Stratum
In
geology and related fields, a stratum is a layer of 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 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.
Encyclopedia
In
geology and related fields, a
stratum is a layer of 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 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.
Geologists study rock strata and categorize them by the material in the beds. Each distinct layer is usually assigned 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 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." 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.
See also
- Stratification
- Important publications in stratigraphy
- Archaeology
- Geologic map
- Geologic unit
- Geologic formation
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