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211.
P. P. Chakraborty A. Sarkar S. K. Bhattacharya P. Sanyal 《Journal of Earth System Science》2002,111(4):379-390
Enriched13C/12C ratios with δ13C ∼3%0 (w.r.t PDB) of two Late Riphean (∼ 700-610 Ma) intracratonic carbonate successions viz., Bhander Limestone of Vindhyan
Basin and Raipur Limestone of Chattisgarh Basin suggest higher organic productivity during this period. This view is supported
by sedimentological evidence of higher biohermal growth and consequent increase in depositional relief in the low gradient
ramp settings inferred for these basins. Oxygen isotope analysis of these carbonates show distinct segregation between enriched
deeper water carbonate mudstone and depleted shallow water stromatolite facies that received fresh water influx. This shows
that facies-specific analyses can be useful in understanding the depositional setting of these sediments. 相似文献
212.
Kaustubha Bhattacharya 《Journal of Earth System Science》1993,102(1):113-120
Time series of proxy data representing long-term variation of the terrestrial climate presumably show aperiodic changes, which
has given rise to the hypothesis that the dynamics of the earth’s climate is governed by a strange attractor. Here a study
of such attractors is presented, with emphasis on determination of its dimension and the reported results. Finally, a one
dimensional delayed albedo feedback climate model is discussed with the related strange attractor and its dimension. 相似文献
213.
Seven pockets of variable dimensions of strata-bound sparry magnesite within the Middle Proterozoic Gangolihat Formation around Bauri in the Almora district, Kumaun, Lesser Himalaya, have been investigated petrographically and geochemically. The lenses and pockets of megacrystalline, bladed, occasionally stellate, magnesite aggregates invariably enclosed by stromatolitic or massive dolostones, often exhibit a concordant relationship with the latter. Besides the sharp contrast in crystal-linity of magnesite and dolostones and the patches of the latter in the former, relict features such as layers of chert, cryptocrystalline silica veins and stromatolitic structures are discernible in the magnesite. There is a gradual increase in MgO and FeO with a corresponding decrease in CaO, and a striking depletion in Sr from dolostone to magnesite but no noteworthy variation in other major or minor elements nor in insoluble contents. Both the dolostones and magnesites are characterised by the same range of oxygen isotope ratios. However, a marked enrichment of lighter carbon isotopes in magnesites is noted. Based on these observations, it is inferred that the magnesite around Bauri is a product of diagenetic magnesitisation of penecontemporaneous dolomite in a restricted biohermal tidal flat environment. 相似文献
214.
Jayanta Bhattacharya 《Pure and Applied Geophysics》1969,73(1):93-98
Summary The propagation of a certain type of surface waves in a non-homogeneous elastic layer of finite thickness lying in welded contact with a semi-infinite homogeneous elastic medium has been investigated in this paper. The surface wave is characterised by the fact that the dilatation and the vertical displacement component are both zero. It has been proved that such disturbance can propagate only when the phase velocity of the wave is greater than the shear wave velocity and the group velocity is inversely proportional to the phase velocity. 相似文献
215.
S. N. Bhattacharya 《Pure and Applied Geophysics》1967,67(1):33-42
Summary The displacements on the free surface of a homogeneous isotropic semi-infinite medium has been obtained assuming a moving normal stress on the surface. It has been studied how the displacements behave with (1) the direction of propagation of the source with respect to the recording station and (2) the velocity of the source. 相似文献
216.
Intimate association of 2 billion years old stromatolite with pyritic lead-zinc ores in the Precambrian polymetallic deposit at Rajpura-Dariba in Rajasthan, which hitherto remained unreported, provides an additional documentation of the syn(-dia)-genetic mineralization. The growth form and petrography of the stromatolite structure have been described and an explanation sought regarding the concentration of sulfides along the siliceous and carbonaceous laminations, as well as in the intercolumnar regions. Consideration of the geologic features noted in the mineralized zone and surrounding region suggests that the stratiform ores were deposited in a near-shore shallow marine environment, developed on basement highs and associated with euxinic conditions. Later, the ores were metamorphosed under conditions reaching upto amphibolite facies during a three-stage deformational history of their enclosing rocks. Some salient features of the secondary structures in the ores have been discussed in relation to this deformation history. 相似文献
217.
S. N. Bhattacharya 《Pure and Applied Geophysics》1976,114(6):1021-1029
Love wave dispersion in various semi-infinite media consisting of inhomogeneous layers is discussed. The phase and group velocities are computed when shear wave velocity and density in each inhomogeneous layer are varying exponentially with depth. At the beginning one or two inhomogeneous layers over a homogeneous semi-infinite medium are considered. The dispersion results for these structures are compared with those for their approximations with homogeneous layers. Comparisons show that differences of phase and group velocities for the original models from those for their approximated models (i) increase with the increase of wave number and (ii) are larger for group velocity than for phase velocity. The difference is approximately proportional to the rate of change of parameters in the layers. Finally, dispersion curves are obtained for model IP3MC, which consists of many inhomogeneous and homogeneous layers over a homogeneous semi-infinite medium. The results are compared with the observed group velocity data across the Indian Peninsula. 相似文献
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