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101.
Borehole direct current (dc) resistivity problems are solved using finite difference method (FDM) primarily to extend the log interpretation in the two-dimensional (2D) domain. Transitional invaded zone, flushed zone, uncontaminated zone, shoulder beds and borehole filled with mud are simulated simultaneously in the model. Linear variation of resistivity is assumed for transitional invaded zone. Normal, lateral and modified laterolog7 (LL74) electrode configuration (discussed in the text) responses were computed using expanding rectangular grid system. LL74 responses with variable geometric factor did show some superiority over the conventional normal and lateral for conductive target beds sandwiched between the resistive beds. For relatively small borehole diameter, all three probes can detect resistive target bed satisfactorily. However, for highly conductive mud both LL74 and normal electrode configuration fail to detect any signal from the target bed. Bypassing effect of the current for LL74 is more than that in normal log. Lateral log shows a signal of conductive invaded zone generated by the conductive mud. Bucking current ratio peaks and the geometric factor peaks in LL74 can detect the bed boundaries. 相似文献
102.
103.
The 4th IPCC report highlights the increased vulnerability of the coastal areas from floods due to sea-level rise (SLR).
The existing coastal flood control structures in Bangladesh are not adequate to adapt these changes and new measures are urgently
necessary. It is important to determine the impacts of SLR on flooding to analyse the performance of the existing structures
and corresponding impact to plan for suitable adaptation and mitigation measures to reduce the impacts of floods on coastal
zone. The study aims to develop a comprehensive understanding of the possible effects of SLR on floods in the coastal zone
of Bangladesh. A hydrodynamic model, which is a combination of surface and river parts, was utilized for flood simulation.
The tool was applied under a range of future scenarios, and results indicate both spatial variability of risk and changes
in flood characteristics between now and under SLR. Estimated impact on population, infrastructure and transportation is also
exposed. These types of impact estimation would be of value to flood plain management authorities to minimize the socio-economic
impact. 相似文献
104.
Runcie P. Mathews Suryakant M. Tripathi Santanu Banerjee Suryendu Dutta 《Journal of the Geological Society of India》2013,82(3):236-248
Extensive Cenozoic lignite-bearing sediments in the western part of Kutch, western India provide a unique opportunity to study the floral diversity at a crucial time of early Eocene Climatic Optimum (EECO). Rock samples representing a lignite-bearing sequence from the open cast mine at Matanomadh, Gujarat, western India were collected to study the palynofloral composition and to interpret the palaeoclimate and environment of deposition. The sequence mainly composed of lignites, shales and calcareous mudstones yielded rich assemblage consists of pteridophytic spores (7 genera, 10 species), angiosperm pollens (20 genera, 26 species), fungal remains (14 genera, 16 species) and dinoflagellate cysts. The palynofloral assemblage is marked with dominance of angiospermic pollen, particularly those having affinity with the family Arecaceae. Occurrence of fungal remains in high abundance is also noticed. Based on palynomorph contents, the studied sequence is divisible into two palynozones. It is inferred that lower part of the sequences was deposited in a near-shore environment with intermittent marine incursions whereas the depositional regime of upper part was shallow marine. The climate is found to be tropical-subtropical, humid with heavy precipitation during the deposition of Matanomadh lignite-bearing sequence. 相似文献
105.
Suryendu Dutta Michael Steiner Santanu Banerjee Bernd-Dietrich Erdtmann Silambuchelvan Jeevankumar Ulrich Mann 《Journal of Earth System Science》2006,115(1):99-112
Chuaria circularis (Walcott 1899) from the Suket Shale of the Vindhyan Supergroup (central India) has been reinvestigated for its morphology
and chemical composition using biostatistics, electron microscopy and pyrolysis-gas chromatography. Morphology and microscopic
investigations provide little clues on the specific biological affinity ofChuaria as numerous preservational artifacts seem to be incorporated. On the contrary, the predominance of η aliphatic pyrolysates
of presently studiedChuaria from India rather supports an algal affinity. Moreover, the reflectance ofC circularis can be used to obtain a comparative maturity parameter of the Precambrian sediments. The review of the age and geographical
distribution ofC circularis constrains that this species cannot be considered as an index fossil for the Proterozoic time. 相似文献
106.
107.
Subash Chandra V. A. Rao N. S. Krishnamurthy S. Dutta Shakeel Ahmed 《Hydrogeology Journal》2006,14(6):1042-1051
An integrated study was carried out to investigate the subsurface geological conditions in a hard rock environment, with the aim of identifying zones with groundwater resource potential. The study, in Bairasagara watershed, Karnataka, India, considered geomorphology, water level, resistivity imaging, self potential, total magnetic field and susceptibility. The signatures due to lineaments have been clearly identified and their role in groundwater movement has been documented. Synthetic simulation methods were used to model the electrical response of the lineament using finite differential modeling scheme. The inverted image of the field data is compared with the synthetic image and iteration were performed on the initial model until a best match was obtained resulting on the generation of the calibrated resistivity image of the subsurface. Resistivity imaging revealed that the dykes are weathered/fractured to a depth of 6–8 m and are compact at deeper levels, and that they behave as barriers to groundwater movement, yet facilitate a good groundwater potential zone on the upgradient side. The results of magnetic surveys were utilized in differentiating granites and dolerite dykes with an insignificant resistivity contrast. Geomorphological expression alone cannot reveal the groundwater potential associated with a lineament. However, characterizing the nature of the feature at depth with integrated geophysical methods provides essential information for assessing that potential.The online version of the original article can be found at 相似文献
108.
109.
P. C. Bandopadhyay Utpal Chakrabarti Abhinaba Roy 《Journal of the Geological Society of India》2009,73(2):261-267
The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep
marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded
three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia.
Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution
of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated
muddy bottom with a low rate of sedimentation is envisaged.
An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia. 相似文献
110.
Sutapa Chaudhuri Debashree Dutta Sayantika Goswami Anirban Middey 《Natural Hazards》2013,65(1):97-113
The coastal regions of India are profoundly affected by tropical cyclones during both pre- and post-monsoon seasons with enormous loss of life and property leading to natural disasters. The endeavour of the present study is to forecast the intensity of the tropical cyclones that prevail over Arabian Sea and Bay of Bengal of North Indian Ocean (NIO). A multilayer perceptron (MLP) model is developed for the purpose and compared the forecast through MLP model with other neural network and statistical models to assess the forecast skill and performances of MLP model. The central pressure, maximum sustained surface wind speed, pressure drop, total ozone column and sea surface temperature are taken to form the input matrix of the models. The target output is the intensity of the tropical cyclones as per the T??number. The result of the study reveals that the forecast error with MLP model is minimum (4.70?%) whereas the forecast error with radial basis function network (RBFN) is observed to be 14.62?%. The prediction with statistical multiple linear regression and ordinary linear regression are observed to be 9.15 and 9.8?%, respectively. The models provide the forecast beyond 72?h taking care of the change in intensity at every 3-h interval. The performance of MLP model is tested for severe and very severe cyclonic storms like Mala (2006), Sidr (2007), Nargis (2008), Aila (2009), Laila (2010) and Phet (2010). The forecast errors with MLP model for the said cyclones are also observed to be considerably less. Thus, MLP model in forecasting the intensity of tropical cyclones over NIOs may thus be considered to be an alternative of the conventional operational forecast models. 相似文献