Depositional environment and provenance of Middle Siwalik sediments in Tista valley, Darjiling District, Eastern Himalaya, India

Abstract

The frontal part of the active, wedge-shaped Indo-Eurasian collision boundary is defined by the Himalayan fold-and-thrust belt whose foreland basin accumulated sediments that eventually became part of the thrust belt and is presently exposed as the sedimentary rocks of the Siwalik Group. The rocks of the Siwalik Group have been extensively studied in the western and Nepal Himalaya and have been divided into the Lower, Middle and Upper Subgroups. In the Darjiling-Sikkim Himalaya, the Upper Siwalik sequence is not exposed and the Middle Siwalik Subgroup exposed in the Tista river valley of Darjiling Himalaya preserves a ∼325 m thick sequence of sandstone, conglomerate and shale. The Middle Siwalik section has been repeated by a number of north dipping thrusts. The sedimentary facies and facies associations within the lithostratigraphic column of the Middle Siwalik rocks show temporal repetition of sedimentary facies associations suggesting oscillation between proximal-, mid-and distal fan setups within a palaeo-alluvial fan depositional environment similar to the depositional setup of the Siwalik sediments in other parts of the Himalaya. These oscillations are probably due to a combination of foreland-ward movement of Himalayan thrusts, climatic variations and mountain-ward shift of fanapex due to erosion. The Middle Siwalik sediments were derived from Higher-and Lesser Himalayan rocks. Mineral characteristics and modal analysis suggest that sedimentation occurred in humid climatic conditions similar to the moist humid climate of the present day Eastern Himalaya.

Deltaic coastline of the Siwalik (Neogene) foreland basin: evidences from the Gish River section, Darjeeling Himalaya

“…The abundance of wave‐, combined flow‐ and storm‐generated structures (~48% of the 1.3 km of the logged succession) and occurrence of trace fossils of marine affinity and brackish water tolerant palynospecies throughout the succession indicate that the Siwalik rocks exposed in the Gish River area were strongly influenced by marine depositional processes and are unlikely to represent an exclusively continent interior, upland, alluvial fan‐braided stream system as inferred by earlier workers (Banerjee and Banerjee, ; Kundu et al ., , ; Mandal et al ., ).…”

“…In the Siwalik succession of Eastern Himalaya, the presence of thick dark grey mudstone (Karunakaran and Ranga Rao, ), palynoassemblages and trace fossils of brackish water affinity (Mitra et al ., ; More et al ., ), abundance of wave generated structures and a complex polymodal palaeocurrent have been reported (Taral, ). The existing depositional models of upland alluvial fan or fluvial channel–interchannel setting for Siwalik rocks of the Tista valley (Banerjee and Banerjee, ; Kundu et al ., , ; Chakraborty et al ., ; Mandal et al ., ) do not explain any of these peculiarities of the Siwaliks of Eastern Himalaya. A sedimentological analysis of the succession is critical in understanding the pattern of the drainage network, palaeogeographic setting and tectonic evolution of the foreland basin (Bera et al , ; Leeder, ; Chirouze et al , ; Bracciali et al ., ).…”

Detrital zircon U–Pb geochronology of the Siwalik Group of the Nepal Himalaya: implications for provenance analysis

“…In the Kangra sub-basin of northwestern Indian Himalaya, Kyanite and Sillimanite first appeared at 13 and 8 Ma, respectively, indicating a slow exhumation of the HH (Najman 2006 and reference therein). A petrographic study of the Middle Siwalik in the eastern Himalaya shows that the dominant source of the sediments was from HH and LH (Kundu et al 2012). A study by Critelli and Garzanti (1994) along the northeast Pakistan has revealed that the HH was carried southward during Middle Miocene after reactivation of the MCT.…”

Sedimentary environment and geomorphic development of the uppermost Siwalik molasse in Kumaun Himalayan Foreland Basin, North India

“…A large number of sequences of Upper Siwalik sediments from Pakistan (e.g. Keller et al, ; Pilbeam et al, ; Opdyke et al, , ; Barry et al, ; Johnson et al, , ; Tauxe and Opdyke, ; Flynn et al, ), NW India (Sahni and Khan, ; Azzaroli and Napoleone, ; Johnson and McGee, ; Tandon and Naug, ; Tandon et al, ; Kumar and Tandon, ; Ranga Rao et al, ; Sangode et al, , ; Thomas et al, , ; Kumar et al, , b, ), eastern Himalayan foothills (Srinivasan, ; Luirei and Bhakuni, ; Kundu et al, ; Chakraborty et al, ) and Nepal (Munthe et al, ; Tokuoka et al, , , ; Corvinus, , ; Appel et al, ; Corvinus and Nanda, ; Gautam and Appel, ; Kotlia and Mathur, ; Rösler et al, ; Gautam and Rösler, ; Nakayama and Ulak, ; Gautam and Fujiwara, ; Corvinus and Rimal, ; Ulak and Nakayama, ; Ulak, , ) have been studied particularly from the view‐point of palaeomagnetic dating, sedimentary features and depositional environment, suggesting that the thickness of the Upper Siwalik varies laterally across the foreland basin exhibiting an increase in conglomerates towards the MBT. The boundary between the Pinjor and Boulder Conglomerate formations in the Indian Siwalik is placed at ca.…”