Definition - What does Formation mean?
A Formation is a set or deposit of rocks with distinctive features of homogenous lithology which are or were once horizontally continuous. The rocks are composed substantially of the same kind of rock and are large enough so that they can be mapped. Each formation is given a name based on studies and understanding. Formation is also used as a basic unit of naming rocks in stratigraphic nomenclature.
Petropedia explains Formation
In terms of geology, a surface land form which is a part of homogenous lithology forms a formation. Formations are used to describe the odd shapes that rocks acquire through depositional processes. Formations should be delineated at the scale of geologic mapping that is practiced in that particular region. A formation thickness may range from less than a meter to several thousand meters. Formations are usually named for geographic areas in which they were first described. Formations are drilled during the development of an oil or gas well and well tests are done to show the details of the rocks and their physical and chemical properties. Analyzing all these properties helps geologists and scientists extrapolate the potential of hydrocarbon presence.