Geological formation

The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817.

[3] The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions.

The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures, fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen.

[2] Geologic formations are typically named after a permanent natural or artificial feature of the geographic area in which they were first described.

Formations were at first described as the essential geologic time markers, based on their relative ages and the law of superposition.

The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries.

[11] "Formation" is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes.

A geologic cross section of the Grand Canyon . Black numbers correspond to groups of formations and white numbers correspond to formations (click on picture for more information)
The Permian through Jurassic strata of the Colorado Plateau area of southeastern Utah demonstrate the principles of stratigraphy . These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park . From top to bottom: Rounded tan domes of the Navajo Sandstone , layered red Kayenta Formation , cliff-forming, vertically jointed, red Wingate Sandstone , slope-forming, purplish Chinle Formation , layered, lighter-red Moenkopi Formation , and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area , Utah.
Uluru (Ayers Rock) in Australia is underlain by the Mutitjulu Arkose, a formation composed almost entirely of a single lithology (arkosic sandstone).
The Summerville Formation is composed of alternating thin beds of two lithologies, mudstone and sandstone, penetrated by veins of a third lithology, gypsum.