The increasing frequency of landslides has become a matter of concern in Nagaland, a north‐eastern state of India. Noklak town, the administrative headquarter of the Noklak district in the eastern part of Nagaland bordering Myanmar, is also affected by slope stability issues. A major landslide in 1980 caused major damage to parts of the township. The problem has grown in magnitude and influence over the last four decades, damaging an area of about 1.84 km2 and several households. Slope movements have caused immense distress to the local populace by posing a constant threat to nearly one‐fourth of the town's built‐up area, roads, and cultivated tracts. Surface instability has also hampered India's Act East policy with South‐east Asian countries by disrupting the sole motorable route to the International Trade Centre at Dan (Pangsha), between India and Myanmar. A landslide susceptibility map (LSM) was generated using the Bivariate Yule coefficient (Yc) method. The LSM delineates the study area into three categories, with 23%, 23%, and 54% in high, moderate, and low susceptible zones, respectively. This was superimposed with elements such as buildings, population, roads, and cultivated tracts to assess the effects of landslides on the population and infrastructure. From the present study, it is estimated that 334 buildings, 1235 people, 2.99 km of roads, and 8 ha of cultivated landfall lie within the moderately and highly susceptible zones. Considering the rapid developmental activities that will ensue with the recent upgradation of the subdivision to that of the district, the data generated will be useful for urban sprawl and land use planning, to minimise and mitigate the loss of life and property due to landslides.
The Oligocene Laisong Formation in the Naga Schuppen Belt is coal bearing along the Dimapur-Kohima Road section, Nagaland. The coals are sulphurous and classified as lignite to sub-bituminous 'C' based on various rank parameters. The coals are dominantly composed of vitrinite followed by inertinite and liptinite in order of abundance. The coals have high-quality Type III kerogens derived mainly from angiosperm plants. The richness and quality of organic matter in the coal is excellent to act as a petroleum source rock. Most of the maturity parameters indicate that maturity ranges from immature to early mature. The biomarker parameters and facies critical maceral associations point to deposition of the coal-bearing strata in non-marine/ terrestrial depositional environment under moist hydrodynamic conditions, possibly in an upper delta plain environment. However, the high sulphur content of the coal points to deposition in a lower delta plain environment. Comparison with other Palaeogene coal deposits of the same sedimentary basin shows that the Laisong coals contain lesser amount of liptinite macerals and much higher amount of sulphur than these deposits. All these deposits are of similar rank, however, the Laisong coals show marginally low thermal maturity from the viewpoint of hydrocarbon generation.
Vertical Electrical Sounding (VES) technique which employs the Schlumberger depth sounding method was used to investigate the subsurface conditions at the landslide in Perizie colony, Kohima. The interpretation of the VES curves shows differing lithology consisting of weathered shales with associated clay, which is considered an important factor for slope instability. The shear strength of the slope materials, including the country rocks and the soil cover, is also significantly reduced and easily detached due to the effects of weathering and erosion, causing the landslides. Three to six possible geo-electric layers are delineated from the variations in the resistivity values, with the lithologies consisting of topsoil followed by alternate layers of weathered and fractured rocks of varying thickness. The analysis also points to the presence of a weak zone at a depth of about 10 m, which is not apparent from the surface. The formation of groundwater aquifers in the fractured zones indicates high risk for slope failure as this accelerates the weak country rocks to weather. The results obtained by this study correspond well with the available borehole data of the area.
The Jurassic‐Cretaceous chert of the Naga Hills Ophiolite (NHO) is tectonically juxtaposed with the mafics (mostly basalts) and ultramafics along the Indo‐Myanmar Ranges (IMR), which constitute the southeastern extension of the Indus‐Yarlung‐Tsangpo Suture. Petrographic and geochemical studies were taken up to determine their origin and paleo‐oceanic depositional environments. Cryptocrystalline quartz is intimately mixed with iron oxides and clay minerals containing poorly preserved radiolarians. Geochemical signatures indicate a predominantly biogenic origin for the NHO cherts, which were derived from radiolarians and other siliceous microfossils. Rare earth elements and trace element abundances indicate predominant contribution by scavenging from seawater with the minor influence of low‐temperature hydrothermal activity. Most of the NHO cherts were deposited in an open ocean basin where oxic conditions prevailed. Geochemical signatures endorsed by field relations of chert, pillow basalts, and limestone within the oceanic plate indicate that chert formation continued in the vicinity of oceanic islands. Organic matter played a pivotal role in regulating oxic‐anoxic conditions during deposition, as evidenced by redox‐sensitive trace elements. These cherts, envisaged to have been originally part of the Tethys, were tectonically emplaced during the Middle Eocene. They now constitute part of the NHO along the IMR.
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