Aeolian landscapes and bedforms - Arid Zone Geomorphology - page 437

from samples collected from shallow pits in dunes, which
gave a relatively simple picture of sand sea history, dune
accumulation and inferred aridity (Stokes, Thomas and
Washington, 1997) (Figure 17.16).
As more age determinations have been achieved, pic-
tures that are complex to interpret emerge. These include
spatially variable accumulation histories along short dis-
tances of individual dunes (Telfer and Thomas, 2006), but
also that, as more ages are added to data sets and sam-
pling strategies become more intense, apparent discrete
phases of accumulation can disappear and also appar-
ent continuous deposition can be represented by full sets
of age determinations (Stone and Thomas, 2008) (Fig-
ure 17.16). While a number of factors could contribute
to such a situation (e.g. the error range on ages, possible
post-depositional sediment mixing, sampling issues, the
complex suite of factors that affect dune activity and sedi-
ment preservation), this demonstrates a number of impor-
tant factors in elucidating sand sea histories. First, simple
relationships between dunefield accumulation and broad
global climate trends senso Sarnthein (1978) have not oc-
curred. Second, variability in depositional ages can be
marked between dunes within an individual sand sea, be-
cause net accumulation and preservation does not appear
to occur simultaneously at all points within a dunefield.
Third, care needs to be exerted in terms of how chronolo-
gies are produced and how many ages are used to produce
conclusions for individual sand seas: the dunefield, not
the individual dune, is the natural unit from which to
gain an appropriate picture of a system history (Stone and
Thomas, 2008).
Luminescence dating is also shedding new light on
the records of past climate change preserved within loess
bodies. Independent direct dating of loess has challenged
previous chronologies based on magnetic susceptibly or
record correlation (e.g. Singhvi et al. , 2001; Stevens et al. ,
2007). Contrary to views that loess deposits provide a
spatially uniform record of deposition over large areas,
these studies show that accumulation histories can be
as complex and variable as those derived from within
sand seas.

and the processes responsible for sediment mobilisation,
transport and settlement. Gaining this knowledge requires
investigations as a range of spatial and temporal scales
(Thomas and Wiggs, 2008), and in this chapter we have
primarily considered what controls the nature and char-
acter of the landscape features of aeolian systems: sand
seas and loess deposits. These spatially extensive features
provide the context in which the operation of aeolian pro-
cesses and the generation of bedforms play out, and these
process- and landform-focused dimensions of aeolian sys-
tems are examined in detail in the next chapters.

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17.6 Conclusions

Aeolian deposits are a major - though not as extensive as
widely assumed - component of dryland environments.
Determining where they are, and why they are there, re-
quires the application of scientific approaches that eluci-
date the timing of deposition, the controls on deposition