Stratum
Goldenville strata in quarry in
Bedford,
Canada. These are
Middle Cambrian marine sediments. This formation covers over half of
Nova Scotia and is recorded as being 29,000 feet thick in some areas.
In geology and related fields, a stratum (plural: strata) is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers. The "stratum" is the fundamental unit in a stratigraphic column and forms the basis of the study of stratigraphy.
Characteristics
The
Permian through
Jurassic strata in the
Colorado Plateau area of southeastern
Utah demonstrates 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.
Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural processes. They may extend over hundreds of thousands of square kilometers of the Earth's surface. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs, road cuts, quarries, and river banks. Individual bands may vary in thickness from a few millimeters to a kilometer or more. Each band represents a specific mode of deposition: river silt, beach sand, coal swamp, sand dune, lava bed, etc.
Naming
Geologists study rock strata and categorize them by the material of beds. Each distinct layer is typically assigned to the name of sheet, usually based on a town, river, mountain, or region where the formation is exposed and available for study. For example, the Burgess Shale is a thick exposure of dark, occasionally fossiliferous, shale exposed high in the Canadian Rockies near Burgess Pass. Slight distinctions in material in a formation may be described as "members" (or sometimes "beds"). Formations are collected into "groups" while groups may be collected into "supergroups".
Gallery
| Strata on a mountain face in the French Alps |
| Outcrop of Upper Ordovician limestone and minor shale, central Tennessee; College of Wooster students. |
| Chalk Layers in Cyprus - showing classic layered structure. |
| Heavy minerals (dark) as thin strata in a quartz beach sand ( Chennai, India). |
|
See also
References
External links
 |
Look up stratum in Wiktionary, the free dictionary. |
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