Landslide hazard zonation mapping and comparative analysis of hazard zonation maps     

S. Sarkar  R. Anbalagan 《山地科学学报》2008,5(3):232-240

Landslide hazard zonation mapping at regional level of a large area provides a broad trend of landslide potential zones. A macro level landslide hazard zonation for a small area may provide a better insight into the landslide hazards. The main objective of the present work was to carry out macro landslide hazard zonation mapping on 1：50,000 scale in an area where regional level zonation mapping was conducted earlier. In the previous work the regional landslide hazard zonation maps of Srinagar- Rudraprayag area of Garhwal Himalaya in the state of Uttarakhand were prepared using subjective and objective approaches. In the present work the landslide hazard zonation mapping at macro level was carried out in a small area using a Landslide Hazard Evaluation Factor rating scheme. The hazard zonation map produced by using this technique classifies the area into relative hazard classes in which the high hazard zones well correspond with high frequency of landslides. The results of this map when compared with the regional zonation maps prepared earlier show that application of the present technique identified more details of the hazard zones, which are broadly shown in the earlier zonation maps.  相似文献   

High-resolution profile of stable isotopes and iridium across a K/T boundary section from Koshak Hill, Mangyshlak, Kazakhstan     

A. Sarkar  S.K. Bhattacharya  P.N. Shukla  N. Bhandari  D.P. Naidin 《地学学报》1992,4(5):585-590

Oxygen and carbon isotopes were measured to a high depth resolution in a nannoplankton carbonate sequence spanning the Cretaceous-Tertiary boundary at Koshak Hill, Mangyshlak Peninsula, Kazakhstan. The boundary is characterized by the presence of a ∼ 1 cm thick clay layer having a sharp peak in iridium concentration with a maximum value of 3.7 ng g^-1. The δ¹⁸O data reveal rapid (∼10³ years) excursion of sea-surface temperature at the boundary where an initial cold pulse is followed by a persistent warm period. The δ¹³C data, in contrast, indicate only a gradual change in productivity across the boundary. The observations suggest a biogeochemical scenario for the boundary event pertaining to shallow epicontinental seas.  相似文献   

    

S. C. Sarkar  S. Kabiraj  S. Bhattacharya  A. B. Pal 《Mineralium Deposita》1997,32(6):622

  相似文献   

Alteration of volcanic glass to well-crystallized ferrosaponite in the vesicles of the Deccan trap basalts at Bhuleshwar Ghat section,Pune district,Maharashtra     

Pradeep K. Sarkar  Devdutt V. Upasani  Vibhuti Wani 《Journal of the Geological Society of India》2016,88(1):22-28

Clay minerals formed mainly by the alteration of volcanic glass are reported by many workers. The commonly formed minerals belonging to the smectite group especially nontronite and ferrosaponite are widely reported by many in basalts. However, most of the reports suggest the formation of ferrosaponite in marine conditions (Zhou et al., 1992; Chen et al., 1996) or by hydrothermal solutions (Shayan et. al., (1988)). Origin of ferrosaponite in continental flood basalts by a mechanism of alteration of volcanic glass to ferrosaponite is reported in the paper. The different stages involved in the alteration process are also highlighted.  相似文献   

Early Eocene calcareous algae and benthic foraminifera from Meghalaya,NE India: A new record of microfacies and palaeoenvironment     

Suman Sarkar 《Journal of the Geological Society of India》2016,88(3):281-294

Early Eocene carbonate sediments of the Umlatdoh Limestone (Meghalaya, N-E India) represent a shallow marine shelf environment. The major biotic components characterizing these carbonates are calcareous green algae and small to larger benthic foraminifera. Based on the biogenic associations and general sedimentological features, five major facies types (MFTs) are distinguished. They are dominated by poor to moderately sorted grainstones followed by packstones, rudstones and wackestones. Considerable abundance of Halimeda, scarcity of z-corals and poor to moderate occurrence of filter-feeding organisms imply mesotrophic to a slightly oligotrophic nutrient regime. Rare occurrence of geniculate coralline algae is probably due to the lack of suitable substrate and environmental conditions. High incidence of grainstones and packstones, fairly preserved microfossils and few reworked specimens indicate a parautochthonous mode of deposition. Preponderance of Alveolina and Nummulites indicate the possible advent of larger foraminiferal turnover (LFT) in the east Tethys during or even before early Eocene. A conceptual palaeoenvironmental model for the studied succession is provided to showcase various facies gradients, bathymetry levels and shelf zones pertinent to the Umlatdoh Limestone.  相似文献   

Climate‐modulated sequence development in a tropical rift basin during the Late Palaeocene to Early Eocene super greenhouse Earth          下载免费PDF全文

Arpita Samanta  Melinda K. Bera  Anindya Sarkar 《Sedimentology》2016,63(4):917-939

Sequence developments in rift basins are considered to be influenced largely by tectonics and to a lesser extent by eustatic sea‐level and climate. Studies indicate that in passive margin basins, climate can mask the effects of tectonics and eustasy by modulating the sediment supply. It is, however, less understood how the sedimentary sequence in rift basins might respond to strong climatic fluctuations where tectonic pulses generate rapid accommodation space. Here a case study has been provided to assess the effect of climate vis à vis sea‐level and tectonics on sequence development in the Cambay rift basin, western India, during the Early Palaeogene (Late Palaeocene to Early Eocene) super greenhouse globe. Facies analysis of this shale–lignite sequence suggests deposition in a lagoon/bay, developed over the Deccan Trap basement. Detailed sequence stratigraphic analysis using basin‐wide representative composite sections, marker lignite seam, event bed and high‐resolution carbon isotope (δ¹³C) chemostratigraphy suggest an overall transgressive motif. Among the three prominent Early Eocene eustatic highstands, only the one at ca 53·7 Ma is expressed by the thickest coal accumulation throughout the basin. Expression of the other sequence stratigraphic surfaces is subdued and can be due to the overall finer grain size of the sediment or local variation in the subsidence rate at different fault‐controlled mini‐basins. Enigmatic presence of a maximum flooding surface coinciding with the 53·7 Ma climate event (Eocene Thermal Maximum 2), manifested by negative carbon isotope excursion, indicates possible influence of climate over and above tectonics in developing the rift sequence. Qualitative rainfall variation assessed using the magnitude of the carbon isotope excursion and pollen abundance show that a relatively dry/low precipitation climatic phase during the Eocene Thermal Maximum 2 hindered the siliclastic supply to the basin. Thus, it has been inferred that climate‐induced high siliciclastic supply possibly enhanced the autocyclic reorganization and hindered the development of the key sequence stratigraphic surfaces across the basin during climate extremes.  相似文献   

Characterization of tidally influenced seasonal nutrient flux to the Bay of Bengal and its implications on the coastal ecosystem          下载免费PDF全文

Palash Debnath  Abhijit Mukherjee  Kousik Das 《水文研究》2018,32(9):1282-1300

Submarine groundwater discharge (SGD) introduces solute and nutrients to the global oceans, resulting in considerable nutrient cycling and dynamics in the coastal areas. We have conducted high‐resolution, spatio‐temporal, lunar tidal cycle patterns and variability of discharged solute/nutrient assessment to get an overview of seasonal nutrient flux to the Bay of Bengal in eastern parts of the Indian subcontinent. Whereas the premonsoon season SGD was found to be dominant in the marine influence (M‐SGD), the postmonsoon season was found to be predominated by the terrestrial component of SGD (T‐SGD), extending from coast to near offshore. The solute fluxes and redox transformation were found to be extensively influenced by tidal and diurnal cycles, overlapping on seasonal patterns. We have assessed the possible role of SGD‐associated solute/nutrient fluxes and their discharge mechanisms, and their associated temporal distributions have severe implications on the biological productivity of the Bay of Bengal. The estimated annual solute fluxes, using the average end‐member concentration of the SGD‐associated nutrients, were found to be 240 and 224 mM·m^?2·day^?1 for NO₃^? and Fe_tot, respectively. Together with huge freshwater flux from the Himalayan and Peninsular Indian rivers, the SGD has considerable influence on the bay water circulation, stratification, and solute cycling. Thus, the observation from this study implies that SGD‐associated nutrient flux to the Bay of Bengal may function as a nutrient sink, which might influence the long‐term solute/nutrient flux along the eastern coast of India.  相似文献   

Can an annual flood induce changes in channel geomorphology?     

Islam  Aznarul  Sarkar  Biplab  Saha  Ujwal Deep  Islam  Mainul  Ghosh  Susmita 《Natural Hazards》2022,111(1):1019-1046

The present study has been a pioneering effort examining the role of an annual flood as a potent stimulus inducing changes in channel geomorphology of the Mayurakshi River, India. Twenty cross sections have been considered for the measurement of various hydro-geomorphic attributes of the river in both the pre- and post-flood conditions in 2018. The study sensed an escalating trend for channel width, width/depth ratio, and wetted perimeter while the reverse was also detected for average depth, maximum depth, cross-sectional area, and hydraulic radius. For example, the width/depth ratio recorded an increase of?~?11%, and the hydraulic radius depicted a decrease of?~?8%. Furthermore, channel asymmetry, bed asymmetry and bed relief index experienced a decrease after the flood. The sudden hydraulic impulse during monsoon flood as manifested in velocity, discharge, specific stream power, Reynolds number, Froude number increases the erosivity of the fluid. Besides the hydraulic factors, bank material (massive sandbank susceptible to hydraulic action and mixed bank constituted by alternate bands of sand and silt, and vulnerable to failure by piping action) brings substantial changes in channel morphology. Moreover, anthropogenic interventions such as sand mining are found to play a significant role in channel behaviour. The role of the multiple factors driving the morphological changes of the cross sections has been unpacked using canonical component analysis.

  相似文献   

Analyzing Animal Movement Characteristics From Location Data   总被引：1，自引：0，他引：1       下载免费PDF全文

Dipto Sarkar  Colin A. Chapman  Larry Griffin  Raja Sengupta 《Transactions in GIS》2015,19(4):516-534

When individuals of a species utilize an environment, they generate movement patterns at a variety of spatial and temporal scales. Field observations coupled with location technologies (e.g. GPS tags) enable the capture of detailed spatio‐temporal data regarding these movement patterns. These patterns contain information about species‐specific preferences regarding individual decision‐making, locational choices and the characteristics of the habitat in which the animal resides. Spatial Data Mining approaches can be used to extract repeated spatio‐temporal patterns and additional habitat preferences hidden within large spatially explicit movement datasets. We describe a method to determine the periodicity and directionality in movement exhibited by a migratory bird species. Results using a High Arctic‐nesting Svalbard Barnacle Goose movement data yielded undetected patterns that were secondarily corroborated with expert field knowledge. Individual revisits by the geese to specific locations in the breeding and wintering grounds of Svalbard, Norway and Solway, Scotland, occurred with a periodicity of 334 days . Further, the orientation of this movement was detected to be mostly north‐south. During long‐range migration the geese use the north‐south oriented Norwegian islands as “stepping stones”, Short‐range movement between mudbank roosts to feeding fields in Solway also retained a north‐south orientation.  相似文献   

Concentration of polybrominated diphenyl ethers (PBDEs) in sediment cores of Sundarban mangrove wetland, northeastern part of Bay of Bengal (India)   总被引：4，自引：0，他引：4  

Binelli A  Sarkar SK  Chatterjee M  Riva C  Parolini M  Bhattacharya BD  Bhattacharya AK  Satpathy KK 《Marine pollution bulletin》2007,54(8):1220-1229

The paper presents the first comprehensive survey of congener profiles (12 congeners) of polybrominated diphenyl ethers (PBDEs) in core sediment samples (<63 microm) covering seven sites in Sundarban mangrove wetland (India). Gas-chromatographic analyses were carried out in GC-Ms/Ms for tri- to hepta- brominated congeners. Results pointed out a non-homogenous contamination of the wetland with summation operator(12) PBDE values ranging from 0.08 to 29.03 ngg(-1), reflecting moderate to low contamination closely in conformity to other Asian aquatic environments. The general order of decreasing congener contribution to the total load was: BDE 47>99>100>154, similar to the distribution pattern worldwide. Although tetrabromodiphenyl ether BDE 47 was found in all samples followed by hexabromodiphenyl ether BDE-154, they were not necessarily the dominant congeners. No uniform temporal trend on PBDE levels was recorded probably due to particular hydrological characteristics of the wetland and/on non-homologous inputs from point sources (untreated municipal wastewater and local industries, electronic wastes from the dump sites, etc.) of these compounds. Because of the propensity of PBDEs to accumulate in various compartments of wildlife and human food webs, evaluation of biological tissues should be undertaken as a high priority.  相似文献