Petrography and Clay Mineralogical Study of the Siwalik Group of Rocks Exposed along Pasighat-Mariyang Road Section, East Siang District, Arunachal Pradesh, Northeast India
Ananya Chutia, Chaitra Dhar Taye, Jagriti Daimari, Debasish Chutia
Abstract
Abstract The Neogene (Mio-Pliocene) molassic sediments occur as a linear belt along the foot hills of Arunachal Pradesh, are designated as the Siwalik Group. Petrography, heavy mineral and clay mineralogical characteristics of these rocks exposed along Pasighat-Mariyang road section, East Siang district, Arunachal Pradesh, India is presented here. These massive and well bedded rocks are detached from alluvium by HFT and remarkably from Yinkiong Group of rocks by MBT. The present study reveals the presence of lower as well as middle-upper Siwalik in the study area. Petrographic study of the sandstones has shown that these rocks are mainly sub-arkose and sub-lith-arenite with lithic and feldspathic greywacke in subordinate amount, which are medium to coarse grained and composed mainly of quartz, feldspar, mica and rock fragments as their detrital constituents. Argillaceous and siliceous matrix as well as argillaceous, carbonate and siliceous cement are binding the framework grains. These sediments were derived mainly from middle to upper grade metamorphic rocks. During deposition these rocks have undergone shallow depth as well as deeper level diagenesis and the climate prevailed was humid and tropical.