Слој (геологија)

Страта у Салти (Аргентина).

Голденвилски слојеви у каменолому у Бедфорду, Канада. Ово су морски седименти средњег камбријума. Ова формација покрива преко половине Нове Шкотске и забележена је као
8.800 m (29.000 ft) дебљине у неким областима.

Слој је геолошко тело, изграђено од мање или више истоветног материјала. То је основни елемент седиментих стена, настао као резултат једне континуиране фазе седиментације, чији је првобитни положај хоризонталан или субхоризонталан. Од подинског и повлатног слоја издвојен је површима слојевитости, које представљају границе механичког дисконтинуитета. Управно растојање између доње и горње површи слојевитости је дебљина слоја. Према дебљини, слојеви се деле на: лиске (испод 5 mm), плоче (од 5 до 50 mm), слојеве (5 до 60 cm) и банке (дебљина већа од 60 cm).

Слој је у простору одређен својим елементима пада, азимутом и падним углом. Врло је важно познавати елементе пада слоја, због одређивања елемената набора које слојеви изграђују. Тако је, у теренима који имају сложен тектонски склоп, важно одредити да ли су слојеви у преврнутом или нормалном положају. То се најчешће ради на основу испитивања карактеристика примарних планара, при чему се најчешће користе следећи критеријуми: биостратиграфско простирање, градациона слојевитост, критеријум односа кливажа према слојевитости, испитивање седиментних структура, анализа набора нижег реда, итд.

Карактеристике

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. 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. 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.

Врсте стратума

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. 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 customnarily 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 units when it is distinctive, widespread, and useful for stratigraphic correlation. A band is a thin stratum that is distingushiable 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.

Галерија

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  Strata on a mountain face in the French Alps

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  Interstate road cut through limestone and shale strata in East Tennessee

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  Rock strata at Depot Beach, New South Wales

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  Rainbow Basin Syncline in the Barstow Formation near Barstow, California. Folded strata.

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  Outcrop of Upper Ordovician limestone and minor shale, central Tennessee.

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  Chalk Layers in Cyprus - showing classic layered structure.

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  Heavy minerals (dark) as thin strata in a quartz beach sand (Chennai, India).

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  Stratified Island near La Paz, Baja California Sur, Mexico.

Литература

• Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. Glossary of Geology (5th ed.). Alexandria, Virginia; American Geological Institute. p 61. ISBN 0-922152764
• 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.
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• Boggs, Jr., Sam (2006). Principles of Sedimentology and Stratigraphy (PDF) (4th изд.). Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-154728-3. 
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• Lumsden, D.N., 1971. Facies and bed thickness distributions of limestones. Journal of Sedimentary Research, 41(2), pp.593-598.
• Ingram, R.L., 1954. Terminology for the thickness of stratification and parting units in sedimentary rocks. Geological Society of America Bulletin, 65(9), pp. 937-938.
• Kelley, V.C., 1956. Thickness of strata. Journal of Sedimentary Research, 26(4), pp.289-300.
• Australian Standards, 1993. Geotechnical site investigations. AS1726 – 1993. Sydney, Australia: Standards Association of Australia, 40 pp.
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• Tucker, Maurice, E. 1982. The Field Description of Sedimentary Rocks. Geological Society of London Handbook, Open University Press, Milton Keynes, UK, and John Wiley & Sons, NY. Table 5.2, p. 48.
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• Pool, Christopher A. (2007). Olmec Archaeology and Early Mesoamerica. Cambridge: Cambridge University Press. ISBN 978-0-521-78882-3. 
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• Frank, Adams Dawson (1938). The Birth and Development of the Geological Sciences. Baltimore: The Williams & Wilkins Company. 
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• Mathur S.M. (2008). Elements of Geology. стр. 129—130. ISBN 978-8120335158. 
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• „Chapter 5. Lithostratigraphic Units”. International Commission on Stratigraphy. 2013—2014. Приступљено 4. 6. 2014. CS1 одржавање: Формат датума (веза)
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• Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.-X. (2013). „International Chronostratigraphic Chart 2013” (PDF). stratigraphy.org. ICS. Приступљено 15. 6. 2014. CS1 одржавање: Формат датума (веза)
• Harshbarger, J.W.; Repenning, C.A.; Irwin, J.H. (1957). „Stratigraphy of the uppermost Triassic and the Jurassic rocks of the Navajo country”. U.S. Geological Survey Professional Paper. 291. doi:10.3133/pp291. 
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Спољашње везе

• GeoWhen Database
• International Commission on Stratigraphy Stratigraphic Guide