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Figure 11.4. Pleistocene lake marls near Bir Sahara, Western Desert of Egypt.
from 500 to 30 ka, with most of the Bir Tarfawi ages clustered between 180 and
80 ka for what they termed the Grey Lake Phase. They obtained three uranium-series
ages for Acheulian sites of 448
±
±
>
350 ka (ca. 600 ka),
but they rejected all of the ages they obtained for their Acheulian lake sites as either
stratigraphically reversed and far too young or with error terms so large as to be
meaningless (op. cit., p. 559). However, one important archaeological conclusion did
emerge from their work: the inception of the Saharan Middle Palaeolithic is no older
than 230 ka (op. cit., p. 358), so the youngest of the Saharan Acheulian industries
must be older than 230 ka (see Chapter 17 ). The three phases of high lake level
documented by Bergner and Trauth ( 2004 ) for Lake Naivasha in the Kenya Rift all lie
within the interval 175-60 ka and also post-date Acheulian occupation in this region
(see Chapter 17 ).
A study of lakes can often help explain otherwise obscure changes in river beha-
viour. The White Nile, for example, was transporting large volumes of sand under
conditions of very high energy flow around 30 ka, but its flow had dwindled to a trickle
by 20 ka at the height of the Last Glacial Maximum (LGM) (Williams et al., 2010b ).
The LGM (here defined as the time of maximum global ice volume as deduced from
the marine oxygen isotope record, or 21
47 ka, 542
389 ka and
2 ka: Mix et al., 2001 ) was a time when
the Sahara was even drier than today and desert dunes reached as far south as latit-
ude 12
±
°
N (Grove, 1980 ; Mainguet et al., 1980 ; Talbot, 1980 ). However, and more
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