Abstract:
The Mio-Pliocene Middle Siwalik Subgroup, in the
Lish River Section in the Darjiling District of the Eastern
Himalaya, consists of sandstone, mudrocks, heterolithic
units and conglomerates preserving six distinct
associations of soft-sediment deformation structures at
different stratigraphic levels. The foreland basin
sediments of the Himalayan orogen were deposited in
alluvial fan settings. Deformation structures present are:
folds of variable geometry, pseudonodules, water escape
features, flame structures and chaotic laminae.
Liquefaction and/or fluidization of sediments in the soft
state are inferred to have been responsible for the origin
of these structures. Both the depositional palaeoenvironment
and seismic tremors generated due to
thrusting activities in the hinterland situated to the north
of the then Middle Siwalik basin contributed to triggering
the liquefaction/fluidization and creation of the softsediment
deformation structures within the Middle
Siwalik sediments.
