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Red Beds |
Department of Geography, Kings College, Strand, London WC2R 2LS
This paper describes the pedological processes, including that of reddening, in latosol formation in dune sands on humid tropical coastlines. A time-scale is established for these processes in South-east India, Sri Lanka and the Natal Province of the Republic of South Africa. Weathering in situ of the dune sands has occurred since their deposition in all three locations. Evidence from thin section and TEM analyses shows that detrital addition of clay minerals and iron oxides has been negligible. The major pedogenic processes (as shown by thin section, SEM, TEM, XRD and chemical analyses) in the formation of the latosols in the field areas are: weathering of garnet, feldspar, hornblende and opaque minerals; formation of kaolinite and illite clay minerals; oxidation of iron to haematite, and loss of carbonate and partial removal of silica from weathered horizons, followed by their deposition lower down the profile in some cases. Dating of the red latosols (2.5 YR 4/6-10R 4/8), radiometrically and using archaeological evidence, indicates that formation to depths of 10 m has taken place in under 20,000 years in the coastal dune sands in the field areas. It is suggested that reddening of desert sands by mineral breakdown could take place on time-scales that are much shorter than has previously been assumed.
