Dynamic Provenance Analysis of the Evolving Neogene Siwalik Succession in Eastern Himalayan Foreland Basin, Arunachal Pradesh: Implications on Paleo-Tectonism and Sedimentation History in the Arunachal Himalaya

The Neogene sedimentation in the Eastern Himalayan Foreland Basin (EHFB), Arunachal Pradesh, is thought to be driven by the interaction between the Transhimalayan and Himalayan sediments deposited by the antecedent paleo-Brahmaputra River (pBR) and Himalayan Rivers, respectively. However, the impact of episodic tectonism in the Arunachal Himalaya hinterland on the Siwalik sedimentation remains ambiguous. Dynamic provenance analysis of the Siwalik succession gives new insight about the paleo-tectonic history of the hinterland in relation to the Siwalik Foreland Basin sedimentation. The Dafla sediments (10–7 Ma) were primarily derived from the Tethyan and Greater Himalayan (GH) rocks through the south-flowing Himalayan drainage. While the southwest-flowing pBR brought a minor contribution from the Transhimalayan Arc (TA) into the Dafla Sea. After ~8 Ma, the Eastern Himalayan Syntaxis experienced accelerated exhumation, situated in northeast of the EHFB, and as a result, the west-southwest flowing axial pBR prograded rapidly and deposited the Subansiri sediments (~7–3.5 Ma) primarily sourced from the TA, GH, and Abor Volcanics. Around 5–4 Ma, the Main Boundary Thrust became active in the Arunachal Himalaya, leading to enhanced thrust loading in hinterland, resulted in increased accommodation space in foredeep area. This ensued in rapid progradation of the south-flowing transverse Himalayan drainage, chiefly eroding the Lesser Himalayan Gondwana rocks, and deposition of the fan deltaic Siji Formation (~3.5 to 2 Ma). Consequently, the axial pBR was retreated to northeast, and the contribution from the Transhimalayan source was diminished drastically. A new revised tectono-sedimentary evolutionary model of the EHFB is proposed.