Silt-dominated sediment of eolian (windblown) origin. Loess is a common deposit in and near areas that were glaciated during the Quaternary Period, and most loess deposits are indirectly related to glaciation. Eolian landforms Quaternary Loess is a well-sorted clastic deposit which is unconsolidated, relatively homogeneous, seemingly nonstratified, and extremely porous. Colors range from buff to shades of pink, gray, yellow, or brown. Silt-sized particles, most of which are 0.0002–0.002 in. (0.005–0.05 mm) in diameter, usually make up 60–90% of the deposit, with small amounts of fine sand and small to moderate amounts of clay-sized material. The particles are generally angular to subangular. Quartz is the dominant mineral, with subordinate amounts of feldspar, calcite, dolomite, clay minerals, and small amounts of other minerals. Clay minerals are primarily smectite, illite, and chlorite. They occur as silt-sized aggregates and, along with calcite, as coatings or fillings on silt grains, in interstices, and in vertical tubes left from the decay of grass roots. These latter characteristics partially bind the particles together and give loess with relatively large dry strength. As a result, many loess deposits maintain near-vertical slopes in both natural and artificial cuts. Loess occurs as a relatively thin (generally <90 ft or 30 m), blanket-type deposit which drapes over an irregular landscape. It is common in many areas of the world, but is particularly thick near valleys that served as meltwater drainageways during Quaternary glaciation. Loess also may be derived from desert areas, in which case the particles must be produced by either weathering processes or eolian abrasion. Sedimentology Soil |
