Deserts of the World - Design with the Desert: Conservation and Sustainable Development - page 13

synclines and anticlines. The underthrusting of Iran by the Arabian plate resulted in the
complex folding of the Zagros Mountains. Eruptive rocks occur in zones of structural
weakness, in the highland zones of Turkey and Iran, and also adjacent to the major fault-
ing zones of the Dead Sea Lowlands and the Red Sea.
Such structural considerations thus underlie the gross morphology of the region. The
detailed morphology owes much to environmental changes of the Tertiary and Pleistocene.
Widespread humid conditions in the late Tertiary may have been of particular importance. 68
The evidence for this is provided by the development of erosional and weathering features
on basalt lava flows of known age. Intense lateritic weathering * is evident on a basalt flow
3.5 million year old, as is extensive fluvial dissection. By contrast, a younger flow, dated
to the early Pleistocene (c. 1.3 million year old), shows no such features. Blocked-up linear
drainage systems may date back to this stage, and associated gravel fans interfinger with
the deposits of the regressing late Pliocene/early Pleistocene sea.
During the Quaternary, long-continued humid periods appear to have been much less
significant, though the evidence for pluvials and interpluvials is well known. Indeed, it
was in the Dead Sea trough that some of the first evidence for pluvials was identified.69 69
Nonetheless, aridity has probably been a dominant feature for much of the Pleistocene
(Figure 1.12). 70 Unfortunately, precisely dated, reliable palaeoenvironmental information
is not readily available, especially before about 40,000 year BP, and attempts at correlation
across the very varied climatic environments of the Near East have so far produced results
that are confused both temporally and spatially. So, for example, an analysis of palynological
data for a range of sites, for the Pleniglacial (c. 50,000-14,000 year BP), found that not only
are there striking differences in vegetational and climatic history between the Levant and
western Iran, but that even within the Levant the climatic history deduced for northern
Israel cannot be brought into line with that of northwestern Syria. 71 For that reason, at
present, it is probably prudent to provide some results from relatively well-dated situations
from selected sites across the area, rather than to try to produce premature correlations.
FIGURE 1.12
Photograph of the Al Rub al' Kali in northern Yemen. (Courtesy of Robert H. Webb.)
* Lateritic weathering typically occurs in tropical climates and results in distinctive deposits bearing iron and
aluminum oxides. Pluvials are geologic periods of increased precipitation.