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51.
Santanu Banerjee 《International Journal of Earth Sciences》2012,101(5):1343-1343
52.
Middle Eocene Fulra Limestone and Oligocene Maniyara Fort Formation represent platform carbonate deposits of Kutch at the north-western margin of India. These carbonates contain larger benthic foraminifera, including Alveolina, Assilina, Discocyclina, Lepidocyclina, Miogypsina, Nummulites and Spiroclypeus. This study presents paleodepositional and paleobathymetric interpretations for both formations using benthic foraminifera in combination with lithological association, sedimentary structures and early diagenetic features. The six carbonate facies comprising the Fulra Limestone indicate a depositional spectrum ranging from bar-lagoon to mid-ramp depositional conditions. It records several shallowing upward cycles, leading to emergence and formation of paleokarst. The four carbonate facies of the Maniyara Fort Formation represents deposition within the inner ramp setting in bar-lagoon and patch-reef environment, while intervening fine siliciclastics correspond to episodes of relative sea level fall. Nummulitic accumulations form low-relief bars within the fair weather wave base in both the formations. The depositional setting of the Paleogene carbonate in Kutch broadly resembles Eocene platformal deposits in the circum-Tethys belt. 相似文献
53.
In this paper, the propagation of Love waves in a fiber‐reinforced layered medium lying over an elastic orthotropic half‐space under initial stress has been investigated. We have obtained the velocity equations for Love wave in this media. It is observed that propagation of Love wave is influenced by reinforced parameters and initial stressed parameter. The velocity of Love wave has been computed for three different cases. Our computed equation of Love wave coincides with the standard equation of Love wave for the case of homogeneous layer and homogeneous half‐space (AEH Love, 1911). To study the effect of reinforced and initial stressed parameters, we have computed the numerical values for phase velocity and plotted in several figures. It is observed that the phase velocity decreases with the increases of reinforced parameters and initial stressed parameter. Using MATLAB software, GUI has been developed to generalize the effect of various parameters. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
54.
S. R. Das Gupta Chitta Ranjan Nayak Santanu Das Gupta 《Astrophysics and Space Science》1984,103(2):271-284
The present paper contains extensive tables of the values of theH-functionH(z,<0) and of the moments ofQ(x) (in terms of which the moments ofH(z, ) can be determined) appropriate for transfer of radiation in active amplifying media in which<0. These values have been computed correct to the 7th decimal place for values of in the range (–10–12)-(–1030) and for values of z[0,1] with the aid of a 48-point gaussian quadrature formula. 相似文献
55.
We used analogue modelling to investigate the factors controlling tail geometry in porphyroclast systems. Results show that: (1) σ inclusions can develop in both slipping and non-slipping modes, but δ-inclusions only form in the latter. (2) σ inclusions develop when the mantle production rate is constant and the mantle is transected by the separatrix. δ inclusions form when the mantle is initially outside the separatrix and later comes inside this line. (3) In the slipping mode, the wedge-shaped tail of σ-inclusions always has a straight external surface parallel to the shear plane, whereas in the non-slipping mode the external surface is curved inwards (external embayments). (4) Together with earlier theoretical results, σ- and δ inclusions always show stair-stepping of tails when embedded in a viscous matrix under homogeneous simple shear deformation. (5) Maximum stair-stepping occurs in the slipping mode and is at least equal to the inclusion diameter. If our models bear significant similarity to nature, then (i) the straight or curved character of σ-inclusions could mean that they had, respectively, a slipping or non-slipping interface with the surrounding recrystallized matrix, and (ii) δ-inclusions may result from shear deformation under retrogressive metamorphic conditions in thrust systems. 相似文献
56.
Pramod Kumar Pratul Kumar Saraswati Santanu Banerjee 《Journal of the Geological Society of India》2009,74(4):432-444
The Early Miocene succession of Kutch represents a mixed carbonate-siliciclastic depositional system. The carbonate part of
the succession, characterized by high abundance of shallow marine benthic fauna, hosts typical shell concentrations (also
referred as shell beds). The thickness of shell concentrations vary in scale from 5 cm to 100 cm and are separated by poorly
fossiliferous to barren silty shales/siltstones. Based on taphonomic and sedimentological observations, shell concentrations
are classified as lag, event, composite/multi-event and hiatal types. The occurrence of different types of shell concentrations
in the background of sequence stratigraphic framework is the main theme for the present study. Overall, the shell concentrations
occupy the middle part of the sequence i.e. upper part of the transgressive systems tract and lower part of the highstand
systems tract. Lag concentrations are found in the lower part of the sequence while composite concentrations, the major contributors
in the sequence, occur in upper part of the transgressive systems tract and in the lower part of the highstand systems tract.
The hiatal concentrations are associated with maximum flooding surface while the position of event concentrations is independent
of sequence stratigraphic framework. The shell concentrations occupy marine flooding surface or marine ravinement surface,
thus mark parasequence boundaries. 相似文献
57.
Saurabh Baruah Santanu Baruah Naba Kumar Gogoi Olga Erteleva Felix Aptikaev J. R. Kayal 《地震学报(英文版)》2009,(3):283-291
Strong ground motion parameters for Shillong plateau of northeastern India are examined. Empirical relations are obtained for main parameters of ground motions as a function of earthquake magnitude, fault type, source depth, velocity characterization of medium and distance. Correlation between ground motion parameters and characteristics of seismogenic zones are established. A new attenuation relation for peak ground acceleration is developed, which predicts higher expected PGA in the region. Parameters of ... 相似文献
58.
Nibir Mandal Atin Kumar Mitra Santanu Misra Chandan Chakraborty 《Journal of Earth System Science》2006,115(6):643-660
In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We
have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational
sets of dikes (NW-SE and NE-SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in
non-linear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree
of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions
from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating
fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those
of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation
and coalescence of fractures. 相似文献
59.
In the present study from the southern margin of the Central Indian Tectonic Zone, it is demonstrated how the metamorphic P–T path of ultrahigh-temperature granulite terranes can be reconstructed using the metamorphic transition in corundum granulites from early biotite melting to later FMAS solid–solid reaction. The extreme metamorphism in these rocks caused two-stage biotite melting, resulting in initial porphyroblastic garnet1 and later sapphirine–spinel1 incongruent solid mineral assemblages. During this process, the leucocratic and melanocratic layers in the corundum granulites evolved from an initial silica-oversaturated to a later silica-undersaturated domain. In the melanocratic layer, this allowed localized concentration of sapphirine-spinel1 and residual sillimanite1, producing an extremely restitic assemblage, at the culmination of peak metamorphism, BM1. BM1 is constrained at 1000 °C at relatively deep crustal levels (P 9 kbar) from the stability of ferroaugite in a co-metamorphosed Iron Formation granulite. During subsequent metamorphism (BM2), the reaction path and history in the corundum granulites shifted to the restitic domain allowing reacting sapphirine, spinel1 and sillimanite to produce coronal garnet2–corundum assemblage via a FMAS univariant reaction. In the final stages of reaction history, biotite2–sillimanite2–spinel2 assemblage was produced after garnet2–corundum due to localized melt–crystal interaction. The metamorphic sequence, when interpreted with the help of a newly constructed, qualitative KFMASH petrogenetic grid, reveals successive stages of heating, increasing pressure and cooling around the KFMASH invariant point, [Opx,Crd], which is consistent with a counterclockwise metamorphic P–T path. The near isobaric nature of post-peak cooling (ΔT 250–300 °C) is also evident from multistage pyroxene exsolution and by the appearance of lamellar and coronal garnets in the Iron Formation granulites. This study provides the first tight constraint for ultrahigh-T metamorphism along a counter clockwise P–T trajectory in the Central Indian Tectonic zone, and has important bearing for terrane correlations in this part of East Gondwanaland. In addition, the new KFMASH grid allows evaluation of metamorphic phase relations in ultrahigh-T, corundum-bearing and corundum-absent aluminous granulites. 相似文献
60.
Olga Erteleva Felix Aptikaev Saurabh Baruah Santanu Baruah Sajal K. Deb J. R. Kayal 《Natural Hazards》2014,70(1):733-753
Strong ground motion parameters for the Guwahati city area, the capital city of the state of Assam in northeast India, are examined with the help of data accrued from local as well as worldwide network. Empirical relations are proposed for the ground motion parameters as a function of earthquake magnitude, distance, fault type, source depth and velocity characteristics of medium. Seismotectonics of the study region is examined, and a maximum credible earthquake M S ~ 8.0 is presumed from the Brahmaputra fault, the nearest source zone in the city area. Such great/major event may cause intensity of the of 9.3 with a probability of 0,95 in the Guwahati city during time interval of 500 years. Further, the design spectrum with 67 % confidence level and the synthetic three-component accelerograms are constructed. These results are much relevant and useful for structural engineering to mitigate seismic hazards in the region. 相似文献