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rock that is readily recognized on the basis of either its distinct physical characteristics or fossil content and can be mapped over a very large geographic area. As a result, a key bed is useful for correlating sequences of sedimentary rocks over a large area. Typically, key beds were created as
134:, the study of fossil pollens and spores, routinely works out the stratigraphy of rocks by comparing pollen and spore assemblages with those of well-known layersâa tool frequently used by petroleum exploration companies in the search for new fields. The fossilised teeth or elements of
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in order to measure deposition and erosion rates in a marsh or pond environment. The materials used for such an artificial horizon are chosen for their visibility and stability and may be brick dust,
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are types of key beds created by instantaneous events. The widespread accumulation of distinctive sediments over a geologically short period of time have created key beds in the form of
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of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age (
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layers are associated with bolide impacts and are not unique, but when occurring in conjunction with the extinction of specialised tropical planktic
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71:, permit the mapping of land masses and bodies of water throughout the history of the earth. They usually consist of a relatively thin layer of
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the result of either instantaneous events or (geologically speaking) very short episodes of the widespread deposition of a specific types of
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H.V. Cabadas-BĂĄez, S. Sedov, S. JimĂ©nez-Ălvarez, D. Leonard, B. Lailson-Tinoco, R. GarcĂa-Moll, I. Ancona-AragĂłn, L. HernĂĄndez. (2018).
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create useful markers, as different volcanic eruptions and impacts produce beds with distinctive compositions. Marker horizons of
266:"Soils as a Source of Raw Materials for Ancient Ceramic production in the Maya region of Mexico: Micromorphological insight"
191:, both marine and terrestrial, make for distinctive marker horizons. Some marker units are distinctive by virtue of their
329:
Westgate, J. A.; Gorton, M. P. (1981). "Correlation
Techniques in Tephra Studies". In Self, S.; Sparks, R. S. J. (eds.).
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80:. As the result, key beds often can be used for both mapping and correlating sedimentary rocks and dating them.
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International
Stratigraphic Guide - Geological Society of America (1994) - Amos Salvador (editor)
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qualities. The Water Tower Slates, forming part of the
Hospital Hill Series in the
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species, signal a reliable marker horizon for the
CretaceousâPaleogene boundary.
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312:(5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp.
67:, and used in conjunction with fossil floral and faunal assemblages and
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Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005)
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One particular bolide impact 66 million years ago, which formed the
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On a much smaller time scale, marker horizons may be created by
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Stratigraphic units used to correlate the age of strata in rocks
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120:. A well-known example of a key bed is the global layer of
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quartzite and a speckled bed are used as marker horizons.
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that occurs in a thin, global layer of clay marking the
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which is particularly magnetic. From the same series a
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92:beds) and impact spherule beds, and specific mega
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382:. Geological Society of America. p. 174.
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294:: CS1 maint: multiple names: authors list (
379:The Sedimentary Record of Meteorite Impacts
225:, sand, kaolin, glitter or feldspar clay.
270:BoletĂn de la Sociedad GeolĂłgica Mexicana
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356:"What Really Killed the Dinosaurs?"
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436:Historical Geology of South Africa
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333:. Boston: Kluwer. pp. 73â94.
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189:faunal and floral assemblages
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153:are used as a dating tool in
126:CretaceousâPaleogene boundary
138:are an equally useful tool.
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35:Tephra horizons in Iceland
403:USGS (February 1, 2010).
354:BBC (17 September 2014).
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434:Truswell, J. F. (1970).
376:Evans, Kevin R. (2008).
282:10.18268/BSGM2018v70n1a2
438:. Cape Town: Purnell.
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43:(also referred to as
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411:on October 10, 2012
310:Glossary of Geology
197:Witwatersrand Basin
57:stratigraphic units
235:Radiometric dating
104:beds, shell beds,
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245:Stratigraphy
219:limnologists
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178:foraminifera
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106:marine bands
82:Volcanic ash
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361:17 December
201:ferruginous
155:archaeology
73:sedimentary
61:isochronous
53:marker beds
469:Categories
251:References
132:Palynology
118:oil shales
114:cyclothems
94:turbidites
276:: 21â48.
204:quartzite
143:volcanoes
136:conodonts
90:bentonite
86:tonsteins
229:See also
193:magnetic
108:, black
78:sediment
49:key beds
187:Fossil
174:Iridium
122:iridium
18:Key bed
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182:Danian
151:tephra
116:, and
110:shales
100:beds,
84:beds (
65:strata
55:) are
440:ISBN
417:2019
384:ISBN
363:2019
335:ISBN
314:ISBN
296:link
223:grog
217:and
145:and
102:coal
98:peat
88:and
278:doi
112:in
51:or
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