Stratum 554469 226174020 2008-07-17T04:12:34Z Wilson44691 4349401 Reduced caption for better format. {{dablink|This article is about the geologic use of the term, for other uses see [[Stratum (disambiguation)]]}} {{dablink|For other uses, see [[strata (novel)]] and [[strata title]].}} [[Image:IM000671.JPG|thumb|Goldenville strata in a quarry in [[Bedford, Nova Scotia|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 [[rock (geology)|rock]] or [[soil]] with 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 [[1 E11 m²|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 [[cliff]]s, [[road]] cuts, [[quarry|quarries]], and [[river]] banks. Individual bands may vary in thickness from a few [[millimeter]]s to a [[kilometer]] or more. Each band represents a specific mode of [[deposition]] -- river [[silt]], beach [[sand]], coal [[swamp]], [[sand dune]], [[lava]] bed, etc. [[Geologist]]s study rock strata and categorize them by the material in the beds. Each distinct layer is usually assigned to a "[[geologic formation|formation]]" name 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 [[fossil]]iferous, [[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." Groups may be collected into "supergroups." The stratum is the fundamental unit in a [[stratigraphic column]] and forms the basis of the study of [[stratigraphy]]. <gallery widths="180px" perrow=3> Image:Strata-french-alps.jpg|Strata on a mountain face in the French Alps Image:Rockstrata3435.JPG|Interstate road cut through [[limestone]] and [[shale]] strata in East [[Tennessee]] Image:Rock_Strata.jpg|Rock strata at [[Depot Beach]], [[New South Wales]] Image:Rainbow_Basin.JPG|Rainbow Basin Syncline near [[Barstow, California]]. Folded strata. Image:OrdOutcropTN.JPG|Outcrop of Upper Ordovician limestone and minor shale, central Tennessee; [[College of Wooster]] students. Image:Geology_of_Cyprus-Chalk.jpg|Chalk Layers in Cyprus - showing classic layered structure. Image:HeavyMineralsBeachSand.jpg|Heavy minerals (dark) as thin strata in a quartz beach sand ([[Chennai]], India). </gallery> ==See also== *[[Stratification]] *[[Polystrate fossil]] *[[List of publications in geology#Stratigraphy|Important publications in stratigraphy]] *[[Archaeology]] *[[Geologic map]] *[[Geologic unit]] *[[Geologic formation]] *[[Archaeological horizon]] ==External links== *[http://www.stratigraphy.org/geowhen/ GeoWhen Database] [[Category:Stratigraphy]] [[Category:Methods and principles in archaeology]] [[ca:Estrat]] [[de:Bank (Geologie)]] [[es:Estrato]] [[eu:Estratu]] [[fa:چینه]] [[fr:Strate (géologie)]] [[gl:Estrato]] [[ko:지층]] [[he:שכבה (גאולוגיה)]] [[it:Giacimento]] [[nl:Laag (stratigrafie)]] [[ja:地層]] [[pl:Warstwa (geologia)]] [[pt:Estrato geológico]] [[ru:Пласт (геология)]] [[sk:Vrstva (geológia)]] [[vi:Địa tầng]] [[uk:Надра]]