geologyand related fields, a stratum (plural: "strata") is a layer of rock or soilwith internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. 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, roadcuts, quarries, and riverbanks. Individual bands may vary in thickness from a few millimeters to a kilometeror more. Each band represents a specific mode of deposition-- river silt, beach sand, coal swamp, sand dune, lavabed, etc. Geologists study rock strata and categorize them by the material in the beds. Each distinct layer is usually assigned to a "formation" name usually based on a town, river, mountain, or region where the formation is exposed and available for study. For example, the Burgess Shaleis a thick exposure of dark, occasionally fossiliferous, shaleexposed high in the Canadian Rockiesnear Burgess Pass. Slight distinctions in material in a formation may be described as "members" or sometimes "beds." Formations are collected into "groups." Groups may be collected into "supergroups."
The stratum is the fundamental unit in a
stratigraphiccolumn and forms the basis of the study of stratigraphy. limestoneand shalestrata in East Tennessee Depot Beach, New South Wales Barstow, California. Folded strata.
College of Woosterstudents. Chennai, India).
*Important publications in stratigraphy
* [http://www.stratigraphy.org/geowhen/ GeoWhen Database]
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