Tectonically-induced diversion of the Indus River west of the Salt Range, Pakistan

Abstract

Neogene and Quaternary molasse deposition at the west end of the Salt Range in the foreland fold-thrust belt of northern Pakistan produced an unusually thick upper Siwalik section near the Indus River. Here, Siwalik sedimentary rocks coarsen upsection to 1500 m thick stacked channel conglomerate deposits with a distant provenance similar to deposits forming the bed load of the modern Indus River. The Chisal Algad, an underfit stream separated from the Indus River by a tectonically-induced drainage divide, contains a bed load clast assemblage resembling that of the Indus River. The Indus channel migrated eastward, abandoning the Chisal Algad and leaving high terrace deposits of Indus gravels unconformably overlying tilted Siwalik sedimentary rocks north of Shakardarra. Uplift accompanying thrust faulting and transpression in the right-slip Kalabagh fault zone tilted a block measuring 15 km east-west by 30 km north-south. The block has been incised by juvenile consequent drainage toward the Indus River. The Indus River was diverted eastward in the last 0.5 Ma and now occupies the lower part of the Soan River system.