6.3 SEDIMENTARY MODELS
207
Fig. 6.17. Map of the Pre-Cambrian Witwatersrand basin of South Africa, to show the location of gold- and
uranium-bearing alluvial fans. (Based on Pretorius, 1979, and Brock and Pretorius, 1964.)
6.3.2.3 Eolian Depositional Systems
6.3.2.3.1 Modern deserts and eolian environments
Significant volumes of eolian sediment are only deposited in deserts, though minor
quantities may develop along beaches and barrier islands. Deserts are regions characterized by aridity, and often by extremes of temperature (Williams and Bailing, 1996).
Modern deserts occur in the centers of continents away from marine influence, and along
the western seaboards of continents where prevailing winds blow offshore (Fig. 6.20).
Not all deserts are characterized by high temperatures. In some arid periglacial environments wind action forms ventifacts and dust clouds that may ultimately settle as loess
(see Section 4.3.2).
Eolian sands are only one of a wide range of deposits that occur in modern deserts
(Fig. 6.21). Many deserts are equilibrial environments which range from sand-blasted
rock pediments, via boulder or gravel strewn surfaces, to fiat sand sheets. Vast areas of
207
Fig. 6.17. Map of the Pre-Cambrian Witwatersrand basin of South Africa, to show the location of gold- and
uranium-bearing alluvial fans. (Based on Pretorius, 1979, and Brock and Pretorius, 1964.)
6.3.2.3 Eolian Depositional Systems
6.3.2.3.1 Modern deserts and eolian environments
Significant volumes of eolian sediment are only deposited in deserts, though minor
quantities may develop along beaches and barrier islands. Deserts are regions characterized by aridity, and often by extremes of temperature (Williams and Bailing, 1996).
Modern deserts occur in the centers of continents away from marine influence, and along
the western seaboards of continents where prevailing winds blow offshore (Fig. 6.20).
Not all deserts are characterized by high temperatures. In some arid periglacial environments wind action forms ventifacts and dust clouds that may ultimately settle as loess
(see Section 4.3.2).
Eolian sands are only one of a wide range of deposits that occur in modern deserts
(Fig. 6.21). Many deserts are equilibrial environments which range from sand-blasted
rock pediments, via boulder or gravel strewn surfaces, to fiat sand sheets. Vast areas of