Stratum

Source: Wikipedia, the free encyclopedia.
For other uses, see Stratum (disambiguation) and Strata (disambiguation).
Salta (Argentina
)
Middle Cambrian marine sediments. This formation covers over half of Nova Scotia
and is recorded as being 8,800 m (29,000 ft) thick in some areas.

In geology and related fields, a stratum (pl.: strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as either bedding surfaces or bedding planes.[1] Prior to the publication of the International Stratigraphic Guide,[1] older publications have defined a stratum as either being either equivalent to a single bed or composed of a number of beds; as a layer greater than 1 cm in thickness and constituting a part of a bed; or a general term that includes both bed and lamina.[2] Related terms are substrate and substratum (pl.substrata), a stratum underlying another stratum.

Characteristics

The Permian through Jurassic strata in 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.

Typically, a stratum is generally one of a number of parallel layers that lie one upon another to form enormous

sand dune, lava
bed, etc.

Types of stratum

In the study of rock and sediment strata, geologists have recognized a number of different types of strata, including bed, flow, band, and key bed.[1][5] A bed is a single stratum that is lithologically distinguishable from other layers above and below it. In the classification hierarchy of sedimentary lithostratigraphic units, a bed is the smallest formal unit. However, only beds that are distinctive enough to be useful for stratigraphic correlation and geologic mapping are customarily given formal names and considered formal lithostratigraphic units. The volcanic equivalent of a bed, a flow, is a discrete extrusive volcanic stratum or body distinguishable by texture, composition, or other objective criteria. As in case of a bed, a flow should only be designated and named as a formal lithostratigraphic unit when it is distinctive, widespread, and useful for stratigraphic correlation. A band is a thin stratum that is distinguishable by a distinctive lithology or color and is useful in correlating strata. Finally, a key bed, also called a marker bed, is a well-defined, easily identifiable stratum or body of strata that has sufficiently distinctive characteristics, such as lithology or fossil content, to be recognized and correlated during geologic field or subsurface mapping.[1][5]

Gallery

See also

References

  1. ^
    ISBN 978-0-8137-5216-7
    .
  2. ISBN 0-922152-76-4
    .
  3. ^ Davies, N.S., and Shillito, A.P. 2021, True substrates: the exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces. Sedimentology. published online 22 May 2021, doi: 10.1111/sed.12900.
  4. ^ Davies, N.S., and Shillito, A.P. 2018, Incomplete but intricately detailed: the inevitable preservation of true substrates in a time-deficient stratigraphic record. Geology, 46, 679–682.
  5. ^ a b Murphy, MA., and Salvador, A., 1999. International stratigraphic guide—an abridged version. Episodes, 22(4), pp.255-272.

External links

Look up stratum in Wiktionary, the free dictionary.
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