Geoscience Reference
In-Depth Information
Salt
accumulation
Low precipitation
Animal pressures
on limited water
resources
Limited vegetation
Susceptible
shale etc.
Overgrazing
Rock
breakdown
Sediment removal
Deflation
Dolerite
intrusions
Sand
movement
Tectonic
disturbance
Lack of fluvial
intergration
Climatic
deterioration
Pan
Low slopes
Lack of fluvial
infilling
Figure 15.3
Flow diagram showing complex linkages of factors favouring pan and playa initiation and development by erosion
(in this case, predominantly by deflation) (after Goudie and Thomas, 1985).
attributed to the impact of meteors or volcanic crater de-
velopment (Wellington, 1955; Mabbutt, 1977; Goudie and
Thomas, 1985).
Faulting and downwarping have led to the develop-
ment of major regional basins of interior drainage in
some arid environments. For example, Cainozoic tectonic
activity, including block faulting, has been responsible
for the concentration of the intermontane basins in the
'Great Basin' and the 'Basin and Range' desert regions of
the southwestern United States (Smith and Street-Perrott,
1983, and see Chapter 4). Gentler Cainozoic tectonism has
contributed to the development of the Etosha and Mak-
gadikgadi basins in southern Africa (Wellington, 1955;
Thomas and Shaw, 1988) and the Eyre Basin in Australia
(Johns, 1989). Many of these large basins have responded
to major local and regional hydrological inputs by devel-
oping massive lakes responding to Quaternary climatic
fluctuations. These changes in hydrologic status are pre-
served in the sedimentary record or in former shorelines
(strandlines), and have been termed playa-lake complexes
by some authors (e.g. Eugster and Hardie, 1978; Eug-
their closed status and overflowed at times, as in the Bon-
neville and Lahontan Lakes of the Great Basin (Benson
et al.
, 1990).
On a smaller scale, lineaments, by acting as conduits
for groundwater movement, are the preferential sites for
the development of smaller pans, as suggested for some
of the features of the Texas High Plain (Osterkamp and
Wood, 1987) and the south and southeast Kalahari (Arad,
1984; Shaw and De Vries, 1988). Intruded bodies at depth
found in association with lineaments may also influence
pan location, as indicated by the geophysical studies of
Lokgware and Mogatse pans in the Kalahari (Farr
et al.
,
1982) and the influence of dolerite sills on the pans of the
Lake Chrissie complex in the eastern Transvaal (Welling-
ton, 1955). Ponding may also occur in the linear depres-
sions (
straats
) between longitudinal dunes, as in parts of
the Kalahari (Mallick, Habgood and Skinner, 1981), be-
tween strandlines of palaeolakes, as in the Dautsa Ridge
sequence of Lake Ngami (Shaw, 1985), or, by obstruction
of ephemeral channels, the extension of dunes as cited
with reference to western Australia (Gregory, 1914) and
