Depositional environment and provenance of Middle Siwalik sediments in Tista valley,Darjiling District,Eastern Himalaya,India |
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| Authors: | ABHIK KUNDU ABDUL MATIN MALAY MUKUL |
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| Institution: | 1.Department of Geology,Asutosh College,Kolkata,India;2.Department of Geology,University of Calcutta,Kolkata,India;3.Department of Earth Sciences,Indian Institute of Technology Bombay,Mumbai,India |
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| 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 fan-apex 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. |
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