PERENNIAL PROBLEMS IN THE STUDY OF LATERITE - A REVIEW

There are perennial problems in the investigation of laterite. (i) The development of an acceptable terminology to describe the forms and processes associated with laterite genesis. Some workers consider that the use of the term laterite should be discontinued, because of its genetic connotations and the uncritical application of the term to a wide variety of materials. The terms ferricrete or lateritic duricrust are sometimes preferred. (ii) Identifying and classifying lateritic materials. (iii) The mode of formation of the laterite; by in situ weathering, relative or absolute accumulation or by continual weathering and erosion of a long exposed landscape. The relationships of laterite to zones of mottled and bleached bedrock and sediment are critical. (iv) Determining the age of the laterite and the weathering processes responsible for its formation and its relationship to the age of the surface on which it rests. Critical investigations include determining the age of the underlying materials, the age of any overlying materials, whether the laterite has formed at the surface or subsurface and whether laterite formation is coeval with the development of the mottled and bleached zones. Attempts utilizing palaeomagnetism and other techniques, to try to resolve uncertainties in the numerical dating of ferricrete, have met with varying degrees of success. (v) The reliability of laterite and weathered, zones as palaeoclimatic indicators and their usefulness as morphostratigraphic markers. (vi) Identifying the topographic requirements for laterite formation and the reconstructions of former lateritized landscapes. Many workers have assumed former continuity of isolated present-day occurrences of laterite, whereas they may have formed only sporadically in relationship to local conditions. Many studies in Australia have assumed that laterite formed under seasonally dry humid tropical climatic conditions that resulted in intensive weathering processes during the Tertiary. It is believed that laterite formed as a uniform blanket over the landscape, so that present occurrences are erosional remnants of fossil laterite. Outside the humid tropics, laterite occurrences are considered as indicators of climatic change and / or continental drift. Many of these assumptions are open to alternative interpretations.