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]
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 8,800 m (29,000 ft) thick in some areas.
Typically, a stratum is generally one of a number of parallel layers that lie one upon another to form enormous thicknesses of strata.[1] The bedding surfaces (bedding planes) that separate strata represent episodic breaks in deposition associated either with periodic erosion, cessation of deposition, or some combination of the two.[3][4] Stacked together with other strata, individual stratum can form composite stratigraphic units that can extend over hundreds of thousands of square kilometers of the Earth's surface. Individual stratum can cover similarly large areas. 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 several meters or more. A band may represent a specific mode of deposition: river silt, beach sand, coal swamp, 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]
^ abcdeSalvador, A. ed., 1994. International stratigraphic guide: a guide to stratigraphic classification, terminology, and procedure. 2nd ed. Boulder, Colorado, The Geological Society of America, Inc., 215 pp. ISBN978-0-8137-5216-7.
^Neuendorf, K.K.E., Mehl, Jr., J.P., and Jackson, J.A. , eds., 2005. Glossary of Geology 5th ed. Alexandria, Virginia, American Geological Institute. 779 pp. ISBN0-922152-76-4.
^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.
^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.
^ abMurphy, 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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May 21, 2023
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For other uses see Stratum disambiguation and Strata disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Stratum news newspapers books scholar JSTOR May 2018 Learn how and when to remove this template message 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 Strata in Salta Argentina 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 8 800 m 29 000 ft thick in some areas Contents 1 Characteristics 2 Types of stratum 3 Gallery 4 See also 5 References 6 External linksCharacteristics Edit 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 thicknesses of strata 1 The bedding surfaces bedding planes that separate strata represent episodic breaks in deposition associated either with periodic erosion cessation of deposition or some combination of the two 3 4 Stacked together with other strata individual stratum can form composite stratigraphic units that can extend over hundreds of thousands of square kilometers of the Earth s surface Individual stratum can cover similarly large areas 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 several meters or more A band may represent a specific mode of deposition river silt beach sand coal swamp sand dune lava bed etc Types of stratum EditIn 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 Edit Strata on a mountain face in the French Alps Interstate road cut through limestone and shale strata in East Tennessee Rock strata at Depot Beach New South Wales Rainbow Basin Syncline in the Barstow Formation near Barstow California Folded strata Outcrop of Upper Ordovician limestone and minor shale central Tennessee Chalk Layers in Cyprus showing classic layered structure Heavy minerals dark as thin strata in a quartz beach sand Chennai India Stratified Island near La Paz Baja California Sur MexicoSee also EditArchaeological horizon Bed geology Geological formation List of rock formations Geologic map Geologic unit Lamination geology Law of superpositionReferences Edit a b c d e Salvador A ed 1994 International stratigraphic guide a guide to stratigraphic classification terminology and procedure 2nd ed Boulder Colorado The Geological Society of America Inc 215 pp ISBN 978 0 8137 5216 7 Neuendorf K K E Mehl Jr J P and Jackson J A eds 2005 Glossary of Geology 5th ed Alexandria Virginia American Geological Institute 779 pp ISBN 0 922152 76 4 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 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 a b Murphy MA and Salvador A 1999 International stratigraphic guide an abridged version Episodes 22 4 pp 255 272 External links Edit Look up stratum in Wiktionary the free dictionary GeoWhen Database Retrieved from https en wikipedia org w index php title Stratum amp oldid 1154544520, wikipedia, wiki, book, books, library,
