Facies

In geology, a facies (/ˈfeɪʃɪ.iːz/ FAY-shih-eez, US also /ˈfeɪʃiːz/ FAY-sheez; same pronunciation and spelling in the plural)[a] is a body of rock with distinctive characteristics.

[2] 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,[3] which replaced the earlier notions of Neptunism.

[5] A classic example of this law is the vertical stratigraphic succession that typifies marine transgressions and regressions.

Ideally, a sedimentary facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment.

Generally, geologists distinguish facies by the aspect of the rock or sediment being studied.

Eolianite carbonate facies (Holocene) on Long Island, Bahamas
Stratigraphic column on the north shore of Isfjord in Svalbard Norway . The vertical succession of rock types (representing sedimentary facies) reflects lateral changes in paleoenvironment.
Middle Triassic marginal marine siltstone and sandstone facies exposed in southern Utah