Magnetic susceptibility studies of the upper Albian-Danian sediments of Cauvery basin,south India

The Cauvery basin of the Indian Peninsular shield, formed during the fragmentation of the Gondwana Supercontinent, continued to evolve until the end of Neogene through rift, pull-apart, shelf sag and tilt processes. The basin witnessed many cycles of transgression, regression, erosion and deposition. A more or less complete succession of upper Cretaceous–Paleocene sediments is exposed in the Ariyalur–Pondicherry depression of the basin. Anisotropy of magnetic susceptibility (AMS) technique is applied in an attempt to examine the depositional and eustatic conditions prevailed during the formation of these sedimentary sequences. AMS results point to the sedimentation history dominated by marked sea level changes with several phases of transgression and regression. The sedimentation occurred mainly in a shallow epicontinental sea which has been punctuated with terrigenous supply more often. Greater utility of magnetic fabrics is suggested as a tool to trace fluvial responses to tectonic and climatic changes.     

Triggering of earthquakes at Koyna,India and hammer drilling for the pilot borehole

Natural Hazards - Koyna located near the West Coast of India is an outstanding case of artificial water reservoir-triggered seismicity. It is observed that annually earthquakes get triggered in the...     

Lithostratigraphic contact – a significant site for hydrogeological investigation in crystalline fractured-rock terrains

Estimating the hydrogeologic control of fractured aquifers in hard crystalline and metamorphosed rocks is challenging due to complexity in the development of secondary porosity. The present study in the Precambrian metamorphic terrain in and around the Balarampur of Purulia district, West Bengal, India, aims to estimate the hydrogeologic significance of lithostratigraphic contacts using fracture characteristics obtained from surface bedrock exposures supported by hydrological data from the existing dugwells. This study involves the domain-wise analysis of the frequencies of fractures that control the fracture-porosity. The domain-wise study reveals higher fracture-frequencies adjacent to the lithostratigraphic contacts. The concurrence of lithostratigraphic contacts with the occurrences of high-discharging wells and also with the deep weathered zone in low-lying areas is clearly established, thus assigning the lithostratigraphic contact as hydrogeologically significant. An increase in frequencies of the fractures within the ‘influence zone’ of the lithocontact, is clearly visible. Among those fractures, particularly, which make the angle greater than the ‘limiting angle’ with the lithocontact are characterised by increased frequencies. However, brittle rocks like quartz biotite granite gneisses, phyllite and epidiorite show high porosity of fracture, within the ‘influence zone’ of the lithostratigraphic contact. Enhanced deepening of the weathered-zone at lower topographic region may perhaps be a plausible explanation for this increased fracture-porosity at lithocontact to assign it as a hydrogeologically significant transmissive zone within fractured rocks.     

Geological introduction to strontium-rich sub-soil brine with emphasis on the Little Rann of Kutch and Bhavnagar,Gujarat

The methodology for green mining operation, one that extracts minerals from waste brine water for eco-friendly products, is appealing. Little Rann of Kutch (LRK) and the sites near Bhavnagar associated with producing sub soil brine water which contain strontium up to 215 mg/L. This value is significant considering its value in sea water (~8 mg/L). The high-strontium brines also contain elevated lithium (up to 2.98 mg/L) and uranium (up to 0.1 mg/L). The occurrence of strontium in the India’s brine water is poorly understood and inadequately represented in the literature. The objectives of this report, therefore, are to illustrate where strontium-rich brine waters occur in Gujarat (India). The investigation of strontium, lithium and uranium in sub-soil brine was accomplished by the ICP-OES instrument. We have checked the pH, density, specific gravity and Degree Bowme (DB’) of the all samples. Alkali and alkaline earth metals like Na, K, Mg, Ca and Ba; metalloid B; transition element like Zn, Cr and Fe; heavy metals like Cd, Pb and Ni were also analysed for toxicity evaluation and anion Cl^– and SO₄ ^–2 were analysed by classical methods. Field wise, there is considerable variation in strontium, lithium and uranium in sub-soil brine water.     

Gold - sulphide mineralization in ultramafic-mafic-granite complex of Jashpur,Bastar craton,central India: Evidences from geophysical studies

Time Domain Induced Polarization (TDIP) investigation in conjunction with high resolution electrical resistivity tomography surveys carried out at seven sites along a 5.2 km line in Jashpur and Raigarh districts of Chhattisgarh State yielded promising results leading to the demarcation of mineralized zones. These sites are confined to ultramafic-mafic-felsic intrusive complexes representing gabbro-pyroxenite-granite sequences characterized by gold - sulphide mineralization. Two dimensional (2D) geophysical datasets yielded interesting results and a good correlation is found between 2D inverted resistivity tomography and time domain induced polarization (IP) models. Both high resistivity-high chargeability as well as low resistivity-high chargeability conditions have been inferred from these datasets. This observation is consistent with conductive metallic mineralization. Interpretation of the Pharsabahar-Pandripani site, reveals a chargeability magnitude of 9-14 mV/V, which represents a strong metallic conductor associated with gold-sulphide ore body. The results at Samarkachar site are equally significant, showing a good correlation with the presence of a low resistivity and high chargeability zone. Hence, the present study suggests a new scope for application of resistivity and IP tomography surveys for mineral prospecting in favourable geological settings.     

Forest biomass carbon dynamics (1980–2009) in western Himalaya in the context of REDD+ policy

Carbon emissions from forests have decreased in the past decade due to conservation efforts, however majority of carbon losses suffered in the past went unnoticed until the role of forests in mitigating climate change was realized. Forestry sector in developing countries is recognized as one of the largest and low cost mitigation options to address climate change. The present study was conducted to assess the multi-temporal biomass carbon mitigation in the temperate forests of western Himalaya using satellite (Landsat MSS, TM, ETM+) and forest inventory data. Forest type density mapping was done through on-screen visual interpretation of satellite data. After conducting preliminary survey in 2009, 45 quadrats (0.1 ha) were laid in six forest types for collecting field inventory data viz., diameter at breast height, tree height, slope and aspect. Biomass carbon (t ha^?1) was estimated for different forest types with different crown densities (open with 10–40% crown density and closed with >40%) using recommended regression equations, ratios and factors. A decreasing trend of carbon (145.13–134.87 mt) was observed over the period of time. Temporal biomass carbon dynamics was analyzed for REDD+ opportunities. The temporal variation of carbon observed was found to be more useful for claiming benefits under negative options (deforestation and forest degradation) of REDD+. The study doesn’t take actual conversions to CO₂ into account. However, the findings are useful in establishing baseline emissions through temporal carbon losses. Further, the study helps in identification of location specific socio-economic drivers of losses that can be used for appropriate mitigation interventions.     

Soil slope instability along a strategic road corridor in Meghalaya,north-eastern India

The road widening carried out along National Highway-40, a strategic road corridor of north-eastern India, to ease the traffic snarls for geopolitical developments in the region. The newly exposed in situ soil slopes along National Highway-40 are on the verge of shear instability, and slope failures occur due to heavy earth cuttings. As a consequence, the road corridor witnesses several geotechnical failures during rainy seasons. The blasting activities initiated and propagated the soil creeps and falls resulting road blockades. Even a small rain shower is enough to undercut and uproot trees and transport boulders and surrounding earth materials up to the corridor. Besides, landslides are also prone to damage demographic areas and settling house units, thus invites for preventive measures towards hill slope management as these slopes make the highway corridor unsafe to the commuters. Therefore, the present study is aimed to investigate the stability of the hill cut soil slopes and to suggest possible stabilisation measures. The study also highlighted that steep soil slopes with high moisture content are prone to landslides mainly due to infiltration, and water flows on the slopes during high and prolonged rainfall. The highly plastic soils rich in silt and clay size particles with high moisture content cause soil/debris slide and flow. The numerical modelling of slopes using Fast Lagrangian Analysis of Continua (FLAC) codes (version 4.0) indicates failures in excavated high angle cut slopes. The re-excavation and benching of unstable slopes with geonets or bionets or jute matting to promote vegetation growth were suggested as stabilisation measures by field investigation, laboratory studies and numerical analysis of slopes.     

Significance of glacio-morphological factors in glacier retreat: a case study of part of Chenab basin,Himalaya

A study has been carried out in part of Chenab basin,Himalaya to understand the relationship between glacio-morphological factors and change in glacial area. Initially change in areal extent of glaciers was derived for two time frames(1962-2001/02 and 2001/02-2010/11). The study comprised of 324 glaciers for the monitoring period of 1962-2001/02 for,which 11% loss in glacial area was observed. Two hundred and thirty-eight glaciers were further monitored between 2001/02 and 2010/11. These glaciers showed an area loss of 1.1%. The annual deglaciation has been found to be higher during the period of 1962-2001/02 compared to 2001/02-2010/11. The spatial and temporal variability in deglaciation was also addressed usingglacio-morphic parameters. Area,length,percentage of debris cover,and various elevation parameters of glaciers were observed to have significant controls on relationships to the rate of glacial shrinkage. Largerarea and longer glaciers show a lower percentage of retreat than smaller and shorter ones. Moreover,glaciers located at lower altitudes and having gentle slopes show more area retreat. The results of area retreat in debris covered and debris free glaciers supports that the glaciers covered by debris retard ice melting at some extent. 158 glaciers were observed having no debris cover,and these exhibit 14% of loss in surface area. In glaciers having 40% debris cover,8% of deglaciation was observed. The glaciers located below equilibrium line altitude(ELA) have experienced 4.6% of deglaciation for the time frame 2001/02 – 2010/11 whereas it was found to be 1.1% for the glaciers occurring above ELA. However,theorientation of glaciers did not show any considerable influence on glacial change based on hypothesis.