The magnetostratigraphy, fission-track dating, and stratigraphie evolution of the Peshawar intermontane basin, northern Pakistan

The Peshawar basin is situated along the junction of the northern margin of the IndoGangetic foredeep and the southern margin of the Hindu Rush-Himalayan Ranges. During the late Cenozoic, southward encroachment of tectonic disruption into the foredeep terminated molasse deposition and delineated the Peshawar intermontane basin through uplift of the Attock Range along the southern margin of the basin. In this study, magnetostratigraphy, fission-track dates on volcanic ashes, and stratigraphic data are used to define the chronologic and stratigraphic evolution of the basin. Following a late Miocene to Pliocene interval of folding and thrusting of the preexisting molasse sediments, deposition began in the Peshawar basin by at least 2.8 m.y. ago. Subsequently, >300 m of basin-filling sediments accumulated at rates averaging IS cm/1,000 yr. Northward progradation of alluvial-fan deposits from the uplifted basin margin had begun by -2 .6 m.y. ago and continued at an inferred rate of 2 cm/yr. Proximal to the Attock Range in the south, alluvial-fan fades persisted until -0 .6 m.y. ago. Contemporaneous sediments closer to the basin center demonstrate the presence of rapid facies transitions to extensive floodplain and shallow-lacustrine depositional environments. Widespread intermontane-basin sedimentation was terminated by accelerated uplift of the Attock Range after ~0.6 m.y. ago. Subsequently, during the Brunhes chron, catastrophic floods have periodically inundated the Peshawar basin. Continuing tectonic deformation of the basin is indicated by uplifted flood deposits, offset terraces, and modern seismicity.