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Origins and environments of pediments

1981; Taylor & Francis; Volume: 28; Issue: 3-4 Linguagem: Inglês

10.1080/00167618108729179

0016-7614

C. R. Twidale,

Groundwater and Isotope Geochemistry

Abstract Abstract Three types of pediment have been recognised. The first are cut bedrock surfaces, veneered (and hence smoothed and protected) by coarse alluvial debris. Characteristically developed in the Brachina area of South Australia, they form in the piedmont zone in areas of mixed sedimentary outcrop and in areas where there are large variations in river and stream discharge, including occasional high floods. They are not restricted to any conventionally defined climatic region or regions, though their development is favoured by stream regimes characteristic of arid and semiarid lands. The second and third types are typical of granite regions. The debris veneer of the second form, well developed around Ucontitchie Hill, mainly consists of weathered rock in situ, though in places there is also a thin discontinuous veneer of transported material. The mantis consists of grus and is readily eroded, exposing the weathering front as a rock platform or pediment, such as that found adjacent to Corrobinnie Hill. The mantled and rock forms are well developed in arid and semiarid tropical and subtropical lands, though it is suggested that they have their congeners in cooler mid latitude areas. Brachina type pediments characteristically occur in flights, and they persist in the landscape, as also do rock pediments. But the Ucontitchie type is readily eroded and is a single cycle form. Brachina and Ucontitchie type pediments are the most common members of an isomorphous series. Similarly, the Ucontitchie and Corrobinnie types of granitic areas are end members of a continuum. None of three pediment forms indentified is necessarily associated with scarp retreat.