A model of the subsidence history of the West Coast of India

The occurrence of earthquakes all along the West Coast of India and in the Arabian Sea is explained systematically in terms of the interaction between the underthrusting Indian ocean floor and the Indian subcontinent. This north ward compression due to the repeated underthrusting of the oceanic floor has caused the formation of trenches, grabens and normal faults on the continental margin.     

Geology of Ladakh,Lahaul and spiti regions of Himalaya with special reference to the stratigraphic position of flysch deposits

An attempt has been made to produce the geological map of Ladakh, Lahaul and Spiti regions of Himalaya on the basis of the field work done by the authors and the observations made by earlier workers. The stratigraphy of this region has been discussed in the light of new fossil finds from different stratigraphical horizons. Stratigraphical columns have been prepared and the formations of this region have been correlated with those exposed in other parts of the Himalaya. The age of the flysch deposits (Indus Flysch of Ladakh and Chikkim Shales of Spiti) has been defined on the basis of the microfauna.

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Zusammenfassung Aus Feldarbeiten und bereits vorliegenden Fakten resultierte eine neue geologische Karte des Gebietes von Ladakh, Lahaul und Spiti im Himalaya. Die Stratigraphie wird mit Hilfe neuer Fossilfunde geändert und mit anderen Teilgebieten des Himalayas verglichen. Das Alter der Flyschserien (Indus-Flysch von Ladakh und Chikkim-Shales von Spiti) wurde mit Hilfe von Mikrofaunen bestimmt.

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Résumé Les levés de terrain des auteurs, combinés avec des travaux antérieurs, ont permis de dresser une nouvelle carte géologique du Ladakh, Lahaul et Spiti dans l'Himalaya. La stratigraphie a été modifiée grâce à de nouvelles découvertes de fossiles et comparée avec celle d'autres régions de l'Himalaya. L'âge de la série du flysch (Flysch de l'indus de Ladakh et schistes de Chikkim de Spiti) a été déterminé à l'aide de microfaunes.

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Variations in the surface texture of suspended quartz grains in the Loire River: an SEM study

Statistical size distribution and scanning electron microscopic studies of suspended sand grains in the Loire River at Montjean, France were carried out over a period of a year (hydrological cycle) to discern seasonal variations. The sand fraction in suspension is better sorted during winter (average mean = 0.69 mm, median = 0.65–0.95 mm, sorting value, σ= 1.1–1.35) and is dominated by quartzo-feldspathic minerals. During summer, on the contrary, this fraction is rich in mica minerals and is poorly sorted (average mean = 1.21 mm, median = 0.33–0.95 mm, sorting value, σ= 1.4–2.0). The grain size of the coarser fraction shows a tendency to increase with river discharge up to an optimum discharge of about 1000 m³ s^-1 and thereafter decreases. Scanning electron photomicroscopy of quartz grains from the suspended sand population indicates that both mechanical and chemical features occur. The former (conchoidal fractures, mechanical fractures and breakage) dominate in the samples collected near the water surface during winter floods and the latter (solution pits, vermicular features, silica flowers, neogene silica and diatoms) in the samples from the bottom during low summer flows. During summer, chemical action takes place on sediments prior to or upon their deposition. Sediments that are resuspended during winter floods undergo mainly physical processes (attrition/abrasion). Mixed surface features are, therefore, observed during average and low river discharge. Inheritance of these surface features from the source area is, however, not completely excluded. Thus, the history of quartz grains in suspension can be reconstructed from SEM exoscopic studies: therefore, it can be proposed that the fluvial quartz grain surface textures result from a combination of alternating chemical and physical processes.     

Composition and mineralogy of suspended sediment in the fluvio-estuarine zone of the Loire River, France

The fluvio-tidal transition of suspended sediment in terms of mineralogy and composition in the Loire River drainage basin, the largest French river basin, was investigated in the fluvial zone at Montjean and in the tidal zone at Mauves-Thouaré, for a complete seasonal cycle. At Montjean, where the river experiences unidirectional flow, the composition and mineralogy (especially clays and clay minerals) of river suspended material (RSM) are governed by the river discharge, upstream contributions, climatic conditions and microbiological activities. However, due to reversing tidal and river currents at Thouaré, in the zone of tidal dynamics, these relations are changed. In the downstream direction sand and clay content in the RSM decrease while the silt content increases. Among clay minerals, between these two observation stations, montmorillonite remains constant, kaolinite diminishes, and the other minerals increase downstream. Combustible material (organic) and nitrate (NO₃) contents in the RSM increase whereas the phosphate (PO₄^3-) and CaCO₃ contents decline considerably during transport. At the head of the tidal zone, where the river flow encounters the tidal influence, there is a relatively stationary water mass (tidal slack) where sands, clays, phosphate, carbonate and silica are deposited by physical and chemical processes. Physical sedimentation takes place by simple gravitational deposition (sands), and by sorting and complicated differential settling (clays); chemical sedimentation takes place by precipitation (calcite-CaCO₃; apatite-Ca₅ (PO₄)³ (OH,F,Cl); coagulation of dissolved silica-SiO₂) in connection with seasonal algal bloom and eutrophic events.     

The Uttarkashi earthquake of 20 October 1991: field observations

The epicentre of the destructive 20 October 1991 earthquake is in the north-east of the Uttarkashi region of the Higher Himalaya. The earthquake was felt up to 250–350 km away from Poh and Keylong in the north to Delhi in the south and beyond Chandigarh in the west. Seismologists of the Seismotectonic Group of Wadia Institute of Himalayan Geology studied fissures, surface breaks, and the foreshock and aftershock activity caused by this event. Land fissures show normal dislocations of 0.06–1 m, run E-W and NE-SW in the epicentral region and could be followed for 30–40 km.     

Absolute age determinations of crystalline rocks of Manali-Jaspa region,Northwestern Himalaya

Comparison of “argon” absolute age determinations of crystalline rocks of the “Crystalline Nappe” (Kumar, 1971, unpublished Ph. D. thesis) and of the “root-zone” (Jaspa granite) has led to an important conclusion concerning the interpretation of the development of the “crystalline nappe” and its rejuvenation.     

Dry/wet snow mapping based on the synergistic use of dual polarimetric SAR and multispectral data

We propose a multi-sensor multi-spectral and bi-temporal dual-polarimetric Synthetic Aperture Radar(SAR) data integration scheme for dry/wet snow mapping using Sentinel-2 and Sentinel-1 data which are freely available to the research community. The integration is carried out by incorporating the information retrieved from ratio images of the conventional method for wet snow mapping and the multispectral data in two different frameworks. Firstly, a simple differencing scheme is employed for dry/wet snow mapping, where the snow cover area is derived using the Normalized Differenced Snow Index(NDSI). In the second framework, the ratio images are stacked with the multispectral bands and this stack is used for supervised and unsupervised classification using support vector machines for dry/wet snow mapping. We also investigate the potential of a state of the art backscatter model for the identification of dry/wet snow using Sentinel-1 data. The results are validated using a reference map derived from RADARSAT-2 full polarimetric SAR data. A good agreement was observed between the results and the reference data with an overall accuracy greater than 0.78 for the different blending techniques examined. For all the proposed frameworks, the wet snow was better identified. The coefficient of determination between the snow wetness derived from the backscatter model and the reference based on RADARSAT-2 data was observed to be 0.58 with a significantly higher root mean square error of 1.03 % by volume.     

Qualitative and quantitative assessment of TanDEM-X DEM over western Himalayan glaciated terrain

Glaciers have a high impact in the socio-economic sectors including water supply, energy production, flood and avalanches. A high precision digital elevation model (DEM) is required to monitor glaciers and to study various glacier processes. The present study deals with the qualitative and quantitative evaluation of the DEM generated from the bistatic TanDEM-X data by comparing it with GPS, Ice, Cloud, and land Elevation Satellite (ICESat) data and standard global DEMs such as Shuttle Radar Topography Mission (SRTM) and Advanced Space-borne Thermal Emission and Reflection Radiometer Global DEM (ASTER GDEM). The study area consists of highly undulating glaciated terrain in western Himalaya, India. The results reveal that TanDEM-X is slightly better than SRTM both qualitatively and quantitatively, whereas ASTER GDEM showing maximum discrepancy among the three DEMs. The Root Mean Square Error (RMSE) of the TanDEM-X DEM with respect to GPS is 3.5 m at lower relief and 11.9 m at glaciated terrain, against 6.7 and 12.5 m for SRTM and 9.3 and 19.8 m for ASTER GDEM, respectively, for the same sites. On an average, for the whole study area, the RMSE of TanDEM-X is 7.9 m, SRTM is 9.3 m and ASTER GDM is 14.2 m. The RMSE of TanDEM-X, SRTM and ASTER GDEM with respect to ICESat are 16.3, 19.9 and 101.1 m, respectively. It is evident from the analysis that though SRTM is closer to TanDEM-X in terms of accuracy in the mountainous terrain, however, TanDEM-X will be more useful for studying glacier dynamics and topography.     

Tectonics and earthquake mechanism of the shallow earthquake seismic belt,the Himalaya

The foci distribution of upper mantle earthquakes occurred between 1961 and 1972 in Himalayan, Tibetan and Hindukush regions, were studied and compared. The V-shaped pockets above a vertical plane have shown a relationship with the dip-slip type or normal faulting at the borders of the continental plates. The left-lateral and right-lateral displacements of Kirthar-Sulaiman shear zone and Brailly fault respectively found by the focal mechanism indicate a relative difference in motion between the Kashmir region and Nepal region and the uniform and right angle displacement of Tibetan Plateau has produced the Saradah depression. On the basis of seismic and geological evidences a simple tectonic model is proposed.     

Mineral growth and deformation in the crystalline schist of Central Himalaya,around Rohtang Pass (H.P.), India

Detailed mesoscopic and microscopic textural relationship lead to conclude that the size, shape and orientation of biotite porphyroblasts were predominently controlled by the temperature at which metamorphism occurred with respect to kinemetic and dynamic factors of deformation.