Systematic study of the eastern Nepal Himalaya was started after 1950 when Nepal opened up for foreigners. Thereafter, several geological studies have been carried out in the Arun-Tamor region of eastern Nepal Himalaya. The Tibetan-Tethys sedimentary sequence, the Higher Himalayan amphibolite to granulite facies metamorphic crystalline sequence, the Lesser Himalayan sedimentary and greenschist facies metasedimentary sequences, and the Siwalik foreland molassic sedimentary sequence are the four major tectonic units of this area. The individual nomenclature schemes of stratigraphic units, the correlational dispute, the positions and interpretations of regional geological structures are some examples that have created controversies regarding the lithostratigraphy and structural arrangements. The difference in age and genesis of the Main Central Thrust and its effects in the metamorphism of the eastern Nepal Himalaya are the exemplification of the contradiction in the interpretation of the tectonometamorphic history. There is a gap in research in the tectonics and episodic metamorphic evolution of the area owing to the bare approach in the microstructural and geochronological investigation. Future investigations should be focused on solving the above mentioned controversies and narrowing down the research gaps in tectonic and metamorphic evolution.
Geological mapping was carried out in the outer part of the Lesser Himalaya in the Barahakshetra – Tribeni area of east Nepal along the Arun River valley. A revised and updated tectono-lithostratigraphic scheme of the area along with detailed description of each unit and their comparison with central and west Nepal has been presented in this work. The area is divided into three tectonic units named as the Chimra Thrust Sheet, the Dharapani Thrust Sheet and the Tribeni Paraautochthon from north to south, respectively, separated by the Chimra Thrust and the Dharapani Thrust. The rocks of the Chimra Thrust Sheet consist the Pre-Cambrian Phongsawa Group and is divided into the Mulghat Formation, Okhre Formation, Jyamire Gneiss and Belhara Formation, from bottom to top, respectively. The Jyamire Gneiss is comparable to the Ulleri Augen Gneiss and other formations are equivalent to the lower part of the Kuncha Formation. The Dharapani Thrust Sheet, comprising Pre-Cambrian Bhendetar Group, is subdivided into the Chiuribas Formation, Sangure Quartzite and Karkichhap Formation, from bottom to top, comparable with the upper part of the Kuncha Formation, Fagfog Quartzite and Dandagaon Phyllite, respectively. The Tribeni Paraautochthon is divided into the Late Pre-Cambrian Lukuwa Dolomite unconformably overlain by the Gondwana and post-Gondwana rocks of the Barahakshetra Group. The Barahakshetra Group is divided into the Kokaha Diamictite and Baraha Volcanics, Sapt Koshi Formation and Tamrang Formation, from bottom to top, comparable with the Sisne Formation, Taltung Formation and the Dumri Formation, respectively.
Geological mapping was carried out in the Chatara–Barahakshetra area of east Nepal. The Siwalik of the Chatara–Barahakshetra area is divided into the Lower Siwalik and the Middle Siwalik. Each unit is further subdivided into lower and upper members. The Central Churia Thrust is overturned in the study area. Highly deformed Siwalik contain several outcrop-scale as well as a large-scale folds. Bulletin of Department of Geology, vol. 20-21, 2018, pp: 49-58
Increasing evidence of changing climate patterns is being observed, and the impact of this change on groundwater has a direct impact on the livelihood and economy of the region. The research focuses on the impacts of global temperature increase and changing precipitation on the groundwater resources of part of the Himalayan river system. The spatial and temporal variations of the hydro-meteorological data of the Kankai River Basin in East Nepal were analyzed using non-parametric Mann–Kendall tests and Sen’s Slope methods, whereas CanESM2 was used to predict the future precipitation scenarios, and an attempt has been made to evaluate the possible impacts on groundwater systems in the region. The temperature shows a significant warming trend (0.14–0.64 °C/decade); however, the precipitation trends suggest remarkable variation mostly at higher elevation. The average annual precipitation suggests a decrease of 1.82 mm/year and a similar decrement has been projected for the future. The groundwater in the region has been influenced by the changing climate and the condition may further be exaggerated by reduced recharge and increased evapotranspiration. This understanding of the impacts and climate scenarios will help the planners with better adaptation strategies, plans, and programs for a better society.
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