Abstract:
A petrography–geochemistry-based evaluation of
the provenance of the sandstones of the Tertiary Middle
Siwalik Subgroup in the Lish River Valley, West Bengal, is
presented. The framework grains in the sandstones suggest
mixing of sediments from spatially separated gneissic, quartzitic
and phyllitic source rocks. Modal values of different
framework minerals suggest that recycled sediments in an
orogenic setting were deposited in the Middle Siwalik basin
in the area. The major and trace element ratios suggest dominantly
felsic input and mixing with subordinate basic material
in an upper continental crustal setup. The major and trace
element data also indicate that rocks of a passive margin setting
acted as the source to the sediments. The present paper
postulates that the Middle Siwalik sediments were derived
from pre-Himalayan gneissic and metabasic rocks of an erstwhile
passive margin setting and presently forming the Higher
and Lesser Himalaya, respectively.
