Petrography and geochemistry of the Middle Siwalik sandstones (tertiary) in understanding the provenance of sub-Himalayan sediments in the Lish River Valley, West Bengal, India

摘要

A petrography–geochemistry-based evaluation ofthe provenance of the sandstones of the Tertiary MiddleSiwalik Subgroup in the Lish River Valley, West Bengal, ispresented. The framework grains in the sandstones suggestmixing of sediments from spatially separated gneissic, quartziticand phyllitic source rocks. Modal values of differentframework minerals suggest that recycled sediments in anorogenic setting were deposited in the Middle Siwalik basinin the area. The major and trace element ratios suggest dominantlyfelsic input and mixing with subordinate basic materialin an upper continental crustal setup. The major and traceelement data also indicate that rocks of a passive margin settingacted as the source to the sediments. The present paperpostulates that the Middle Siwalik sediments were derivedfrom pre-Himalayan gneissic and metabasic rocks of an erstwhilepassive margin setting and presently forming the Higherand Lesser Himalaya, respectively.