Highly mature sediments in the tropical monsoonal environment of southwestern India: an appraisal based on weathering indices

Abstract

Purpose This paper aims to examine the geochemical change experienced by laterites in Kerala, India, subjected to tropical monsoonal climate. These sediments are underlain by hard rock. The source rock characteristics have a major stake on the ultimate composition of sediments, as also the climatic conditions which an area experience. Design/methodology/approach Core samples have been obtained from several locations in a lateritic plateau. The upper portions of the borehole cores are composed of the lateritic hard cap, followed by lateritic soils. The soil samples were subjected to sediment texture analysis and XRF analysis (Bruker S4 Pioneer Sequential Wavelength-Dispersive XRF) for the determination of major elements ((in oxide form). Findings Major element geochemistry has revealed the following order of relative proportions of elements (in oxide form) SiO2 > Al2O3 > Fe2O3 > TiO2 >> Na2O > P2O5 > CaO > K2O > MgO > MnO. Even though the concentrations of SiO2, Al2O3 and Fe2O3 contribute 90% of major element chemistry, there is no significant correlation found for these elements within themselves or with others. Research limitations/implications Microscale movement of elements could not be characterised in this study. This requires access to an electron probe micro analyzer. Practical implications The practical implication of tropical weathering is that enhanced chemical leaching leads to movement of most elements out of the system, except for Al, leading to the possible formation of bauxite, or aluminous laterite. Social implications The weathered products in this study provide livelihood sustenance for many of the local households, through manual production of laterite bricks, which are used in construction. Originality/value The indices of the intensity of chemical alteration/weathering like chemical index of alteration (CIA), chemical index of weathering (CIW) and weathering index of parker (WIP) reveal that the sediments indicate intense weathering of the source area prior to being deposited in the present location. This indicates enhanced monsoonal activity in the provenance areas, than that obtained today.

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