Sedimentary facies and soft-sediment deformation structures in the late miocene-pliocene Middle Siwalik subgroup,eastern Himalaya,Darjiling District,India |
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Authors: | " target="_blank">Abhik Kundu " target="_blank">Abdul Matin " target="_blank">Malay Mukul " target="_blank">Patrick G Eriksson |
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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,Powai, Mumbai,India;4.Department of Geology,University of Pretoria,Pretoria,South Africa |
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Abstract: | The Himalayan fold-and-thrust belt has propagated from its Tibetan hinterland to the southern foreland since ∼55 Ma. The Siwalik
sediments (∼20 - 2 Ma) were deposited in the frontal Himalayan foreland basin and subsequently became part of the thrust belt
since ∼ 12 Ma. Restoration of the deformed section of the Middle Siwalik sequence reveals that the sequence is ∼325 m thick.
Sedimentary facies analysis of the Middle Siwalik rocks points to the deposition of the Middle Siwalik sediments in an alluvial
fan setup that was affected by uplift and foreland-ward propagation of Greater and Lesser Himalayan thrusts. Soft-sediment
deformation structures preserved in the Middle Siwalik sequence in the Darjiling Himalaya are interpreted to have formed by
sediment liquefaction resulting from increased pore-water pressure probably due to strong seismic shaking. Soft-sediment structures
such as convolute lamination, flame structures, and various kinds of deformed cross-stratification are thus recognized as
palaeoseismic in origin. This is the first report of seismites from the Siwalik succession of Darjiling Himalaya which indicates
just like other sectors of Siwalik foreland basin and the present-day Gangetic foreland basin that the Siwalik sediments of
this sector responded to seismicity. |
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