Facies(redirected from masked facies)
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in phytocenology, a taxonomic category having various meanings. The term is often used to designate geographic variants of an association that have a somewhat different floristic composition than the basic association yet have the same dominants (V. V. Alekhin). Facies is also the designation for geographic variants of an association that arise on the site where the indigenous vegetation has been destroyed (S. I. Korzhinskii). Taxonomic units that are larger than formations are also referred to as facies, for example, all coniferous forests (Soviet geobotanist B. A. Bykov). The term is used in the classification of forests in reference to an intermediate taxonomic unit between formation and group (B. P. Kolesnikov). In Western Europe the term “facies” is used by the school of the Swiss geobotanist Braun-Blanquet to designate the smallest taxonomic unit isolated within an association on the basis of the predominance of a certain species or of certain species; it corresponds somewhat to the term “sociation.”
The term “facies” is sometimes used in a sense closely related to biogeocenosis (L. S. Berg and L. G. Ramenskii) or to designate groups of homogeneous biogeocenoses (V. B. Sochava). The terms “fasciation” and “facies” are used by American botanists to designate the stage of formation of phytocenoses with primary and secondary successions.
T. A. RABOTNOV
in stratigraphy, a concept that originated in the 19th century to express changes in the lithologic composition of rocks and embedded organic remains within a stratigraphic unit over the areal extent of the unit. The term “facies” was suggested by the Swiss geologist A. Gressly between 1838 and 1841. Gressly associated the origin of facies changes with differences in the conditions of rock formation and compared the facies changes to the changes that can be observed on the present-day sea floor. Therefore, he grouped and named the facies according to the environment in which the rocks accumulated, for example, littoral and pelagic facies.
In Russian geological literature, the term “facies” in Gressly’s sense was first used in 1868 by N. A. Golovkinskii to designate changes in the Permian deposits of the Volga and Kama river basins. Gressly’s concept of facies was multifaceted, encompassing the petrologic composition of rocks, the organic remains embedded in rocks, the origin of deposits, and changes in deposits within a specific stratigraphic framework. As a result, the term “facies” was later used in different senses. The term is most widely used to designate the physicogeographical conditions under which ancient sediments accumulated, together with all environmental characteristics, such as the environment’s dynamics, chemical conditions, life-forms, and depth; it has been used in this sense by, for example, N. M. Strakhov (1948), D. V. Nalivkin (1955), V. E. Khain (1973), and N. V. Logvinenko (1974).
Because the physicogeographical conditions are established on the basis of preserved features of the rocks and embedded fossils, the term “facies” can have either of the two following meanings: (1) the rock that occurs in a specific environment or (2) the environment in which recent or ancient sediments accumulated and which may be inferred from the sediment or rock. These two definitions are very similar and complement each other.
Facies often designate the conditions that prevailed in different stages of lithogenesis. For example, weathering facies are identified when the weathering stage is studied, diagenetic facies are identified when the stage in which sediment is transformed into rock is studied, and epigenetic facies are identified when subsequent transformations of sedimentary rocks that have already formed are studied. The Finnish geologist P. Eskola introduced the concept of metamorphic facies, applicable to metamorphic rocks. The term “facies” is widely used to designate particular characteristics of the recent and ancient environments in which sediment accumulated and to designate various features of the sediments and rocks.
In 1933, L. V. Pustovalov introduced the concept of fossil geo-chemical facies, which constitute a stratum or suite of strata and which, throughout their extent, have an identical geochemical characteristic that was imparted during rock formation. The term “geochemical facies” is widely accepted among petroleum geologists because it indicates the geochemical characteristics of the environment in which sediments accumulated and of diagenesis, which are important for the accumulation of the organic matter from which petroleum originates.
American geologists F. Pettijohn, L. Sloss, and W. Krumbein introduced the concept of lithofacies, which signify the common characteristics of the lithologic composition of rocks of a specific stratigraphic unit in a given region. Examples include arenaceous and argillaceous facies. Lithofacies may also include facies identified according to minerals, rock textures, or rock structures. The concept of lithofacies is used especially often in articles on petroleum geology. Biologic facies, or biofacies, are also distinguished. Such facies are fossil biocenoses reconstructed according to preserved organic remains; examples include coralline and graptolitic facies.
Thus, facies are distinguished according to the environment in which sediments accumulated, the composition of sediments, the stages of rock alteration, or organic remains. Less often, facies are distinguished according to other features. For example, physiofacies are based on the physical state of the environment and include warm-water and subaerial facies; tectofacies are based on tectonic characteristics and include geosynclinal, shelf, and fore-deep facies.
The term “facies” is also taken to mean beds whose composition and physicogeographical conditions of formation differ from those of neighboring beds of the same stratigraphic interval, which may vary in areal extent. This meaning has been used by N. S. Shatskii (1955), G. F. Krasheninnikov (1971), and G. P. Leonov (1974). In this approach, a facies is considered a geologic body whose composition and formation conditions differ from those of adjacent beds of the same age. This important restriction applies to both fossil and recent facies.
The branch of geology that considers the physicogeographical environments in which sedimentary rocks formed is called the study of facies (D. V. Nalivkin). The procedures for reconstructing the environments for past periods in the earth’s history is called facies analysis (lu. A. Zhemchuzhnikov). Facies analysis is one of the principal methods of historical geology.
REFERENCESStrakhov, N. M. Osnovy istoricheskoi geologii, part 1. Moscow-Leningrad, 1948.
Nalivkin, D. V. Uchenie o fatsiiakh, vols. 1–2. Moscow-Leningrad, 1955–56.
Rukhin, L. B. Osnovy litologii, 3rd ed. Leningrad, 1969.
Krasheninnikov, G. F. Uchenie o fatsiiakh, Moscow, 1971.
Logvinenko, N. V. Petrografiia osadochnykh porod, 2nd ed. Moscow, 1974.
Leonov, G. P. Osnovy slratigrafii, vol. 2. Moscow, 1974.
G. F. KRASHENINNIKOV