Pedogenesis and Mineralogy of Alluvial Soils from Semi-arid Southeastern Part of Rajasthan in Aravalli Range, India

Three representative alluvial soils were studied from Kothari river basin of Bhilwara district in southeast Rajasthan to assess degree of chemical weathering and pedogenesis. Morphological, geochemical, mineralogical and other analytical investigations were carried out. Soils were classified as Entisols and Inceptisols. These soils are mostly sandy with more than 50% of fine and medium sand fractions, silt to clay ratio more than 0.45 and little textural variation suggesting more uniform weathering. These soils are slight to strongly alkaline with high exchangeable sodium (>15%) and cation exchange capacity less than 10 cmol(+)kg −1 . Mineralogical investigations showed the dominance of micas and smectites in Pedon 1 (P1) and Pedon 2 (P2) and increase of smectites and micas in Bw3 horizon of P3 under strong alkalinity and high silica activity with limited lessivage. The low chemical index of alteration (CIA) in soils further indicated an incipient pedogenesis with a relative proportion of mica-smectite composition. The A-CNK-FM diagram shows abundance of CaO + Na 2 O + K 2 O as against Fe 2 O 3 + MgO components under limited leaching environment and chemical weathering. The results of bivariate plot of SiO 2 to (Al 2 O 3 + K 2 O + Na 2 O) indicated the past weathering which influenced by prevailing arid climate in the region.