Geoscience Reference
In-Depth Information
9.9 Conclusion
Fine-grained, wind-blown dust accumulated at intervals throughout the Quaternary
on the downwind margins of deserts in Africa, Australia, South America and Asia
(Pye,
1987
). In terms of their sorting and mineral composition, they are virtually
identical to the central European and North American loess mantles, which accumu-
lated downwind of the fluvioglacial outwash plains, so the term loess is used here
for any fine-grained eolian deposit, irrespective of its original provenance. The eolian
dust deposits in the Loess Plateau of central China are the thickest and most extensive
loess deposits in the world (Liu,
1985
;Liu,
1987
;Liu,
1991
; Kukla,
1987
). They
cover an area of 440,000 km
2
and attain thicknesses commonly in excess of 100 m
and more than 300 m near the city of Lanzhou. Detailed studies over the past three
decades have made the Chinese loess sequence with its alternation of unweathered
loess and intercalated soils one of the most informative continental sequences cov-
ering the last 2.5 Ma that exists on earth (Liu,
1991
). Comparison of the Chinese
loess record with evidence from deep sea cores and the Greenland and Antarctic ice
cores strongly confirms the climatic interpretation of the loess-soil couplets, with gla-
cial maxima synchronous with times of maximum dust deposition and interglacials
synchronous with times of maximum weathering and soil development. The loess
sequence in China illustrates how accurate dating and careful evaluation of different
lines of evidence is essential in reconstructing environmental change in deserts.
Finally, it is worth noting that although desert dust may prove a boon to those of
us seeking to reconstruct past climatic changes in deserts, it is a persistent bane to the
present-day inhabitants. I leave the last words to Kendrew (
1957
, p. 215): 'Dust, not
rain, is the great discomfort of life in arid lands. Except on still nights the air is full of
fine particles which percolate through the finest chinks into houses and even closed
boxes. Dust lies thick on every shelf, covers furniture, settles on food, and is inhaled
in the air we breathe'. John Steinbeck makes a very similar point in
TheGrapesof
Wrath
(1939), discussed in
Chapter 24
.
