OLDLANDS: CHARACTERISTICS AND IMPLICATIONS BASED ON THE AUSTRALIAN EXPERIENCE |
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| Authors: | C R Twidale |
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| Institution: | Department of Geology and Geophysics , University of Adelaide , Adelaide, South Australia 5005 Australia |
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| Abstract: | Oldlands are complex surfaces of low relief preserved on Precambrian shields and cratons and Paleozoic massifs. Interpretation of their character and age is difficult, but as a consequence of its particular location and of conceptual developments, much of the Australian Craton is now susceptible to analysis in terms of exhumation, etching, and multistage development. Exhumed surfaces of many ages are recorded. Long periods of weathering and erosion generated low relief, although recurrent block tectonics produced a differentiated topography and also resulted in regolithic veneers, some of them with mineral concentrations that later became duricrusts. The associated landforms are of various ages, but are mostly of Early and Middle Tertiary ages. Cretaceous and Early to Middle Tertiary etch forms are widely developed and preserved. Earlier Mesozoic (Jurassic, Triassic) surfaces are also represented or implied. Many cratonic landforms are related to the subsurface weathering and subsequent erosion to which oldlands have been subjected, to the exploitation of fractures in the basement rocks, to underprinting from fracture zones in the basement, and to deep erosion, causing rivers to breach alien structures. Multistage as well as two-stage forms are common, and pre-weathered detritus derived from regoliths was contributed to adjacent basins. Key words: oldland, etch surface, underprinting, duricrust, paleosurface.] |
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