Experimental decipherment of the soft-sediment deformation observed in the upper part of the Talchir Formation (Lower Permian), Jharia Basin, India     

Prabir Dasgupta   《Sedimentary Geology》2008,205(3-4):100-110

Four types of soft-sediment folds of distinct geometry can be recognized in the upper part of the Talchir Formation (Lower Permian) of Jharia Basin, India. These folds, on systematic examination, indicate some events of progressive deformation. Experimental study reveals that if a layered stack of clay and overlying sand is allowed to flow slowly down a slope, differential velocity due to viscosity contrast leads to the deformation of the rheologic interface. The sharp planar contact gradually becomes wavy leading to the development of round-hinged folds involving sediments adjacent to it. With the advancement of the flow these folds gradually become overturned with the rotation of the axial plane in the direction of flow. Computer simulation suggests that progressive deformation of these folds by simple shearing may lead to the formation of tight isoclinal folds, which on dislocation along intrastratal normal faults may lead to the development of rootless isoclinal folds. The sheath folds observed in the studied section also indicate accentuation of the curved hinge due to simple shearing. The spatial distribution of these fold types in conjunction with the inferred direction of progressive deformation indicate basinward translation of the slump slice. If the same stack of sediments rapidly flows down the slope, the waveform generated at the interface quickly breaks in the form of roll-up recumbent fold due to Kelvin–Helmholtz instability.  相似文献   

Proterozoic East Gondwana: Supercontinent Assembly and Breakup     

M. Yoshida  B.F. Windley  S. Dasgupta 《Gondwana Research》2003,6(4):960

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When 4D seismic is not applicable: Alternative monitoring scenarios for the Arab-D reservoir in the Ghawar Field     

Shiv N. Dasgupta 《Geophysical Prospecting》2005,53(2):215-227

Ghawar, the largest oilfield in the world, produces oil from the Upper Jurassic Arab‐D carbonate reservoir. The high rigidity of the limestone–dolomite reservoir rock matrix and the small contrast between the elastic properties of the pore fluids, i.e. oil and water, are responsible for the weak 4D seismic effect due to oil production. A feasibility study was recently completed to quantify the 4D seismic response of reservoir saturation changes as brine replaced oil. The study consisted of analysing reservoir rock physics, petro‐acoustic data and seismic modelling. A seismic model of flow simulation using fluid substitution concluded that time‐lapse surface seismic or conventional 4D seismic is unlikely to detect the floodfront within the repeatability of surface seismic measurements. Thus, an alternative approach to 4D seismic for reservoir fluid monitoring is proposed. Permanent seismic sensors could be installed in a borehole and on the surface for passive monitoring of microseismic activity from reservoir pore‐pressure perturbations. Reservoir production and injection operations create these pressure or stress perturbations. Reservoir heterogeneities affecting the fluid flow could be mapped by recording the distribution of epicentre locations of these microseisms or small earthquakes. The permanent borehole sensors could also record repeated offset vertical seismic profiling surveys using a surface source at a fixed location to ensure repeatability. The repeated vertical seismic profiling could image the change in reservoir properties with production.  相似文献   

Optimization and Parametrical Investigation to Assess the Reconstitution of Different Types of Indian Sand Using Portable Travelling Pluviator     

V.?Srinivasan  Shubham?Srivastava  Priyanka?GhoshEmail author 《Geotechnical and Geological Engineering》2016,34(1):59-73

By using the air pluviation technique, it is aimed to achieve the desired relative density with uniform void ratio throughout the specimen in order to maintain the homogeneity and to avoid the spatial variability. Further, in order to achieve the maximum deposition intensity, a systematic optimization study has been carried out rigorously in a test tank to determine the diameter of the orifice to be employed for the sieve plates of different porosity and the number of sieve plates to be installed in the diffuser sieve sets. The study has been conducted with four different patterns of sieves with different porosity to achieve a wide range of relative densities for four different uniformly graded Indian sands. The dynamic penetrometer which is considered to be one of the cost effective instruments has been efficiently used to determine the soil resistance at various locations of the test tank for every given height of fall in order to check the uniformity of placement density throughout the sand bed. The study reveals that the sand beds of different relative densities could be achieved using different patterns of diffuser sieves at optimum sand flow rate without compromising the uniformity. The effect of height of fall as well as porosity of diffuser sieves on the relative density of different sands has been studied in detail. The deposition intensity and the relative density obtained from the present study are compared with the values available in the literature.  相似文献   

Identifying source and evaluation of hydrogeochemical processes in the hard rock aquifer system: geostatistical analysis and geochemical modeling techniques     

N. Janardhana Raju  Priyanka Patel  B. C. Sundara Raja Reddy  U. Suresh  T. V. K. Reddy 《Environmental Earth Sciences》2016,75(16):1157

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Impact of artificial subsurface drainage on groundwater travel times and baseflow discharge in an agricultural watershed,Iowa (USA)     

Keith E. Schilling  Priyanka Jindal  Nandita B. Basu  Matthew J. Helmers 《水文研究》2012,26(20):3092-3100

Pollutant delivery through artificial subsurface drainage networks to streams is an important transport mechanism, yet the impact of drainage tiles on groundwater hydrology at the watershed scale has not been well documented. In this study, we developed a two‐dimensional, steady‐state groundwater flow model for a representative Iowa agricultural watershed to simulate the impact of tile drainage density and incision depth on groundwater travel times and proportion of baseflow contributed by tile drains. Varying tile drainage density from 0 to 0.0038 m^?1, while maintaining a constant tile incision depth at 1.2 m, resulted in the mean groundwater travel time to decrease exponentially from 40 years to 19 years and increased the tile contribution to baseflow from 0% to an upper bound of 37%. In contrast, varying tile depths from 0.3 to 2.7 m, while maintaining a constant tile drainage density of 0.0038 m^?1, caused mean travel times to decrease linearly from 22 to 18 years and increased the tile contribution to baseflow from 30% to 54% in a near‐linear manner. The decrease in the mean travel time was attributed to decrease in the saturated thickness of the aquifer with increasing drainage density and incision depth. Study results indicate that tile drainage affects fundamental watershed characteristics and should be taken into consideration when evaluating water and nitrate export from agricultural regions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Genetic reinterpretation of crystallographicintergrowths of jacobsite andhausmannite from natural assemblages     

Dr. Somnath Dasgupta  P. K. Bhattacharya  G. Chattopadhyay  M. Fukuoka  H. Banerjee  Supriya Roy 《Mineralogy and Petrology》1987,37(2):109-116

Summary Crystallographic intergrowths of jacobsite and hausmannite (vredenburgite) occur in association with braunite in the Precambrian Sausar Group of rocks, India, that were metamorphosed under 600-700°C and P 6 kb. Quartz, hematite, rhodochrosite and a later hausmannite may occasionally occur as minor associates. Detailed characterization of the intergrown phases reveals that hausmannite lamellae, oriented in 4 or 5 crystallographic directions in the jacobsite host, show a wide variation in thickness and tapered intersections at low angles. The lamellae may be locally deformed. Analytical data reveal that the composition of natural hausmannite and jacobsite in the intergrowths cannot be approximated within the system Fe₃O₄ -Mn₃O₄, as has been conventionally done. These really belong to the Fe₂O₃-Mn₃O₄ subsystem. In the two phase intergrowths, hausmannite is depleted and the jacobsite is enriched in Fe in higher grade rocks. Mineral associations and petrographic considerations suggest that the jacobsite-hausmannite intergrowth originated through prograde decarbonation-oxidation reactions of a carbonatic precursor in an unbuffered X CO₂ situation, but f O₂ was held between hematite-magnetite and bixbyite-hausmannite buffers at the ambient physical conditions of metamorphism. Subsequent oxidation yielded a strong oxygenbuffering assemblage jacobsite, hausmannite, braunite, hematite and quartz. This study negates the commonly held idea that hausmannite jacobsite crystallographic intergrowth (vredenburgite) originates through unmixing of a high ([ldvredenburgite) originates through unmixing of a high temperature spinel_ss temperature spinel_ss during cooling.

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Genetische Reinterpretation der kristallographischen Verwachsungen von Jakobsit und Hausmannit in natürlichen Vorkommen

Zusammenfassung Kristallographische Verwachsungen von Jakobsit und Hausmannit (Vredenburgit) treten in Verbindung mit Braunit in Gesteinen der präkambrischen Sausargruppe in Indien auf. Die Gesteine wurden bei Drucken von ca. 6 kbar und Termperaturen von 600–700°C metamorphosiert. Quarz, Hämatit, Rhodochrosit, und Hausmannit als Spätphase treten gelegentlich als untergeordnete Gemengteile auf. Hausmannit-Lamellen, die in vier oder fünf kristallographischen Richtungen in Jakobsit orientiert sind, haben sehr unterschiedliche Durchmesser und bilden versetzte Zwickel in kleinem Winkel mit dem Jakobsit. Die Lamellen können lokal deformiert sein. Analytische Daten zeigen, daß die Zusammensetzung von natürlichem Hausmannit und Jakobsit in Verwachsungen nicht, wie bisher angenommen, in dem System Fe₃O₄-Mn₃O₄ dargestellt werden kann. Diese Verwachsungen gehören vielmehr in das Fe₂O₃-Mn₃O₄ System. In höher-gradigen metamorphen Gesteinen ist Fe in zwei-phasigen Verwachsungen im Hausmannit ab- und im Jakobsit angereichert. Die Mineralzusammensetzung und petrographische Gesichtspunkte lassen darauf schließen, daß die Jakobsit/Hausmannit Verwachsung durch prograde Dekarbonatisierung/Oxydationsreaktion eines karbonatischen Vorläufers in einem nicht gepufferten X CO₂ Milieu entstanden ist. F O₂ wurde durch Hämatit-Magnetit und Bixbyit-Hausmannit Puffer unter den gegebenen physikalischen Bedingungen der Metamorphose stabil gehalten. Eine nachfolgende Oxydation führte zu einer starken Sauerstoff-puffernden Assoziation von Jakobsit, Hausmannit, Braunit, Hämatit und Quarz. Diese Untersuchungen widerlegen die allgemein verbreitete Ansicht, daß die kristallographische Verwachsung von Hausmannit und Jakobsit (Vredenburgit) durch Entmischung eines Hochtemperatur-Spinells während der Abkühlung entstanden ist.

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Soil,landuse and land evaluation studies of Patna area Bihar     

M. L. Manchanda  Jitendra Prasad  H. S. Iyer  R. S Shukla  S. Dasgupta 《Journal of the Indian Society of Remote Sensing》1982,10(3):55-67

The soil and landuse surveys have been conducted in Patna area, Bihar, using aerial photos of 1:25,000 scale. Three major systems, Ganges Gandak and interfluvial plain, have been identified in the area. These were further sub-divided into levees plains and channels etc. The soils were classified according to Soil axonomy. The major land use of the area is cultivation (62.2%) (Upland, lowland and wet land crops) plantation (1.8%) habitation (16.0%), water bodies (8.8%), barren lands (9.4%) and miscellaneous (1.8%). The soils of the area have been evaluated for different land utilization types-upland crops, lowland crops, and habitation. For paddy 75.:%, upland crops 8.2% and for habitation 57%, area was found suitable.  相似文献   

Seismic Passive Earth Pressure Behind Non-vertical Retaining Wall Using Pseudo-dynamic Analysis   总被引：3，自引：0，他引：3  

Priyanka Ghosh 《Geotechnical and Geological Engineering》2007,25(6):693-703

This paper shows a detailed study on the seismic passive earth pressure behind a non-vertical cantilever retaining wall using pseudo-dynamic analysis. A planar failure surface has been considered behind the retaining wall. The effects of soil friction angle, wall inclination, wall friction angle, horizontal and vertical earthquake acceleration on the passive earth pressure have been explored. Unlike the Mononobe–Okabe method, which incorporates pseudo-static analysis, the present analysis predicts a nonlinear variation of passive earth pressure along the wall. The results have been thoroughly compared with the existing values in the literature.  相似文献   

Imaging Offsets in the Moho: Synthetic Tests using Gaussian Beams with Teleseismic Waves     

Robert L. Nowack  Wang-Ping Chen  Ulrich Kruse  Saptarshi Dasgupta 《Pure and Applied Geophysics》2007,164(10):1921-1936

We carry out a sequence of numerical tests to understand conditions under which rapid changes in crustal thickness can be reliably imaged by teleseismic body waves. Using the finite-difference method over a 2-D grid, we compute synthetic seismograms resulting from a planar P-wavefield incident below the grid. We then image the Moho using a migration scheme based on the Gaussian beam representation of the wavefield. The use of Gaussian beams for the downward propagation of the wavefield is particularly advantageous in certain geologically critical cases such as overthrusting of continental lithosphere, resulting in the juxtaposition of high-velocity mantle material over crustal rocks. In contrast to ray-based methods, Gaussian beam migration requires no special treatment to handle such heterogeneities. Our results suggest that with adequate station spacing and signal-to-noise ratios, offsets of the Moho, on the order of 10 km in height, can be reliably imaged beneath thickened crust at depths of about 50 km. Furthermore, even sharp corners and edges are faithfully imaged when precise values of seismic wave speeds are available. Our tests also demonstrate that flexibility in choices of different types of seismic phases is important, because any single phase has trade-offs in issues such as spatial resolution, array aperture, and amplitude of signals.  相似文献