ABSTRACT
Upper Siwalik sediments in northern Pakistan contain a well exposed record of palaeosols spanning most of the Pleistocene. Three sections at Mirpur, Rohtas, and in the Pabbi Hills on the margin of the Potwar plateau were studied. Palaeosols at all three sequences contain abundant pedogenic carbonate and soil organic matter (palaeohumus). The stable carbon isotopic composition of both of these phases indicates that nearly pure grasslands covered floodplains throughout the Pleistocene. Neutral to slightly alkaline values of soil pH, and leached zones dominated by Ca-smectite, chlorite and illite are also consistent with soils formed under grassland (mollisols). Stable oxygen isotopes in palaeosol carbonates are similar to those of modern soil carbonate in the area. The combined evidence strongly suggests that a monsoonal climate with moderate annual rainfall such as characterizes the eastern Potwar region today was in place throughout the Pleistocene. The carbon isotope chemistry of a post-Siwalik ( <400,000 yr) palaeosol and modern soils reflects the mixed thornscrub/grass cover typical of the broken hill country that developed after uplift and erosion of the Siwaliks.
