Formation(redirected from chiasma formation)
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the basic unit of local stratigraphic subdivisions, composed of strata of sedimentary, igneous, or metamorphic rocks, sometimes homogeneous in composition but other times represented by an alternation of different types of rocks. Formations have their own geographic names, are joined into series, and are subdivided into members and bands. A formation is principally defined by its lithological composition, which is homogeneous throughout the formation. Some formations are defined by the presence of animal and plant fossils. The age of a formation is relatively uniform throughout the distribution, although the boundaries may shift somewhat in time. The term “formation” as understood by American geologists is essentially a synonym of the Russian term svita but allows a much greater spread in time.
REFERENCESStratigraficheskaia klassifikatsiia, terminologiia i nomenklatura. Leningrad, 1965.
Dunbar, C, and J. Rodgers. Osnovy stratigrafii. Moscow, 1962. (Translated from English.)
a disposition of military personnel, subunits, or units established by regulations for the coordination of operations. A formation promotes stronger military discipline and ensures rapid, organized troop movements and control of troops.
Formations usually consist of rows of men or lines of vehicles, in which the men or vehicles are arranged in a single line at set intervals on either side and in front and back. The direction that the men or vehicles face is the front of the formation; the opposite of the front is the rear. The right and left sides of the formation are the flanks; when formations turn, the designations of the flanks do not change. The distance between flanks is the width of the formation, and the distance from the first to the last row is the depth of the formation.
Depending on the number of rows, a formation may be singleranked or double-ranked; in the latter, the men in the second row are arranged at a distance of one pace to the rear of the men in the first row. In addition to these types of formations, the column is also used. In a column, the men are arranged behind one another, and units or vehicles follow each other. Columns and ranks are used in the disposition of subunits and units in deployed or march formations. In deployed formations, subunits are disposed on a single line along the front in single-rank or doublerank formation or in a line of columns at intervals established by the Drill Manual or the commander’s order. In march formations, units are disposed in columns.
in geology, a natural assemblage of rocks, minerals, and ores that are paragenetically related and that are of similar age and geological origin.
The concept of the formation arose in the 18th century to designate large strata of sedimentary rocks identified by the predominance of certain rock types or combination of types and by position in the general sequence of geological bedding, for example, chalk and the Old Red Sandstone in Europe. The term later lost its stratigraphic meaning, especially in Russian and Soviet geology, and took on a genetic or paragenetic meaning; only in the American literature is the term “formation” used to designate subdivisions of regional lithostratigraphic scales, in a sense approximately corresponding to the Russian term svita (“series”). The French geologist M. Bertrand in 1897 considered formations to be rock facies, such as flysch and molasse, representing distinct stages in the development of geosynclines.
The concept of the formation has been supplied to magmatic rocks (F. Iu. Levinson-Lessing, Iu. A. Kuznetsov, F. Turner, J. Verhoogen), metamorphic rocks (A. A. Marakushev, N. L. Dobretsov, V. S. Sobolev), and metasomatic rocks (D. S. Korzhinskii, V. A. Zharikov, B. I. Omel’ianenko).
Russian and Soviet researchers have made major contributions to the theory of the formation. In the work of V. V. Belousov, N. B. Vassoevich, A. B. Ronov, V. E. Khain, N. P. Kheraskov, and N. S. Shatskii, among others, the term “sedimentary formation” denotes a large, regularly recurring combination of specific rocks attesting to the stability of the conditions of rock development approximately corresponding in size to geological systems or series or their parts. Each formation is characterized by similar composition, structure, and distribution, which reflect its origin under certain paleogeographic conditions that predominated at a certain stage in the development of the particular tectonic province or zone with its characteristic tectonic conditions and climate. Formations are assemblages of facies and genetic types of deposits. The boundaries of a formation may alter in time; the characteristics of different types of formations, recurring in beds of different age, alter somewhat as well.
Formations are identified on the basis of the composition of rocks and are classified primarily according to the tectonic features with due regard for climatic conditions, which, in some cases, play a very important part. The three principal groups of formations—sedimentary, volcanic, and magmatic—are often found in distinct combinations. For example, volcanic and intrusive formations linked by common magma centers form what are called volcanic-plutonic associations, such as the trap association of plateau basalts, dolerites, and gabbro-diabases or the association of andesite-rhyolite volcanites and granitoids. Such associations may also form magmatic and sedimentary formations, for example, the ophiolite association of ultrabasic and basic intrusive rocks, basic lavas, and silica-carbonate abyssal sediments and the shale-diabase association of shales, spilites, and diabases.
Formations are combined in lateral (by area) or vertical series. The sequence of lateral formations corresponds to tectonic and climatic zonality; the vertical sequence matches the stages of development of individual major tectonic zones—platforms, eugeosynclines, miogeosynclines, and orogens [from which N. B. Vassoevich derived the term “geogeneration” (1940, 1966), which corresponds to the stage-zonal concept of formation or lithological association]. A typical example of a vertical series of sedimentary geosynclinal formations includes a slate formation, flyschmolasse, and so on. The type of tectonic structure can be determined from a formation, as well as the structure’s stage of development and the general climatic setting in the formative period.
The theory of magmatic formations is being successfully developed in the USSR by Iu. A. Kuznetsov as a special field of research on the boundary between tectonics and petrology. Magmatic formations are aggregates of magmatic rocks that occur in a distinct geological setting and correspond to distinct stages in the development of a particular segment of the earth’s crust.
The principle of the common origin of metamorphic rocks linked with specific tectonic structures (mobile belts or platforms) at different stages of their development also forms the basis for the identification of metamorphic formations. For example, metamorphic formations of spilites form in the early stages of the development of eugeosynclines, while in the concluding stages of geosynclines metamorphic formations of gneisses and migmatites form, as well as slates, shales, schists, and phyllites.
The concept of metasomatic formations, for example, skarn, greisen, and albite formations, is not as well developed; by a number of characteristics, such formations should be classified as secondary formations. Closely linked and associated with magmatic and metasomatic formations are ore formations, which are groups of ore deposits of mineral raw material of similar composition formed under similar geological and physicochemical conditions at the earth’s surface or within the earth’s interior. Examples of ore formations are the chromite and pyrrhotitechalcopyrite-pentlandite formations. The theory of ore formations is developing as a special branch of the science of ore deposits (A. G. Betekhtin, Iu. A. Bilibin, I. G. Magak’ian, R. M. Konstantinov, V. A. Kuznetsov, and V. I. Smirnov).
Certain types of mineral products are linked to certain formations, which makes formation analysis very important not only in lithology, paleogeography, and tectonics but also for ascertaining the regularities in the distribution of various minerals and developing the appropriate scientific foundations for prospecting.
REFERENCESShatskii, N. S. Izbr. tr., vol. 3. Moscow, 1965.
Vassoevich, N. B. “Istoriia predstavlenii o geologicheskikh formatsiiakh (geogeneratsiiakh).” Osadochnye i vulkanogennye formatsii. Leningrad, 1966. (Tr. Vses. n.-i. geol. in-ta: Novaiaseriia, vol. 128.)
Kuznetsov, Iu. A. Glavnye tipy magmaticheskikh formatsii. Moscow, 1964.
Kheraskov, N. P. Tektonika i formatsii. Moscow, 1967.
Magak’ian, I. G. Tipy rudnykh provintsii i rudnykh formatsii SSSR. Moscow, 1969.
Problemy magmaticheskoi geologii. Novosibirsk, 1973. (Tr. In-ta geologii i geofiziki, issue 213.)
Marakushev, A. A. Petrologiia metamorficheskikh gornykh porod. Moscow, 1973.
V. E. KHAIN
i. When the flight leader has requested and ATC (air traffic control) has approved other than standard formation dimensions.
ii. When operating within an authorized altitude reservation (ALTRV) or under the provisions of a letter of agreement.
iii. When the operations are conducted in airspace specifically designed for a special activity. The formation normally operates as a single aircraft with regard to navigation and position reports.