Loess Records - Mineral Dust: A Key Player in the Earth System - page 407

Fig. 16.2 Gallery of loess exposures from around the world, 2: ( a ) non-glacial Holocene and
Pleistocene loess at Bignell Hill, Nebraska, Great Plains of the USA (see Muhs et al. ( 2008 )
for detailed study); ( b ) Pleistocene loess and paleosols exposed in a roadcut in the Palouse loess
country of eastern Washington, USA; ( c ) Pleistocene loess exposed in the Pampas region, northern
Buenos Aires province, Argentina; ( d ) Pleistocene loess and modern soil exposed on the Banks
Peninsula, South Island, New Zealand

16.3 Mineralogy and Geochemistry of Loess

Loess typically has a mineralogy that reflects a mixture of sources, but most loess is
derived from upper crustal source rocks. Exceptions to this include loesses derived
from mafic volcanic rocks in Iceland, parts of New Zealand, and parts of South
America. Elsewhere, on most continents, loess deposits typically include quartz,
plagioclase, K-feldspar, mica, calcite (sometimes with dolomite), and phyllosilicate
clay minerals (smectite, chlorite, mica, and kaolinite). Heavy minerals are usually
present but commonly are found only in small amounts. Bulk geochemical studies
show that the dominant constituent in loess is SiO 2 , which ranges from

45
to 75 % but is typically 55-65 %, reflecting a dominance of quartz. Lower
concentrations of quartz, feldspars, and micas in glaciogenic loess from North