Pakistan Research Repository                                                                

THE PLEISTOCENE GEOMORPHOLOGY OF THE SOUTH-EASTERN PART OF THE PESHAWAR VALE

Peshawar valley is located on the junction of the Indo-Pakistan platform and the Asian shield. The geological evolution of the valley has taken, a long time period, of about-20 myr, from the middle of the Cenozoic, to the beginning of the Pleistocene. However, the final configuration was achieved, during the later phases of the Himalayan orogeny. Since then, it has passed through several phases of erosion and deposition. The deposits on the surface as well as in the sections preserve a good record of environmental changes. The study area lies in the south-eastern part of the valley. Its surface deposits include fan-gravels, river-gravels, medium-grained sand, thick deposit of loess and fine alluvium. The deposits on the surface reflect the preparation of deep regolith on the Attock-Cherat range, due to the growth of vegetation, in pluvial environment, and its subsequent deposition in the foot of the mountain range, as alluvial fans, in moderately arid to semi-arid climate. The deposits also record flood of low to moderate magnitudes, and periglacial environment, during the pleistocene period. On the basis of stratigraphical investigations, five pluvial and interpluvial phases have been identified. First, second and fourth pluvial phases seem to be cold and humid, during which, vegetation growth took place on the Attock-Cherat range, and deep regolith was prepared. Third and fifth phases were too cold and dry for the growth of vegetation. Periglacial environment prevailed in the valley, during which loess was deposited in the plain as well as over the surrounding mountains. The erosion of the weathered zones occurred in warm-dry interpluvial phases. Subsequent to the decay of vegetation cover and rapid tectonic uplift of the Attock- Cherat range, the material, exposed, was carried down, and deposited at the base of the mountain range forming alluvial fans. Four phases of fan formation have been identified, There are also evidence to show that Peshawar valley was transformed into a lake twice, perhaps, due to -the damming of the Indus river, below Khwara valley. It occurred during the second and fourth pluvial phases, Siltstone beds of enormous thickness, were formed in the lake environment. A variety of river deposits, including, sand, gravel-conglomerate, huge boulders and erratics, and fine alluvium are preserved in the area. Sandstone and gravel-conglomerate have been deposited on the siltstone beds, by the Kabul and Indus rivers, during the second and fourth pluvial phases. The fine alluvium was deposited by the Kabul river and its tributries, in the flood plains, during the Holocene. The deposits mentioned, have also been eroded and deformed due to intermittent tectonic uplift, during the Pleistocene period.

INTRODUCTION