Loess
A loess (US: /ˈlɛs, ˈlʌs, ˈloʊ.əs/, UK: /ˈloʊ.əs, ˈlɜːs/; from German: Löss [lœs]) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust.
[2] 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),[3][4] often loosely cemented by calcium carbonate.
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.
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.
[9][10] The term "Löß" was first described in Central Europe by Karl Cäsar von Leonhard (1823–1824),[11] who had reported yellowish brown, silty deposits along the Rhine valley near Heidelberg.
[1][13] 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.
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.
As a consequence, large parts of the formerly submerged and unvegetated floodplains of these braided rivers dried out and were exposed to the wind.
The fine grains weather rapidly due to their large surface area, making soils derived from loess rich.
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.
[36] 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.
[citation needed] Loess deposits of varying thickness (decimeter to several tens of meters) are widely distributed over the European continent.
[41][42] 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 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.
