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Asia it is far older, with strong evidence of aridity in that region by around 24 Ma
(Dupont-Nivet et al.,
2007
; Dupont-Nivet et al.,
2008
; Sun et al.,
2010
). In central
Australia, the inception of aridity seems to be far younger, with major inland lakes
persisting until at least 1 million years ago before giving way to desert playa lakes and
dunes fashioned from wind-blown quartz and gypsum sand-sized particles (Chen,
1989
; Chen and Barton,
1991
; Fujioka and Chappell,
2010
). Further afield, in the
present Congo/Zaıre Basin of central Africa, there are much older deposits of red
desert sands that predate the oldest sands of the present Kalahari Desert. We therefore
need to allow for local differences in the timing of early desiccation that are linked
to regional climatic and tectonic factors and should not expect a similar sequence
of Cenozoic events in the deserts of China, India, Australia, southern Africa and the
Americas.
3.4 Quaternary climatic fluctuations in deserts
Before we conclude this brief survey of Cenozoic cooling and desiccation, it is
important to draw attention to a number of unique climatic changes that took place
at the onset of the Pleistocene. The start of the Pleistocene epoch (2.6 Ma to 12 ka)
was heralded by a number of important regional environmental changes, including a
major expansion of Northern Hemisphere ice, renewed widespread accumulation of
wind-blown dust in the Loess Plateau of central China and the onset of a cooler, drier
climate in the Ethiopian Highlands of East Africa. It is probably not a coincidence
that the first evidence of stone tool-making by ancestral humans in the Afar Desert
of Ethiopia is dated to around 2.5 Ma - a time of abrupt and rapid environmental
changes in that region (see
Chapter 17
). Closure of the Panama seaway at the end
of the Pliocene would have diverted warm ocean water northwards into the North
Atlantic, thereby providing a sufficient source of moist air from the ocean to feed the
growing ice caps in North America, Greenland and north-west Europe.
Subdividing the Pleistocene has often engendered more heat than light, but a
good case exists for using the Brunhes-Matuyama paleomagnetic boundary (dated to
0.78 Ma) to delineate the boundary between Lower and Middle Pleistocene (Pillans,
2003
). This proposal also accords with a similar and much earlier recommendation
in the volume edited by Butzer and Isaac (
1975
) that arose from a Burg Wartenstein
symposium dealing with cultural change in the Middle Pleistocene. The Upper Pleis-
tocene extends, somewhat arbitrarily, from the peak of the last interglacial to the start
of the Holocene (i.e., from 125 ka to 12 ka). The Upper Pleistocene thus consists of a
single interglacial-glacial cycle, culminating in the Last Glacial Maximum, dating to
21
2 ka ago (Mix et al.,
2001
), when global ice volume was last at its maximum and
sea levels were correspondingly low (
±
120 m: Yokoyama et al.,
2000
; Lambeck and
Chappell,
2001
). The most recent subdivision of the Quaternary is into four Stages
or Ages and simply adds an earlier phase for what was once the late Pliocene. These
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