Stratigraphic unit

A stratigraphic unit is a volume of rock of identifiable origin and relative age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it.

[1] A bed is a lithologically distinct layer within a member or formation and is the smallest recognisable stratigraphic unit.

[5] Formations are the primary units used in the subdivision of a sequence and may vary in scale from tens of centimetres to kilometres.

[4] A sequence of fossil-bearing sedimentary rocks can be subdivided on the basis of the occurrence of particular fossil taxa.

[6] The five commonly used types of biozone are assemblage, range, abundance, interval and lineage zones.

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.