Facies - Definition and Overview

The term facies refers to all of the characteristics of a particular geologic unit or one of its components, including the petrographic, lithographic, and paleontological aspects. For example, you might refer to a "tan, cross-bedded oolitic limestone facies" or a "blueschist facies". The characteristics of the rock unit come from the depositional environment.

Every depositional environment puts its own distinctive imprint on the sediment, making a particular facies. Thus, a facies is a distinct kind of rock for that area or environment. Each depositional environment grades laterally into other environments. This is referred to as a facies change when dealing with the rock record.

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.

See also

• Metamorphic Rock
• Stratum

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