Observations on Genesis and Evolution of Arid Zone Soils

Dunes in western Rajasthan are devoid of any pedogenic activity except for weak segregation of free alkaline earth carbonates. Occurrence of accumulative interdunes, however, suggests that the dunes are not a recent phenomenon and belong to the aeolian activity reported to have taken place 10,000 years B.P. The soils on hummocky, aggraded, old, alluvial plains show weak argitlisation, but a distinct illuvial accumulation, partly as crystalline concretions, of free carbonates. Degree of development of concretionary horizon together with some radio-carbon assay, suggests that the landscape belongs to at least Late Pleistocene. The old flat-plains owe their characteristics to influence of fine sedimentary rocks. These soils and landscape are also old but are almost devoid of deflation evidences. High silt and clay content apparently provided the required strength and stability against aeolian activity. The soil in situ and proluvial landforms are distinguished by presence of gravel and transition to sub-strata. Findings tend to show that though fluctuation may have taken place in wind activity and rainfall, general aridity has existed at least from Late Pleistocene.