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The Origin and Geomorphological Significance of Closed Depressions in the Lubombo Mountains of Swaziland

1986; Wiley; Volume: 152; Issue: 1 Linguagem: Inglês

10.2307/632939

1475-4959

Andrew Watson,

Geochemistry and Geologic Mapping

In the Lubombo Mountains of Swaziland, south-east Africa, 53 closed depressions, from 50 m to 400 m in diameter and up to 5 m deep, have been identified. Frequently occurring in pairs or groups, the density of the pans reaches 0.3/km2. All of the depressions are located on remnants of the tilted African Plantation Surface. This is preserved in the region because the Jurassic rhyolites are less susceptible to weathering than are the surrounding basaltic and sedimentary rocks, which have been eroding since the Miocene. The closed depressions develop on the tuffaceous horizons within the acid volcanic sequence. They are probably the result of the local surface lowering, resulting from dissolution of plagioclase weathering products and possibly silica, in which case they are karstic. Though the presence of thick ferricretes suggests that the pans are of considerable age, possibly more than one million years old, there is no evidence of aeolian modification during the late Pleistocene arid phase.