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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
123:, 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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60:, 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
255:"Soils as a Source of Raw Materials for Ancient Ceramic production in the Maya region of Mexico: Micromorphological insight"
180:, both marine and terrestrial, make for distinctive marker horizons. Some marker units are distinctive by virtue of their
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Westgate, J. A.; Gorton, M. P. (1981). "Correlation
Techniques in Tephra Studies". In Self, S.; Sparks, R. S. J. (eds.).
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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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301:(5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp.
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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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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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81:beds) and impact spherule beds, and specific mega
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371:. Geological Society of America. p. 174.
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345:"What Really Killed the Dinosaurs?"
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24:Tephra horizons in Iceland
392:USGS (February 1, 2010).
343:BBC (17 September 2014).
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365:Evans, Kevin R. (2008).
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32:(also referred to as
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400:on October 10, 2012
299:Glossary of Geology
186:Witwatersrand Basin
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224:Radiometric dating
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71:Volcanic ash
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350:17 December
190:ferruginous
144:archaeology
62:sedimentary
50:isochronous
42:marker beds
458:Categories
240:References
121:Palynology
107:oil shales
103:cyclothems
83:turbidites
265:: 21â48.
193:quartzite
132:volcanoes
125:conodonts
79:bentonite
75:tonsteins
218:See also
182:magnetic
97:, black
67:sediment
38:key beds
176:Fossil
163:Iridium
111:iridium
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171:Danian
140:tephra
105:, and
99:shales
89:beds,
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429:ISBN
406:2019
373:ISBN
352:2019
324:ISBN
303:ISBN
285:link
212:grog
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