Template:Short description Template:About
A loess (Template:IPAc-en, Template:IPAc-en; from Template:Langx {{#invoke:IPA|main}}) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust.<ref name="Frechen 2011"/> Ten percent of Earth's land area is covered by loesses or similar deposits.<ref name=" VasiljevicEtAl2011">Template:Cite journal</ref>
A loess is a periglacial or aeolian (windborne) sediment, defined as an accumulation of 20% or less of clay with a balance of roughly equal parts sand and silt (with a typical grain size from 20 to 50 micrometers),<ref>Template:Cite book</ref><ref>Template:Cite book</ref> often loosely cemented by calcium carbonate. Usually, they are homogeneous and highly porous and have vertical capillaries that permit the sediment to fracture and form vertical bluffs.
PropertiesEdit
Loesses are homogeneous, porous, friable, pale yellow or buff, slightly coherent, typically non-stratified, and often calcareous. Loess grains are angular, with little polishing or rounding, and composed of quartz, feldspar, mica, or other mineral crystals. Loesses have been described as rich, dust-like soil.<ref>Pearson Prentice Hall - World Studies - Europe and Russia</ref>
Loess deposits may become very thick: at more than a hundred meters in areas of Northwestern China and tens of meters in parts of the Midwestern United States. Loesses generally occur as blanket deposits that cover hundreds of square kilometers. The deposits are often tens of meters thick. Loesses often have steep or vertical faces.<ref>Neuendorf, K.E.K., J.P. Mehl Jr., and J.A. Jackson, 2005, Glossary of Geology. Springer-Verlag, New York City, 779 pp., Template:ISBN</ref> Because the grains are angular, loesses will often stand in banks for many years without slumping. This type of soil has "vertical cleavage", and thus, it can be easily excavated to form cave dwellings, which is a popular method of making human habitations in some parts of China. However, loesses can readily erode.
In several areas of the world, loess ridges have formed that had been aligned with the prevailing winds during the last glacial maximum. These are called "paha ridges" in America and "greda ridges" in Europe. The formation of these loess dunes has been explained as a combination of wind and tundra conditions.
EtymologyEdit
The word loess, with connotations of origin by wind-deposited accumulation, was introduced into English from the German {{#invoke:Lang|lang}} (1824),<ref>KARL CAESAR VON LEONHARD INTRODUCED THE TERM “LOESS”. INHIGEO, 2024.</ref> which can be traced back to Swiss German and is cognate with the English word loose and the German word {{#invoke:Lang|lang}}.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It was first applied to the Rhine River valley loesses around 1821.<ref>Template:Cite encyclopedia</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
History of researchEdit
The term "Löß" was first described in Central Europe by Karl Cäsar von Leonhard (1823–1824),<ref>Leonhard K. C. von (1823–1824). Charakteristik der Felsarten. 3 Vols., J. Engelmann Verlag Heidelberg, pp. 772.</ref> who had reported yellowish brown, silty deposits along the Rhine valley near Heidelberg.<ref name="Frechen 2011"/> Charles Lyell (1834) brought the term into widespread usage, observing similarities between "loess" and its derivatives along the loess bluffs in the Rhine and in Mississippi.<ref name="Frechen 2011" /> At the time, it was thought that the yellowish brown silt-rich sediment was of fluvial origin and had been deposited by large rivers.<ref name="Frechen 2011" /> The aeolian origin of the loesses was recognized later (Virlet D'Aoust 1857),<ref>Virlet D'Aoust P.T. (1857). "Observations sur un terrain d`origine météorique ou de transport aerien qui existe au Mexique et sur le phénomène des trombes de poussière auquel il doit principalement son origine". Geol. Soc. France, Full., 2d, Ser. 2, 129–139.</ref> particularly due to the convincing observations of loesses in China by Ferdinand von Richthofen (1878).<ref name="Frechen 2011"/><ref>Richthofen F. von (1878). "Bemerkungen zur Lößbildung". Verh Geol Reichsanst, Berlin, pp 1–13.</ref> A tremendous number of papers have been published since then, focusing on the formation of loesses and on loess/paleosol (older soil buried under deposits) sequences as the archives of climate and environment change.<ref name="Frechen 2011"/> These water conservation works have been carried out extensively in China, and the research of loesses in China has been ongoing since 1954. [33]
Much effort was put into setting up regional and local loess stratigraphies and their correlations (Kukla 1970, 1975, 1977).<ref>Kukla G. (1970). "Correlation between loesses and deep-sea sediments". Geologiske Foreningen Foerhandlingar 92: 148–180. Stockholm.</ref><ref>Kukla G. J. (1975). "Loess stratigraphy of Central Europe". In: Butzer K. W. & Isaac G. L. (eds.) After the Australopithecus, pp. 99–188. Mouton, The Hague.</ref><ref>Template:Cite journal</ref> However, even the chronostratigraphical position of the last interglacial soil correlating with marine isotope substage 5e was a matter of debate, due to the lack of robust and reliable numerical dating, as summarized, for example, by Zöller et al. (1994)<ref>Template:Cite journal</ref> and Frechen et al. (1997)<ref>Template:Cite journal</ref> for the Austrian and Hungarian loess stratigraphy, respectively.<ref name="Frechen 2011"/>
Since the 1980s, thermoluminescence (TL), optically stimulated luminescence (OSL), and infrared stimulated luminescence (IRSL) dating have been available, providing the possibility for dating the time of loess (dust) depositions, i.e., the time elapsed since the last exposure of the mineral grains to daylight.<ref name="Frechen 2011" /> During the past decade, luminescence dating has significantly improved by new methodological improvements, especially the development of single aliquot regenerative (SAR) protocols (Murray & Wintle 2000)<ref>Template:Cite journal</ref> resulting in reliable ages (or age estimates) with an accuracy of up to 5 and 10% for the last glacial record.<ref name="Frechen 2011"/> More recently, luminescence dating has also become a robust dating technique for penultimate and antepenultimate glacial loess (e.g. Thiel et al. 2011,<ref>Template:Cite journal</ref> Schmidt et al. 2011)<ref>Template:Cite journal</ref> allowing for a reliable correlation of loess/palaeosol sequences for at least the last two interglacial/glacial cycles throughout Europe and the Northern Hemisphere (Frechen 2011).<ref name="Frechen 2011"/><ref>Template:Cite journal</ref> Furthermore, the numerical dating provides the basis for quantitative loess research applying more sophisticated methods to determine and understand high-resolution proxy data including the palaeodust content of the atmosphere, variations of the atmospheric circulation patterns and wind systems, palaeoprecipitation, and palaeotemperature.<ref name="Frechen 2011" />
Besides luminescence dating methods, the use of radiocarbon dating in loess has increased during the past decades. Advances in methods of analyses, instrumentation, and refinements to the radiocarbon calibration curve have made it possible to obtain reliable ages from loess deposits for the last 40–45 ka. However, the use of this method relies on finding suitable in situ organic material in deposits such as charcoal, seeds, earthworm granules, or snail shells.<ref name=":0" /><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
FormationEdit
According to Pye (1995),<ref>Template:Cite journal</ref> four fundamental requirements are necessary for the formation of loess: a dust source, adequate wind energy to transport the dust, a suitable accumulation area, and a sufficient amount of time.<ref name="Frechen 2011"/>
Periglacial loessEdit
Periglacial (glacial) loess is derived from the floodplains of glacial braided rivers that carried large volumes of glacial meltwater and sediments from the annual melting of continental ice sheets and mountain ice caps during the spring and summer. During the autumn and winter, when the melting of the ice sheets and ice caps ceased, the flow of meltwater down these rivers either ceased or was greatly reduced. As a consequence, large parts of the formerly submerged and unvegetated floodplains of these braided rivers dried out and were exposed to the wind. Because the floodplains consist of sediment containing a high content of glacially ground flour-like silt and clay, they were highly susceptible to winnowing of their silts and clays by the wind. Once entrained by the wind, particles were then deposited downwind. The loess deposits found along both sides of the Mississippi River alluvial valley are a classic example of periglacial loess.<ref name="MuhsOthers2003a">Template:Cite journal</ref><ref name="esp.cr.usgs.gov">Template:Cite journal</ref>
During the Quaternary, loess and loess-like sediments were formed in periglacial environments on mid-continental shield areas in Europe and Siberia as well as on the margins of high mountain ranges like in Tajikistan and on semi-arid margins of some lowland deserts as in China.<ref name="Frechen 2011"/>
In England, periglacial loess is also known as brickearth.
Non-glacialEdit
Non-glacial loess can originate from deserts, dune fields, playa lakes, and volcanic ash.
Some types of nonglacial loess are:<ref>Template:Cite journal</ref>
- Desert loess produced by aeolian attrition of quartz grains;<ref>Whalley, W.B., Marshall, J.R., Smith, B.J. 1982, Origin of desert loess from some experimental observations, Nature, 300, 433-435.</ref>
- Volcanic loess in Ecuador and Argentina;
- Tropical loess in Argentina, Brazil and Uruguay;
- Gypsum loess in Spain;
- Trade wind loess in Venezuela and Brazil;
- Anticyclonic loess in Argentina.
The thick Chinese loess deposits are non-glacial loess having been blown in from deserts in northern China.<ref>Template:Cite journal</ref> The loess covering the Great Plains of Nebraska, Kansas, and Colorado is considered to be non-glacial desert loess.<ref name="MuhsOthers2003a"/> Non-glacial desert loess is also found in Australia<ref>Template:Cite journal</ref> and Africa.<ref name="esp.cr.usgs.gov"/>
FertilityEdit
Loess tends to develop into very rich soils. Under appropriate climatic conditions, it is some of the most agriculturally productive terrain in the world.<ref>Template:Cite book</ref>
Soils underlain by loess tend to be excessively drained. The fine grains weather rapidly due to their large surface area, making soils derived from loess rich. The fertility of loess soils is due largely to a high cation exchange capacity (the ability of the soil to retain nutrients) and porosity (the air-filled space in the soil). The fertility of loess is not due to organic matter content, which tends to be rather low, unlike tropical soils which derive their fertility almost wholly from organic matter.
Even well managed loess farmland can experience dramatic erosion of well over 2.5 kg/m2 per year. In China, the loess deposits which give the Yellow River its color have been farmed and have produced phenomenal yields for over one thousand years. Winds pick up loess particles contributing to the Asian Dust pollution problem. The largest deposit of loess in the United States which is the Loess Hills along the border of Iowa and Nebraska, has survived intensive farming and poor farming practices. For almost 150 years, this loess deposit was farmed with mouldboard ploughs and tilled in the fall, both intensely erosive practices. At times it suffered erosion rates of over 10 kilograms per square meter per year. Today this loess deposit is worked as low till or no till in all areas and is aggressively terraced.Template:Citation needed
Large areas of loess deposits and soilsEdit
Central AsiaEdit
An area of multiple loess deposits spans from southern Tajikistan up to Almaty, Kazakhstan.<ref>Template:Cite journal, Fig. 1 (b) showing the distribution of loess, deserts, and mountains in Central Asia (adopted from [T.S. Liu, Loess and the Environment, China Ocean Press, Beijing, 1985.]). The locality of the Chashmanigar loess section is indicated by the solid arrow.</ref>
East AsiaEdit
ChinaEdit
The Loess Plateau (Template:Zh), also known as the Huangtu Plateau, is a plateau that covers an area of some 640,000 km2 around the upper and middle reaches of China's Yellow River. The Yellow River was so named because the loess forming its banks gave a yellowish tint to the water.<ref>Template:Cite encyclopedia</ref> The soil of this region has been called the "most highly erodible soil on earth".<ref>John M. Laflen, Soil Erosion and Dryland Farming, 2000, CRC Press, 736 pages Template:ISBN</ref> The Loess Plateau and its dusty soil cover almost all of Shanxi, Shaanxi, and Gansu provinces; the Ningxia Hui Autonomous Region, and parts of others.Template:Citation needed
EuropeEdit
Loess deposits of varying thickness (decimeter to several tens of meters) are widely distributed over the European continent.<ref name=":0">Template:Cite journal</ref> The northern European loess belt stretches from southern England and northern France to Germany, Poland and the southern Ukraine and deposits are characterized by strong influences of periglacial conditions.<ref>Template:Cite journal</ref> South-eastern European loess is mainly deposited in plateau-like situations in the Danube basins, likely derived from the Danube River system.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> In south-western Europe, relocated loess derivatives are mostly restricted to the Ebro Valley and central Spain.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
North AmericaEdit
United StatesEdit
Template:More citations needed section The Loess Hills of Iowa owe their fertility to the prairie topsoils built by 10,000 years of post-glacial accumulation of organic-rich humus as a consequence of a persistent grassland biome. When the valuable A-horizon topsoil is eroded or degraded, the underlying loess soil is infertile and requires the addition of fertilizer to support agriculture.
The loess along the Mississippi River near Vicksburg, Mississippi, consists of three layers. The Peoria Loess, Sicily Island Loess, and Crowley's Ridge Loess accumulated at different periods during the Pleistocene. Ancient soils, called paleosols, have developed on the top of the Sicily Island Loess and Crowley's Ridge Loess. The lowermost loess, the Crowley's Ridge Loess, accumulated during the late Illinoian Stage. The middle loess, Sicily Island Loess, accumulated during the early Wisconsin Stage. The uppermost loess, the Peoria Loess, in which the modern soil has developed, accumulated during the late Wisconsin Stage. Animal remains include terrestrial gastropods and mastodons.<ref name="MillerOthers1">Miller, B.J., G.C. Lewis, J.J. Alford, and W.J. Day, 1985, Loesses in Louisiana and at Vicksburg, Mississippi. Guidebook, Friends of the Pleistocene Field Trip, 12-14 April, 1985. LA Agricultural Experimental Station, Louisiana State University, Baton Rouge, Louisiana. 126 pp.</ref>
OceaniaEdit
New ZealandEdit
Extensive areas of loess occur in New Zealand including the Canterbury Plains<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and on the Banks Peninsula.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Smalley, I.J., Davin, J.E. 1980. The First Hundred Years-A Historical Bibliography of New Zealand Loess. New Zealand Soil Bureau Bibliographic Report 28, 166pp.</ref> The basis of loess stratigraphy was introduced by John Hardcastle in 1890.<ref>*Hardcastle, J. 1890. On the Timaru loess as a climate register. Transcations & Proceedings of the New Zealand Institute 23, 324-332 (on line: Royal Society of New Zealand http://rsnz.natlib.govt.nz; reproduced in Loess Letter supplement 23, November 1988).</ref>Template:Primary source inline
South AmericaEdit
ArgentinaEdit
Much of Argentina is covered by loess. Two areas of loess are usually distinguished in Argentina: the neotropical loess north of latitude 30° S and the pampean loess.<ref name=Sagayo/>
The neotropical loess is made of silt or silty clay. Relative to the pampean loess the neotropical loess is poor in quartz and calcium carbonate. The source region for this loess is thought by some scientists to be areas of fluvio-glacial deposits the Andean foothills formed by the Patagonian Ice Sheet. Other researchers stress the importance of volcanic material in the neotropical loess.<ref name=Sagayo/>
The pampean loess is sandy or made of silty sand.<ref name=Sagayo>Template:Cite journal</ref>
See alsoEdit
- Template:Annotated link – North German loess regions
- Template:Annotated link – South German loess regions
- Template:Annotated link
ReferencesEdit
- Attribution
This article incorporates CC-BY-3.0 text from the reference "Loess in Europe: Guest Editorial".<ref name="Frechen 2011">Template:Cite journal</ref>
Further readingEdit
- Smalley, I. J. (editor) 1975. Loess Lithology & Genesis. Benchmark Geology 26. Dowden, Hutchinson & Ross 454pp.
- Smalley, I. J. 1980. Loess: A Partial Bibliography. Geobooks/Elsevier. Template:ISBN. 103pp.
- Rozycki, S. Z. 1991. Loess and Loess-like Deposits. Ossolineum Wroclaw Template:ISBN. 187pp.
External linksEdit
Template:Sister project Template:Sister project Template:Americana Poster
- 2006, The Secret of China's Vast Loess Plateau Suburban Emergency Management Project, Chicago, Illinois.
- 2007, New European Loess Map. Helmholtz Centre for Environmental Research, Leipzig, Germany.
- Glacial Deposits: Loess and Till. Illinois State Museum, Springfield, Illinois.
- Briedis. C.A., 2006, Loess Thickness Map (of Illinois). Illinois State Geological Survey, Champaign, Illinois.
- Heinrich, P.V., 2008, Loess map of Louisiana., Public Information Series. no. 12, Louisiana Geological Survey, Baton Rouge, Louisiana.
- Prior, J.C., and D.J. Quade, nd, The Loess Hills: A Geologic View. Iowa Geological Survey, Department of Natural Resources, Iowa City, Iowa.
- U.S. Geological Survey, 1999, Geology of the Loess Hills, Iowa
- U.S. Geological Survey, 2006, Eolian History of North America Why is loess important to study?
- The Loess Hills of Western Iowa
- The Loess Hills of Roztocze in Poland Template:Webarchive
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