activity, which was closely related to the apogee of Hercynian orogenesis.

The organic world. At the very beginning of the period the predominant flora included small-leaved Lycopsida (Lepidoden-dropsis and Sublepidodendron, for example), fern-like gymno-sperms (pteridosperms), primitive articulated stem plants, and Pteropsida (primarily protoferns). Even in the early Carboniferous the primitive Lycopsida were replaced by large treelike Lepidodendron and Sigillaria, which were especially common in the middle Carboniferous. In the tropics (the Euramerican region) during the middle Carboniferous there prevailed forests consisting of high-trunked Lycopsida with large numbers of pteridosperms (Neuropteris, Mariopteris, Alethopteris) and other ferns, calamites, and Sphenopsida. To the north (the Angara region) during the early Carboniferous the Lycopsida predominated, and in the middle and late Carboniferous the cordaites and pteridophytes prevailed. It appears that at this time the glossopterian flora especially characteristic of the Permian had already developed in the Gondwana region. In phytogeographic regions with temperate climates there was a comparatively gradual development of flora from the middle Carboniferous to the early Permian. In the tropics during the late Carboniferous, on the contrary, there was a radical change in the vegetation of swampy lowlands in some places owing to aridization of the climate. The principal plant groups became the pteridosperms and treelike ferns. Conifers spread in the elevated areas.

The seas of the Carboniferous abounded in blue-green algae (Beresella, Ungarella, Donezella), while fresh waters had green coal-forming algae (Pila, Reinschia).

The animal world of the Carboniferous was extremely varied. In the seas the foraminifera were very common and underwent rapid evolutionary changes during the Carboniferous, producing dozens of genera and thousands of species. For stratigraphy the most important are the superfamily Fusulinidae: Eostajfela in the Lower Carboniferous; the genera Fusulina, Fusulinella, and others in the Middle Carboniferous; and Triticites and others in the Upper Carboniferous. Among the coelenterates the tetracor-als continued to dominate (Caninia, Dibunophyllum, Lithostro-tion) along with the tabulate corals (Syringopora, for example) and the stromatoporoids. There were various mollusks (bivalves, gastropods), rapidly evolved ammonoid cephalopods (various species of Goniatites and Eumorphoceras in the lower Carboniferous, Gastrioceras in the Middle Carboniferous, Uddenites and others in the Upper Carboniferous), which are especially important for comparing sections from places that are far away from each other, and nautiloids. Some bivalves (Carbonicola and Anthracomya, for example) inhabited strongly freshened lagoons and deltas, which permits them to be used for the stratigraphy of coal-bearing strata. Brachiopods, especially the orders Pro-ductida and Spiriferida, were common in the shallow seas. In the early Carboniferous (the Visean age) in the Moscow region, the Urals, and the Tien-Shan there were abundant large thick-shelled Gigantoproductus, strongly variable Striatifera that lived in banks, and others; in the middle and late Carboniferous numerous species of the Choristites genus were widespread. Some sectors of the sea floor were especially favorable for the development of bryozoans; representatives of the Fenestellidae family (genera Polypora, Fenestella, and Archimedes) were prevalent. There were various arthropods. Trilobites continued to exist, although in small numbers. There were many different groups of ostracods. Among the Echinodermata the crinoids developed abundantly; their segments make up whole layers in the limestone beds. Fossils of sea urchin are common in some places, while blastoids are rare.

Various classes of vertebrates, especially fish (marine and freshwater) underwent significant evolutionary changes. Bony fish and sharklike fish (Cladodus and Stenacanthus, for example) developed. On land the amphibians (stegocephalians) were dominant; reptiles were still rare. Fossils of numerous insects have been found (mayflies, dragon flies, Dictyoptera), some of them of gigantic size.

Biogeographic regionalization. The phytogeographic areas of Angara or Tunguska (Siberia, eastern Kazakhstan, and Mongolia) and the Euramerican (North America, Europe, North Africa, Anatolia, the Caucasus, central Kazakhstan, Middle Asia, China, and Southeast Asia) began to differentiate in the early Carboniferous; separation of the Gondwana region (South America, southern Africa, India, Australia, and Antarctica) took place at the end of the early Carboniferous, and during the late Carboniferous the formation of the Catasian region (China and Southeast Asia) from the Euramerican region took place. All charts of zoogeographic regionalization show a northern nontropical region (northern Asia and part of the arctic), a southern nontropical region (Australia and part of South America), and the tropical region lying between them, which included Tethys. Several provinces are identified within these regions (which are given different names).

Deposits in the USSR. Among the widespread Carboniferous deposits in the USSR two basic types of sections and formations are distinguished: platform and geosynclinal. The platform type is found on the Eastern European Platform and in the Tunguska Basin in Eastern Siberia. The geosynclinal type is found in the Donbas, the Caucasus, the Urals, the Tien-Shan, and Kazakhstan.

The section of the Carboniferous in the Donbas is classical in completeness, excellent exposure, and abundance and variety of paleontological remains. The Lower Carboniferous there is represented by limestones, while the Middle and Upper Carboniferous are represented by a thick (6–12 km) coal-bearing stratum: alternating layers of clay rock, sandstones, limestones, and coal beds. The shallow Carboniferous sections on the Eastern European Platform and the varied types of strata of all three subdivisions of the Carboniferous in the Urals, Tien-Shan, Kazakhstan, the Altai, the Kuznetsk Basin, the Tunguska Basin, the Verkhoiansk Range, and the Transbaikal region are interesting. Overlaid by younger deposits, Carboniferous deposits cover the entire central and eastern parts of the Eastern European Platform (and the Dnieper-Donets basin), a significant part of the Western Siberian and Turanian plates (plity), large areas in the Tunguska Basin, and territory east of the Lena River. Strato-types of the Moscovian and Gzhelian stages are found in the Moscow syneclise, and the stratotype of the Bashkirian stage is found in the Urals.

Minerals. Hard and brown coals form a series of basins and deposits on all continents and are limited to Hercynian foredeeps and internal basins. Basins in the USSR include the Donets (hard coals), Moscow (brown coals), Karaganda (hard coals), and Kuznetsk and Tunguska (coals of the Carboniferous and Permian systems). In addition there are deposits in the Ukraine, the Urals, central Caucasus, and elsewhere. In Central and Western Europe there are basins and deposits in Poland (Silesia), the German Democratic Republic and Federal Republic of Germany (Ruhr), Belgium, the Netherlands, France, and Great Britain. In the United States there are the Pennsylvanian and other basins. Many petroleum and gas deposits date to the Carboniferous (Volga-Ural region, the Dnieper-Donets basin). Also known are numerous deposits of iron ore, manganese, copper (the largest is Dzhezkazgan), lead, zinc, aluminum (bauxite), and refractory and ceramic clays.