In geology, a facies (pronounced variously as /ˈfʃz/, /ˈfsz/ or /ˈfæʃz/ ['faysheez', 'fayseez' or 'fash-eez']; plural also 'facies') is a body of rock with specified characteristics,[1] which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formation), and the changes that may occur in those attributes over a geographic area. It is the sum total characteristics of a rock including its chemical, physical, and biological features that distinguishes it from adjacent rock.[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.

The sequence of minerals that develop during progressive metamorphism (that is, metamorphism at progressively higher temperatures and/or pressures) define a facies series.

Seismic facies

Seismic facies are mappable three-dimensional seismic units composed of reflection units whose parameters differ from adjacent facies units.

See also