Evolution of Miocene-Pliocene fluvial paleoenvironments in eastern Potwar Plateau, northern Pakistan

The Neogene Siwalik Group in the Mahesian and Rohtas areas of northern Pakistan, was studied in order to reconstruct the evolution of depositional environments and the controls on this evolution.;The following vertical variations are observed within the Siwalik Group: (1) major sandstone bodies coarsen from fine to medium sandstone through the Nagri Formation, there is abrupt fining at the base and top of the Dhok Pathan Formation, followed in the Soan Formation by increasing grainsizes of all facies; (2) the proportion of major sandstone bodies generally increases upwards in the Nagri Formation; however, variation in grainsizes and proportion of major sandstone bodies are not correlated in the Dhok Pathan and Soan Formations; (3) thicknesses of major sandstone bodies increase upwards in the Nagri Formation, with decrease at the base and top of the Dhok Pathan Formation; (4) decrease in sedimentation rate from 0.34 to 0.25 to 0.21 mm/yr in the Nagri, Dhok Pathan and Soan Formations, respectively. Basin-wide increase in sediment accumulation rate, grainsize, proportion of major sandstone bodies, and changes in their composition in the Nagri Formation (C5N) are associated with tectonic uplift of the Himalayas, progradation of wedges or lobes of sediment to the south and southeast and increasing depositional slope.;The major sandstone bodies are composed of storeys, stacked both vertically and laterally and represent either single or superimposed channel-belt deposits. Internal characteristics of the storeys indicate deposition as bars and channel fills within low sinuosity (1.1-1.2) braided channels with braiding index of 2 or 3. Individual channel segments had widths of 167-500m, maximum bankful depths of 7-17m, bend wavelengths of 1.4-4 km and bankful discharges of 300-1300 m...