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Himalayan Geology, Vol. 32
(2), 2011, pp. 123-135, Printed in India
Detrital modes of Late Neogene Siwalik Sandstone of the Ramganga Sub basin,
Kumaun Sub- Himalaya: implication for the source area tectonic history
POONAM JALAL1*, SUMIT K. GHOSH2, Y.P. SUNDRIYAL1
1Department of Geology, H.N.B. Garhwal University, Srinagar (Garhwal),
India
2Sedimentology Group, Wadia Institute of Himalayan Geology, Dehra
Dun -248001, India
*Email: jalal.poonam@gmail.com
Abstract: The fluviatile succession of Siwalik Group of the Himalayan
Foreland Basin (Siwalik Group) represents one of the largest and active
basins that have recorded the various manifestation of source area tectonics
The distinct grey, salt and pepper textured 7.7-4.5 Ma sandstone of the
Baliagad -Gaula River (BGR) Section, Ramganga sub-basin is characterized by
its framework components as coarse-medium- to fine- grained matrix- poor
lithic to sublithic arenite and matrix- rich quartz wacke. The textural and
compositional variability of the sandstone suggests a mixed provenance
comprising abundant metamorphic subordinate sedimentary and igneous. The
quartz fabric and the metamorphic ranks of rock fragments hints towards the
presence of low to medium grade metamorphic source.
The temporal variability of sandstone types, Qp/Qm ratio and relative
increase of metamorphic rock fragments suggests tectonic activity in the
source area at 6.25 Ma and 5.15 Ma. The quartz fabric study further adds
that the source area had suffered a temperature of at least 500ºC. Three
hinterland thrust, namely the Main Boundary Thrust (MBT), Ramgarh Thrust (RT)
and Almora Thrust (AT) played an important role for the supply of detritals
to the depocentre. The present study infers the existence of crystalline
nappes of the Ramgarh and Almora prior to 7 Ma. The MBT is responsible for
exhuming the Lesser Himalaya after 5 Ma.
Keywords: Source area, Siwalik Sandstone, Late Neogene.
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