Loess is a widespread, wind-transported, silt-dominated geologic deposit that covers about 10 percent of the Earth's land surface. Millions of people live in homes, work at businesses and use roads, railroads, and airports built on loess. Loess is also the parent material of the world's most productive agricultural soils. Because loess is deposited from the atmosphere it provides an important geologic archive of past atmospheric circulation that can be used to test atmospheric circulation models (Mahowald et al. 2006). Airborne dust, of which silt-size particles are an important component, also affects climate through its role in radiative transfer processes and by transporting mineral nutrients to the oceans, which affects primary productivity and the carbon cycle (Ridgwell 2002, Jickells et al. 2005). Loess deposits form where dust accumulates fast enough to form a distinctive silt-rich layer that buries soils or other geologic materials. A variety of geologic, climatic and biotic factors interact to form silt-size particles, mobilize and transport the silt from a source, and allow it to accumulate on the landscape.
Bettis, E.A. (2012): Climatic and biotic controls on silt production and accumulation of loess. Nature Education Knowledge.