Evaluation of metal contamination in coastal sediments of the Bay of Bengal, India: geochemical and statistical approaches

Surface sediment samples collected from the inner shelf region of the Bay of Bengal, were analysed for the major elements and total and acetic acid available trace elements (Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Si, Zn) to evaluate geochemical processes influencing their distribution. Major elemental analysis showed that the sediments had high concentrations of Si and relatively low concentrations of Al and Fe. Both major elemental and trace metal concentrations indicated that the sediments represent weathered products of granite and charnockite. Normalization of metals to Al indicated relatively high enrichment factors for Pb, Cd, Zn and Cr. The higher proportions of nondetrital Pb (66%), Cd (41%) and Co (28%) reveal metal contamination due to anthropogenic inputs. Factor analysis (FA) identified six possible types of sedimentological and geochemical associations. The dominant factor accounting for 26.9% of the total variance identifies an anthropogenic input and accumulation of nondetrital Cd, Co, Cr, Ni and Pb. Association of these metals with CaCO3 reveals that shell fragments in the surface sediments are likely act as a carrier phase for nondetrital metals. The results are discussed in the context of the sources and pathways of elements in the Bay of Bengal.     

Equilibrium structures of rotationally and tidally distorted stellar models

In this paper we present a method for computint the equilibrium structures of rotationally distorted stars as well as rotationally and tidally distorted primary components of the stars in binary systems. The method is based on the averaging technique of Kippenhahn and Thomas (1970) and utilizes the concepts of Roche equipotentials (Kopal, 1972). The method takes into account terms up to second-order of smallness in the rotational and tidal distortion parameters. The use of the method in obtaining the equilibrium structures of certain rotationally and (or) tidally distorted models of Main-Sequence stars is also illustrated.     

Effects of partial frequency redistribution on the level population densities in a resonance line

We have obtained a simultaneous solution of the statistical equilibrium equation for a non-LTE two-level atom and the radiative transfer equation in the comoving frames by employing the angle-averaged partial frequency redistribution.R _i with isotropic scattering. In the first iteration we have set the population density of the upper level equal to zero and allow it to be populated in the subsequent iterations. The solution converges within two to four iterations. The process of iteration is terminated when the ratios of population densities in two successive iterations at each radial point, attain an accuracy of 1%. The effects of partial frequency redistribution is to increase the population density of the upper level. Radial gas motions do not seem to have significant effects, although in highly extend geometries, velocity gradients change the population densities considerably.     

Assessment of the groundwater potential and quality in Bhatsa and Kalu river basins of Thane district, western Deccan Volcanic Province of India

Scarcity of groundwater necessitates the present study to evaluate groundwater potential and quality for designing suitable water management plans in the Bhatsa and Kalu river basins in the Thane district in the western Deccan volcanic province of India. A Geographical Information System platform is used to integrate and spatially analyse multiparametric data comprised of satellite, topographical, geological and hydrogeological information to generate several thematic maps, including groundwater potential zonation map. This study reveals that 70% of the area has medium to low groundwater potential, while only 10% has high potential. The static and dynamic groundwater potentials are estimated to be 10.7 and 4.8% of the annual rainfall. The groundwater quality in terms of hardness, total dissolved solids, salinity and chloride is suitable for domestic and irrigational purposes. A database is developed for sustainable water management program for the region and areas where suitable water conservation techniques need to be adopted are identified.     

Surface heat flow and probable evolution of Deccan volcanism

In the light of surface heat-flow observations, as well as other related geological and geophysical data, the origin of the Deccan basalts has been examined. The Indian lithosphere, after its detachment from Gondwanaland, apparently traversed a rising plume at La Réunion, which virtually bored through the lithosphere to emerge as the Deccan Trap volcanism on the surface. Subsequent volcanic and plutonic activity appears to have continued not only up to the Oligocene, as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features — the West Coast faults, the Narmada-Son-Tapti lineament, and the Cambay Graben — but also up to the Mio-Pliocene, as indicated by the heat flow and gravity data over the Cambay Graben. The dyke-swarms and sills, which are mostly post-trappean, evolved from the lithosphere after the Indian Plate moved away from the hot spot.     

Auxiliary functions of the Hilbert transform in the study of gravity anomalies

The auxiliary functions, namely amplitude, phase, envelope and instantaneous frequency of Hilbert transform over gravity anomalies of 2-D sphere, vertical fault block and horizontal circular cylinder are studied. The characteristics of these functions are established in locating and identifying the sources. The method is illustrated with a theoretical example in each case and supported by field data of gravity anomaly over Humble dome and spherical model of the Satak-Mansar area, Nagpur District, India.     

Analysis of gravity gradients over a thin infinite sheet

A simple method to interpret gravity gradients over a thin infinite dipping sheet is discussed. The Hilbert transform is used to compute the vertical gradient from the horizontal gradient of the gravity field. The method is illustrated with a theoretical example.     

Interpretation of gravity and magnetic anomalies caused due to spherical bodies

Summary The method of continuation has been used to obtain the master curves for gravity and magnetic anomalies caused by spherical bodies. The procedure to calculate the depth of burial and radius of spherical bodies has been outlined.