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relatively thick deposits of mostly unaltered sediment with intercalated paleosols.
Paleosols represent periods of landscape stability when loess deposition ceased or
at least slowed significantly. Studies from several continents show that loess in
most regions was deposited during glacial periods and paleosols formed during
interglacial and interstadial periods.
Keywords
Loess Glacial Interglacial Silt Paleosol Deposition
Mineralogy Geomorphology Sediment Stratigraphy Geochronology
Dispersal Paleoclimate Records Archive Aeolian Quaternary
16.1
Introduction
Loess is aeolian (windblown) sediment and is one of the most extensive surficial
deposits on the surface of the Earth. Loess has come to be regarded as one of
the most important archives of long-term dust deposition and Quaternary climate
change. Combined with intercalated paleosols (buried soils), loess provides one
of the most complete terrestrial records of glacial-interglacial cycles. Loess is
distinctive in that it is one of the few Quaternary sediments that provides a direct
record of atmospheric circulation. Thus, given favorable circumstances, loess can
be used to reconstruct synoptic-scale paleoclimatology over millennial timescales.
Finally, loess is unusual in that it can be dated directly using methods, such
as luminescence geochronology, that require only the sediment itself. Thus, the
combination of loess deposits, fossil remains, and intercalated paleosols provides
a highly valued source of information of Quaternary paleoclimate.
16.2
Definition of Loess
Loess can be defined as sediment, dominated by silt-sized particles, that has been
entrained, transported, and deposited by the wind. It differs from other dust archives
(deep-sea cores, ice cores; see Muhs (
2013a
) for a review) in that it is found on
land and is identifiable in the field as a distinct sedimentary body (Figs.
16.1
and
16.2
). Loess occupies an intermediate position in a continuum of aeolian
sediments, with an average particle size that is smaller than windblown sand (2-
0.05 mm) but coarser than long-range-transported (LRT) dust (typically <10 m).
Commonly, loess contains 60-90 % silt-sized (50-2 m diameter) particles, with
smaller amounts of sand (>50 m)andclay(<2 m). Some loess deposits are
more sand rich and others are more clay rich, but all have a dominance of silt-
sized particles. Loess is also much more poorly sorted than aeolian sand or LRT
dust. The wide range of mean particle size and relatively poor sorting can be
the result of (a) multiple sources, (b) clay-sized particles being transported as
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