Crustal shortening in convergent orogens: Insights from global positioning system (GPS) measurements in northeast India     

Malay Mukul  Sridevi Jade  Anjan Kumar Bhattacharyya  Kuntala Bhusan 《Journal of the Geological Society of India》2010,75(1):302-312

Deformation in active mountain belts like the Himalaya is manifested over several spatial and temporal scales and collation of information across these scales is crucial to an integrated understanding of the overall deformation process in mountain belts. Computation and integration of geological shortening rates from retrodeformable balanced cross-sections and present-day convergent rates from deforming mountain belts is one way of integrating information across time-scales. The results from GPS measurements carried out in NE India indicate that about 15–20 mm/yr of convergence is being accommodated there. Balanced-cross sections from the NE Himalaya indicate about 350–500 km of shortening south of the South Tibet Detachment (STD). Geothermobarometry suggest that the rocks south of the STD deformed under peak metamorphic conditions at ∼ 22 Ma. This indicates a geological convergence rate of ∼ 16–22 mm/yr which appears to be fairly consistent with the GPS derived convergence rates. Approximately 1.5 to 3.5 mm/yr (∼ 10–20 %) of the total N-S of the present-day convergence in the NE Himalaya is accommodated in the Shillong Plateau. In addition, ∼ 8–9 mm/yr of E-W convergence is observed in the eastern and central parts of the Shillong Plateau relative to the Indo-Burman fold-thrust belt. Balanced cross-sections in the Indo-Burman wedge together with higher resolution GPS measurements are required in the future to build on the first-order results presented here.  相似文献   

Biogeochemistry and paleoclimate variability during the Holocene: a record from Mansar Lake,Lesser Himalaya     

Brijraj Krishna Das  Birgit-Gaye  M. A. Malik 《Environmental Earth Sciences》2010,61(3):565-574

Investigation of biogeochemistry and amino acids on a 30-m-long core from Mansar Lake has thrown light on palaeoclimate variability during the Holocene period. The C/N ratio between 6 and 10 with some deviations and δ13C mostly between −20 and −22‰ in the shallow core, as well as a C/N ratio greater than 13 reaching from 19 to 20 and correspondingly lower δ13C of –28‰ in the deeper core suggest an aquatic source of carbon in the former and a cellulose-rich land plant source in the latter. This is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core, which indicates a hot and wet climatic regime during the early Holocene and dry and cold during the late Holocene period. The amino acid data AA-C/C% and AA-N/N% are higher in shallow sediments compared to deeper sediments, indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core. The lower percentage of the non-protein amino acids β-alanine (ALA) and γ-amino-butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin. The higher amino acid ratio Asp/β-Ala (16.99 av.) and Glu/γ-Aba (18.18 av.) in the shallow core and lower ratios (10.32 and 12.41 av.) in the deeper core, and Asp/Glu (1.52 av.) and β-Ala/γ-Aba (1.61 av.) ratios in the former, which are potential indicators of the nature of the organic matter, are higher in the shallow core relative to the deeper core (1.33 and 1.23 av.), indicating relative biodegradation of organic matter in deeper sediments. It has been observed that the organic matter associated with the dry season is relatively less biodegraded, as evidenced from their higher ratios, and is more biodegraded in the wet season as their ratios are lower in the river sediments. In the absence of a bacterial contribution of organic matter from the soil source in this lake, since Mansar Lake is a non-drainage type, it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments. Therefore, the C/N ratio and δ13C values supported by amino acid data, the latter being significant in revealing primary productivity and a terrestrial source of organic matter, suggest a hot and wet climatic regime during the early Holocene (ca. 7580 bp) and a dry and cold in the late Holocene period (ca. 4050 bp).  相似文献   

Periodicity in the solar wind velocity, temperature and number density     

T. K. Das  M. K. Ghosh 《Monthly notices of the Royal Astronomical Society》1999,310(2):414-418

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Chronology and sediment provenance of extreme floods of Siang River (Tsangpo-Brahmaputra River valley), northeast Himalaya     

Sandeep Panda  Anil Kumar  Satyabrata Das  Rahul Devrani  Santosh Rai  Kuldeep Prakash  Pradeep Srivastava 《地球表面变化过程与地形》2020,45(11):2495-2511

This study explores paleoflood deposits of the Siang River, known as the Tsangpo in Tibet. The river that often experiences large floods brings down huge amount of sediment and water that adversely affect the downstream regions with large human populations in the states of northeast Himalaya and its foreland. Along it's ~300 km mountainous stretch we collected samples for sedimentological, petrographic and Sr–Nd isotopic study to explore sediment provenance and dated the paleofloods (via optically stimulated luminescence, OSL). Geomorphic indices including precipitation and a geomorphic swath profile across the Brahmaputra catchment were studied to understand the interplay of mountain relief and rainfall that determine potential zones of high erosion and sediment supply. The OSL technique indicated the Siang River experienced at least eight large floods between 7 and 1 ka, possibly under the influence of warm and wet climatic conditions. The petrographic and isotopic data suggests that the eastern Himalayan syntaxis, which has the highest uplift and exhumation rate in the area, is not always the highest sediment producing zone. In some instances, the Tibetan plateau produces higher fluxes of sediments via glacial and landslide lake outburst floods (GLOFs and LLOFs). © 2020 John Wiley & Sons, Ltd.  相似文献   

Bed roughness and grain sorting-an experimental study over fine to medium sand beds     

Barendra Purkait  Dipanjan Das Majumdar  Rajat Mazumder 《国际泥沙研究》2017,32(3)

The relation between grain-size distribution of the bed and in suspension was critically examined under a uniform flow velocity of 50 cm/s over two beds: one of mainly fine sands and the other of medium sands. Two sections – one 2.85 m downstream and the other 6.35 m downstream in the experimental channel-were selected for sampling to study the grain-sorting pattern in the vertical direction along the direction of transport. The shape and type of the grain-size distribution pattern were critically studied with height above the bed. The change in the distribution pattern has been attributed to the change of local bed roughness causing scouring against the protruded relatively coarse grains on the bed. Such trends are important to predict the nature of river bed topography. The sand of Bed-1 initially exhibits a log-skew-Laplace distribution at different heights of suspension. The distribution pattern, however, changes but this changing pattern is not consistent along the upstream side. For Bed-2, which initially exhibits a log-normal distribution, the same pattern persists from the height of suspension at 5 cm up to 20 cm. Such consistency in log-normality is also observed at the downstream points of measurement. It is generally expected that the mean grain-size would reduce with increases of suspension height but the results of the experiments, in some occasions, differ significantly from the gradual fining upward trend. This result has been attributed to local changes of bed roughness arising from the protruded relatively coarse grains causing eddies, scouring, and turbulent phenomena which moves coarse particles higher in suspension adding a coarse tail to the distribution increasing the mean grain-size.  相似文献   

First record of microsporophyll genus Caytonanthus Thomas from Early Cretaceous beds of South Rewa Gondwana Basin,India: Its evolutionary and palaeogeographical significance          下载免费PDF全文

Neeru Prakash  Neelam Das 《Island Arc》2017,26(1)

Pteridosperms (seed ferns) are an extinct group of large and diverse plants. They were dominant elements during Palaeozoic and were also an important component in the Mesozoic vegetation but declined globally in the Cretaceous time with the radiation of angiosperms. The order Caytoniales of Mesozoic pteridosperm is an extinct group of seed ferns in the vegetation. They thrived for about 100 million years from the Late Triassic to the Late Cretaceous. Although they never attained dominant status, their rare occurrence in the vegetation is quite important and fascinating. For this extinct group of seed fern, Thomas ( 1925 ) erected a new order Caytoniales which includes three organ genera Caytonia (megasporophyll), Caytonanthus (microsporophyll) and Sagenopteris (leaves). This paper is aimed to document first record of microsporophyll genus Caytonanthus, obtained from the Lower Cretaceous beds of the South Rewa Gondwana Basin of the Indian Peninsula. Its morpho‐characters, palaeogeographic distribution, along with its plausible southern origin through ancestral group like Glossopteridales, are surmised here.  相似文献   

Seismic analysis of a curved bridge considering deck‐abutment pounding interaction: an analytical investigation on the post‐impact response          下载免费PDF全文

Arnab Banerjee  Avishek Chanda  Raj Das 《地震工程与结构动力学》2017,46(2):267-290

Horizontal curved bridges are very common at intersections and at the changing angle of bridge alignment. Almost in every previous earthquake report, it can be seen that the columns of a curved segment experience torsional damage, and the curved decks are unseated from the abutment support. The main reason behind that phenomenon is the in‐plane deck rotation which results because of the complex dynamic coupling between two longitudinal directional vibrations. The curved decks are susceptible to deck rotation because in a curved segment, the centre of mass and the centre of stiffness generally lie outside the bridge deck and are not located at the same point. The pounding with the abutment often increases the rotational tendency of the deck. In this paper, a classical mechanics‐based approach is adopted to analytically estimate the deck rotation potential of curved bridge considering the deck‐abutment pounding interaction. The deck‐abutment pounding is modelled using non‐smooth techniques considering the Newton's impact law in the normal and Coulomb's friction in the tangential direction. Within the scope of this paper, a parametric study is performed to get the ideal combination of the column and bent arrangement and the gap distance. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Quantification and spatial distribution of pore-filling materials through constrained rock physics template and fluid response modelling in Paleogene clastic reservoir from Cauvery basin,India     

Prabal Shankar Das  Rima Chatterjee  Sumangal Dasgupta  Ranajit Das  Debjani Bakshi  Mukesh Gupta 《Geophysical Prospecting》2019,67(1):150-166

Sands belonging to Kamalapuram Formation of Paleocene-Eocene age are deposited in Cauvery basin as incised valley fill during a regressive cycle. Here we attempt to quantify the influence of diagenesis on pore-filling materials using rock physics template constrained by geohistory modelling. Primarily, porosity–velocity and acoustic impedance – the ratio of P-wave and S-wave velocity (V_P/V_s) cross-plots are used as rock physics templates. Rock physics template has efficiently quantified pore-filling materials namely; contact cement and non-contact cement. The estimated contact cement and non-contact cement are correlated with conventional petrophysical logs within the selected depth interval. Further, this correlation is used to interpret the composition of pore-filling materials. Shallower depth intervals (I and II) exhibit moderate non-contact cement (4–5%) and insignificant contact cement (1–2% approx.) depositions. However, deeper interval (III) records a significant amount of pore-filling materials amounting average of 12% non-contact cement and 4% contact cement. Pore-filling materials demonstrate a positive correlation with the depth of burial. The fluid response is substantially affected by the degree of diagenesis, composition and spatial distribution of pore-filling materials. Shallower depth intervals (1770–1786 m and 1858–1878 m) are relatively more sensitive to fluid changes as it is affected by insignificant contact cement. The depth interval 1770–1786 m shows class II (oil) and class III (gas) amplitude variation with offset anomalies. The sand occurring in depth interval 1858–1878 m demonstrates class IIP (oil) and II (gas) anomaly. The deeper interval (2118–2170 m) is comparatively stiffer and demonstrates class I amplitude variation with offset (oil and gas sand) anomaly.  相似文献   

Intrinsic variability and field statistics for pulsars B1641–45 and B0950+08     

Iver H. Cairns  S. Johnston  P. Das 《Monthly notices of the Royal Astronomical Society》2004,353(1):270-286

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Solid waste management through multi-criteria decision making: using analytic hierarchy process as an assessment framework for the Hooghly district,West Bengal     

Das  Amit Kumar  Chatterjee  Uday  Mukherjee  Jenia 《GeoJournal》2022,87(4):911-930

Solid waste management (SWM) is a crucial service governed by urban local bodies (ULB). Hence, it is essential to identify challenges and opportunities in the SWM procedures and practices towards improved delivery of services. In this study, analytic hierarchy process (AHP) has been applied in the three sub-divisional towns of the Hooghly district, West Bengal (India), namely Chandannagar, Hooghly-Chinsurah and Serampore to analyze the existing SWM scenario. As AHP is a Multi-Criteria Decision Making tool, hence, it has been deployed by experts to come up with SWM performance index, clearly demonstrating the strengths and weaknesses of management strategies in selected study sites. This article further advances the significance of the AHP method by carving out multi-layered realities through the quantification of qualitative insights across various segments of waste management in the three towns. While interviews with waste management officials led to the formulation of key performance indicators and sub-indicators matrix, the obtained normalized weights brought to the fore the real engagement and actions executed by each of these towns in managing solid wastes. The application of this innovative AHP method ensured accuracy in the ranking system across performance of the specified ULBs. This AHP-induced situational analysis of SWM is not only significant in terms of policy formulation in the ULBs of the Hooghly district but has potentials to work at scales.

Graphical abstract

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