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Item Geological and Petrological Evolution of the Lesser Himalaya between Mugling and Damauli, central Nepal(Institute of Science and Technology, Geology, 2014) Paudyal, KabirajThe Himalaya is divided into four tectonic zones as the Sub-Himalaya, the Lesser Himalaya, the Higher Himalaya, and the Tethys Himalaya from south to north, respectively. The Lesser Himalaya is a fold-and-thrust belt bounded by the Main Central Thrust (MCT) in the north and the Main Boundary Thrust (MBT) in the south and comprises autochthonous unit made up of Late-Precambrian to Early Paleozoic (?) low- to medium-grade metasedimentary rocks discordantly overlain by Proterozoic metamorphic crystalline rocks transported by thrusts. Although many authors have worked in central Nepal Lesser Himalaya, many parts still lacks large scale geological map and there are a number of problems and controversies on stratigraphic classification, tectonic interpretation and metamorphism. Present study was carried out in the central Nepal Lesser Himalaya between Mugling in the east and Damauli in the west covering both the autochthonous and allochthonous units. Main objectives of the study were to clarify the stratigraphic classification proposed by the previous authors, to prepare geological map and its crosssections, to use magnetic susceptibility for stratigraphic comparison, and to unravel the tectono-metamorphic history of the area. In the present study about 1000 square km area of the Lesser Himalaya between Mugling and Damauli was mapped in 1:25,000 scale. Lithostratigrpahy of the area was established and compared with the type-section by detailed route-mapping and preparation of columnar sections. Magnetic susceptibility was measured and analyzed in the autochthonous rocks along three sections in the Mugling-Damauli area and one section in the Malekhu area. Regional geological structures were measured and traced throughout the study area. Mesoscopic and microscopic structures were studied and analyzed both in the field and in thin sections. Metamorphic study was carried out using conventional petrographic microscope in thin sections. Illite and graphite crystallinities were measured ix by X-ray diffractometer and Raman Spectrocopy of Carbonaceous Materials was carried out using Raman Spectroscope. The study shows that the stratigraphic classification of the Lesser Himalayan autochthon proposed by Stöcklin and Bhattarai (1977) and Stöcklin (1980) need some modificaton. Possibly there exists no disconformity between the Dhading Dolomite and the Benighat Slate. Therefore, whole autochthonous rocks should be named as the Nuwakot Group (not the Nawakot Complex). The Anpu Quartzite, the Labdi Phyllite and the Banspani Quartzite are found to be lateral extensions of the same units as the Fagfog Quartzite, the Dandagaon Phyllite and the Purebensi Quartzite, respectively. Therefore, the former units do not exit as separate members. The Nourpul Formation is very extensive and is divisible into four members and two beds in the present study area. Magnetic susceptibility (MS) measurement in the Nuwakot Group rocks shows that each stratigraphic unit has its own MS pattern and range of MS values. This pattern is uniform in all sections of the present study area as well as in the type locality of the Nuwakot Group (i.e., Malekhu section). Therefore, it supports the present lithostratigraphic correlation made by field mapping in the Lesser Himalaya. The rocks of the allochthonous unit (Kahun Klippe) are named as the Tanahun Group and can be divided into three formations as the Gwaslung Formation, the Musimarang Formation and the Shivapur Schist, from bottom to top, respectively. The lithology of the Shivapur Schist is similar to that of the Raduwa Formation of the Kathmandu Nappe and Chaurijhari Formation of the Jajarkot Klippe. Therefore, the Gwaslung and the Musimarang Formations should be units older than the Raduwa Formation. It indicates that the Kathmandu Nappe, Kahun Klippe and Jajarkot Klippe are a part of a single crystalline thrust sheet and the basal thrust of the Kahun Klippe (the Dubung Thrust) is equivalent to the Mahabharat Thrust (MT). There is no lithological similarity between the rocks of the Kahun Klipe and that of the MCT zone and Higher x Himalaya. Therefore, the rocks of the klippe are probably units older than the Kunchha Formation deposited on top of the Higher Himalayan basement. The Mugling-Damauli area forms a part of a large duplex structure. The Dubung Thrust is the roof thrust, the MBT is the floor thrust, the Dewachuli Thrust is the imbricate fault and the Bhangeri Thrust is a back-thrust. The origin of the Lesser Himalayan crystalline nappes can be explained on the basis of single thrust model, i.e., the southward extension of the MCT. The area shows polyphase deformation (D xi 1 -D 5 ) and metamorphism (M 0 -M 3 ) as in the other parts of the Lesser Himalaya. At least two deformation events (D 1 and D 2 ) and one metamorphic event (M 0 ) are pre-Himalayan. The M 0 is normal burial metamorphism with grade increasing stratigraphically downwards and peak temperature reaching up to 370°C. The area suffered three deformation events (D 3 , D 4 and D 5 ) and three metamorphic events (M 1 , M 2 and M 3 ) after India-Eurasia collision. The second event (M 1 ) is Eohimalayan event causing garnet-grade prograde metamorphism in the Tanahun Group. This is pre-MCT event. The MCT-related Neohimalayan metamorphism (M 2 ) is inverted also in the low-grade zone of the Lesser Himalaya just below the Kahun Klippe. It is shown by both the illite and graphite crystallinity values. Key words: Lithostratigraphy, metamorphism, deformation, Kahun Klippe, root zone, central Nepal, Lesser Himalaya.Item Interconnectivity and water quality of shallow aquifer and the river system in the Kathmandu valley(Institute of Science & Technology, 2022-03) Bajracharya, RamitaThe groundwater and surface water are connected systems of single water resources. The connection condition can be noticed in different lands such as ponds, lakes, seas, and reservoirs but is mainly investigated at the stream reach scale. Interconnection of river-groundwater is a natural process that exchanges water between the river channel and water in subsurface areas. The exchange flow of water is dependent on the hydraulic conductivities of the river bed and aquifer sediments; the difference in water level in the river channel and adjacent groundwater; and the geometry of the river channel within the alluvial plain. The flow direction of water exchange is dependent on the hydraulic head between the river channel and the aquifer. The exchange process can be affected by anthropogenic activities such as sewage load in rivers, and a decline in the water table, which can alter the exchange condition, reduce connectivity, and contaminate aquifers chemically or biologically. Thus, the research related to interconnection is very essential to develop effective water resource management and policy as it can change the water quality and quantity of both water systems. However, there is a lack of such research in the case of Nepal. Hence, this study is focused to identify spatial and temporal interconnectivity between contaminated rivers of the Kathmandu Valley with peripheral groundwater. The isotopic analysis of δD and δ18O, chemical analysis of cations and anions along with sediment distribution patterns on the surface and subsurface were major utilized methods of the research. Hierarchical cluster analyses were used for grouping water samples into clusters depending on isotopic and chemical composition (Na+ and Cl-). The combination of river and groundwater samples into a single cluster indicated the presence of interconnection. For this research, Water samples were collected in August 2017 (wet) and Feb 2018 (dry). A total of 165 and 162 samples were collected from rivers, dug wells and shallow tube wells in the wet and dry seasons respectively. The isotopic composition (δD and δ18O) of the river presents a meteoric source for river discharge in both seasons. Samples from the Bagmati River, and Hanumante and Godawari Khola with enriched isotopic composition exhibit the possibility of evaporation during the dry season. The isotopic composition of groundwater shows spatially variable. Compared to GMWL and LMWL, groundwater is recharged through precipitation with some evaporation effect on samples. Interconnection condition of the groundwater and river water has been identified using HCA. River-groundwater interconnection is spatially and temporally variable. Wet season analysis shows that about 68% of sites are non-connected with river water which is especially located at the center of core urban areas of the Kathmandu Valley. The percentage of non-connection sites is reduced to 11% in the dry season showing a dominant influent condition (54%) as the exchange process. Only 9% of sites which shows non-connected in both seasons imply that the rivers of the Kathmandu Valley are connected with adjacent shallow groundwater. Chemical analyses of river water classify wet season as Ca-HCO3 type. Except for Godawari Khola and a few other river sections; others are changed to Na-K-HCO3, Ca-SO4, and Na-Cl-SO4 type, which indicates an increment of contamination during the dry season. The presence of a significant positive correlation between chemical ions indicates the influence of anthropogenic activities such as untreated municipal and industrial sewage discharge and leachate of solid waste disposal in river water. Additionally, a strong positive correlation of PO4--P with SO42- suggests the effect of fertilizer and pesticides used in the river’s peripheral agricultural land. Cluster analysis of dry season river water signifies that the Godawari Khola is the least polluted and the Hanumante Khola is a seriously contaminated river of the valley. The quality status of groundwater is determined by comparing it with the limit of NDWQS. The percentage of dug wells exceeding NH4+-N and EC becomes doubled (60.9% and 8.5% respectively) in the dry season, whereas dug wells exceeding pH has become increased up to ten times (10.4%). About 80% of dug wells exceed the limit of NH4+-N from the Manahara River and Hanumante and Balkhu Khola in the dry season showing severe anthropogenic contamination in the shallow aquifers. The presence of river-groundwater interconnection as a dominant influent condition again indicates that the higher contamination in shallow groundwater is the result of groundwater recharge by heavily contaminated river water during the dry season.Item