Geological formation – a natural aggregation of rock masses connected by common genesis, i.e. emerging in similar physical, geographical and tectonic (geodynamical) environment. Formation is characterized by hundreds and even thousands meters of depth and areas of many thousands square kilometers.

Geological formations may be sedimentary, volcanic, volcanic-sedimentary, intrusive-magmatic, metamorphic, and ore formations. Formations differ by geological types and types of mineral resources – carbon-bearing, phosphates-bearing, salt-bearing, etc. Often logical combinations of formations are called associations.

Geological formation is characterized by certain combination of rock (principal and associated), by specifics of their alternation (e.g., cycling), by shape (extension, depth). Each geological formation is associated with certain geological environment, so geological data analysis (formation analysis) is widely used to simulate geological evolution of regions. It allows for defining the tectonic genesis and the development mode of a given region, the type of major tectonic framework it belonged to (geosynclines, orogenic belts, plates, oceans) and its evolution stage. Besides tectonic (geodynamic) environment, climatic conditions also had very big impact on the composition of sedimentary formations of continental and shallow-marine origin. Due to that sedimentary formations are classified not only by tectonic features, but also by types of climate.