Channel morphology, hydrology and geomorphic positioning of a Middle Miocene river system of the Siwalik foreland basin, India

Abstract

AbstractSystematic lithofacies, palaeocurrent, palaeomorphological and palaeohydrological analyses have provided detailed information about a hitherto unstudied river system of the Siwalik foreland basin of the Himalaya. Three distinct lithofacies associations, each representing a specific depositional setting, have been identified and named as ‘Facies Association A’, ‘Facies Association B’ and ‘Facies Association C’. The ‘Facies Association A’ comprises pebbly sandstone, cross-bedded sandstone, ripple-laminated sandy siltstone and bioturbated mudstone lithofacies and represents deposits of a braided channel. The ‘Facies Association B’ comprises cross-bedded sandstone, bioturbated mudstone, fine sandstone–mudstone alternation and lensoid to prismatic sandstone lithofacies and represents deposits of a channel, natural levee, crevasse-splay and flood plain of a meandering stream. The ‘Facies Association C’ comprises mottled siltstone–mudstone heterolith and fine sandstone lithofacies and represents deposits of the upland interfluve region. The braided stream had a maximum depth of 4.15 m, maximum width of 305 m and maximum discharge of 7045 cumec, whereas the meandering stream had a sinuosity of 1.26, maximum depth of 3.71 m, maximum width of 180 m and maximum discharge of 4070 cumec. The area had a regional radial outward flow pattern, but dominantly towards the SSW. However, the braided river had a bimodal flow pattern due to an active basement-high-induced bend along its course. A comparison of the sediment characters and morphological and hydrological parameters of these streams with those of the modern rivers of the Ganga (Gangetic) basin has enabled us to infer that this river system was located in the medial-distal megafan-interfan setting of the basin.