Mineralogy and Geochemistry of the Calcretes in Alluvial Sediments from Pune, India

The calcretes in the alluvial sediments from Pune district, Maharashtra occur as hardpan, powdery, laminated, concretionary and pedotubule horizons. The calcretes are associated with clay minerals belonging to the smectite, chlorite and kaolin groups. The chemical analysis of the calcretes indicates that they are predominantly composed of calcium-carbonate and silica, (Cao: 33 to 37%, SiO₂ : 25 to 31%) with magnesium in very subordinate amounts. Trace elements present include Sr, Zr, V, Nb, Y, and Cs. On the basis of textural, mineralogical and chemical data, it is shown that the calcretes have resulted from two different processes, viz., by accumulation in the zone of fluctuation of groundwater tabie and by precipitation from percolating water during pedogenesis.