Facies


Facies

:"The term "Facies" can also refer to distinctive facial expressions associated with conditions such as Williams syndrome."In geology, facies are a body of rock with specified characteristics. [Reading (1996)] Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment.

The term facies was introduced by the Swiss geologist Amanz Gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy, [Cross and Homewood (1997)] which replaced the earlier notions of Neptunism.

Facies types

edimentary facies

Generally, facies are distinguished by what aspect of the rock or sediment is being studied. Thus, facies based on petrological characters such as grain size and mineralogy are called lithofacies, whereas facies based on fossil content are called "biofacies".

These facies types are usually further subdivided, for examples, you might refer to a "tan, cross-bedded oolitic limestone facies" or a "shale facies". The characteristics of the rock unit come from the depositional environment and original composition. Sedimentary facies reflect depositional environment, each facies being a distinct kind of sediment for that area or environment.

Since its inception, the facies concept has been extended to related geological concepts. For example, characteristic associations of organic microfossils, and particulate organic material, in rocks or sediments, are called palynofacies. Discrete seismic units are similarly referred to as seismic facies.

Metamorphic facies

The sequence of minerals that develop during progressive metamorphism (that is, metamorphism at progressivley higher temperatures) define a "facies series" and depend on the pressure, or range of pressures, at which the progressive metamorphism occurred.

Walther's Law of Facies

Walther's Law of Facies, named after the geologist Johannes Walther, states that the vertical succession of facies reflects lateral changes in environment. Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another.(Stanley, 134) A classic example of this law is the vertical stratigraphic succession that typifies marine trangressions and regressions. However, the law is not applicable where the contact between different lithologies is non-conformable (i.e. sedimentation was not continuous), or in instances of rapid environmental change where non-adjacent environments may replace one another.

See also

* Lithofacies
* Metamorphic Rock
* Palynofacies
* Sequence stratigraphy
* Stratum

References

* Cross, T. A. and Homewood, P. W., (1997), Amanz Gressly's role in founding modern stratigraphy. "Geological Society of America Bulletin" 109 (12) 1617-1630.

* Reading, H. G. (Ed.), (1996), "Sedimentary Environments and Facies". Blackwell Scientific Publications. ISBN 0-632-03627-3

* Stanley, Steven M. "Earth System History". New York: W.H. Freeman and Company, 1999. ISBN 0-7167-2882-6


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  • faciès — [ fasjɛs ] n. m. VAR. (vx ou sc.) facies • 1823; bot. 1758; lat. facies « face » ♦ Didact. 1 ♦ Aspect du visage (en médecine, anthropologie). Le faciès indien, mongol. « Quelle admirable figure aura le père Babinet [...] Je vois de là son facies …   Encyclopédie Universelle

  • facies — faciès [ fasjɛs ] n. m. VAR. (vx ou sc.) facies • 1823; bot. 1758; lat. facies « face » ♦ Didact. 1 ♦ Aspect du visage (en médecine, anthropologie). Le faciès indien, mongol. « Quelle admirable figure aura le père Babinet [...] Je vois de là son… …   Encyclopédie Universelle

  • Facies — Faciès Sommaire 1 Sens commun 2 Signification en géologie 3 Signification en sédimentologie 4 Signification en biologie …   Wikipédia en Français

  • facies — FÁCIES, faciesuri, s.n. 1. Aspect caracteristic al feţei în cursul unei boli, al unei stări emotive etc.; p. gener. fizionomie. 2. Aspect al unei culturi arheologice în ce are ea mai caracteristic. 3. Totalitate a particularităţilor mineralogice… …   Dicționar Român

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  • FACIES — soli animalium est homini, cuius loco coeteris os et rostra, Plin. l. 11. c. 31. De ea sic Paschal. Coron. l. 5. c. 3. Ecquis non stupeat in illa altera (capitis parte) quae est attributa vultui, qui vultus est imago ingenii? Nam quia frons est… …   Hofmann J. Lexicon universale

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