Qualitative and quantitative analysis of river systems in the Lower Siwalik sequence has enabled characterization of channel patterns, river metamorphosis and resulting sandstone body evolution in time and space. Processes related six lithofacies repeat to generate 8-10 m thick multistoried sandstone complexes deposited in perennial channel belts. Based on lateral mapping of the sandstone bodies, the surfaces of genetic significance ranging from 3 rd , 4 th and 5 th order, suggest presence of meandering, braided and anastomosing river patterns that were responsible for the Lower Siwalik sedimentation. Variation in local base-level in response to allogenic factors including climate and tectonics forced river systems to acquire different patterns. Eustasy seems to control large-scale basin level changes.Quantitatively reconstructed morphological parameters and their comparison with modern and ancient analogues, supported by other independent evidences such as stratigraphical position of sandstone bodies in vertically measured columns and mineralogical characteristics of channel sandstones, enabled to decipher the geomorphic positioning of the Lower Siwalik channels in distal parts of megafan and interfluve areas within the foreland basin setting.

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In Kameng Valley of Arunachal Pradesh, the crystalline rocks of Se La Group of Higher Himalaya are thrust over the Lesser Himalayan rocks of Dirang Formation, Bomdila Group along the Main Central Thrust and exhibit well preserved structures on macro-to microscopic scales. Detailed analysis of structures reveals that the rocks of the area have suffered four phases of deformation D 1 , D 2 , D 3 and D 4 . These structures have been grouped into (i) early structures (ii) structures related to progressive ductile thrusting and (iii) late structures. The early structures which developed before thrusting formed during D 1 and D 2 phases of deformation, synchronous to F 1 and F 2 phases of folding respectively. The structures related to progressive ductile shearing developed during D 3 phase of deformation, when the emplacement of the crystalline rocks took place over the rocks of Dirang Formation along the Main Central Thrust. Different asymmetric structures/kinematic indicators developed during this ductile/brittle-ductile regime suggest top-to -SSW sense of movement of the crystalline rocks of the area. D 4 is attributed to brittle deformation. Based on satellite data two new thrusts, i.e. Tawang and Se La thrusts have been identified parallel to Main Central Thrust, which are suggestive of imbricate thrusting. Strain analysis from the quartz grains of the gneissic rocks reveals constriction type of strain ellipsoid where k value is higher near the MCT, gradually decreases towards the north. Further, the dynamic analysis carried out on the mesoscopic ductile and brittle-ductile shear zones suggest a NNE-SSW horizontal compression corresponding to the direction of northward movement of Indian Plate.

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