formacj

Formacj, a term used in geology as a shorthand for formacja (formation), denotes a fundamental lithostratigraphic unit: a body of rock with recognizable characteristics that is large enough to be mapped at the Earth's surface or in the subsurface.

A formacja is defined by a distinctive lithology or a combination of lithologies (for example sandstone and shale), a recurring set of sedimentary structures, or fossil content that distinguishes it from neighboring strata. The boundaries at the top and bottom are placed where those characteristics change, which may coincide with unconformities or gradual transitions. The name is typically derived from a geographic locality near where the formation is well exposed.

Formacje are subdivided into members and beds; members are smaller units with consistent lithology, while beds are the smallest definable layers. They are used to describe and correlate rock sequences across regions, aiding the reconstruction of past depositional environments, paleogeography, and tectonic history.

They facilitate regional correlation and interpretation of geological history, and are important in resource exploration, groundwater studies, and environmental geology. In practice, the concept is widely used in geological surveys worldwide, though terminology can vary. In English-language geology, the standard term is "formation," while Polish usage often uses "formacja" and its abbreviated form "formacj." See also stratigraphy, lithostratigraphy, members and beds.