Peperite occurrence and its implications on origin and temporal development of the Proterozoic Dhala basin,Mohar area,Shivpuri district,Madhya Pradesh     

K. K. Sinha  Pradeep Pandey  C. L. Bhairam  P. S. Parihar 《Journal of the Geological Society of India》2011,77(2):183-189

In the western part of Bundelkhand massif, a caldera with intra-caldera sediments, known as Dhala Formation, occurs as an outlier in and around Mohar village of Shivpuri district, Madhya Pradesh. For the first time, occurrence of peperite is being reported from the basal part of the Dhala sediment. Two types of peperites have been recognized: blocky and fluidal or globular with variable morphology. In peperitic zones, features like soft sediment deformations, presence of sediment into the rhyolite along cracks, vesiculation of the sediments and other evidences suggestive of sediment fluidization are some definite characteristics of interaction of hot magma with wet sediments forming peperite. The occurrence of peperites reflects the contemporaniety of deposition of the Dhala sediments and volcanism, which is well in accordance to the volcanic origin of Dhala structure. Further, the nature of unconformity between the Dhala and overlying Kaimur which is characterized by merely a few centimeter thick pebbly/conglomeratic bed does not appear to represent a large hiatus as expected between the Semri and Kaimur of Vindhyan Supergroup. So, the contemporaniety of the Dhala Formation (at least the lower part) as reflected by occurrence of peperites, coupled with the available age of the rhyolite and the nature of the unconformity between the Dhala and overlying Kaimur provide convincing evidence to correlate the Dhala Formation with the Lower part of the Kaimur and unlikely with the Semri Group or Bijawar as proposed earlier.  相似文献   

A global context for megadroughts in monsoon Asia during the past millennium   总被引：1，自引：0，他引：1  

Ashish Sinha  Lowell Stott  Max Berkelhammer  Hai Cheng  R. Lawrence Edwards  Brendan Buckley  Mark Aldenderfer  Manfred Mudelsee 《Quaternary Science Reviews》2011,30(1-2):47-62

Proxy reconstructions of precipitation from central India, north-central China, and southern Vietnam reveal a series of monsoon droughts during the mid 14th–15th centuries that each lasted for several years to decades. These monsoon megadroughts have no analog during the instrumental period. They occurred in the context of widespread thermal and hydrologic climate anomalies marking the onset of the Little Ice Age (LIA) and appear to have played a major role in shaping significant regional societal changes at that time. New tree ring-width based reconstructions of monsoon variability suggest episodic and widespread reoccurrences of monsoon megadroughts continued throughout the LIA. Although the El-Niño Southern Oscillation (ENSO) plays an important role in monsoon variability, there is no conclusive evidence to suggest that these megadroughts were associated with anomalous sea surface temperature anomalies that were solely the result of ENSO-like variability in the tropical Pacific. Instead, the causative mechanisms of these megadroughts may reside in protracted changes in the synoptic-scale monsoon climatology of the Indian Ocean. Today, the intra-seasonal monsoon variability is dominated by ‘active’ and the ‘break’ spells – two distinct oscillatory modes of monsoon that have radically different synoptic scale circulation and precipitation patterns. We suggest that protracted locking of the monsoon into the “break-dominated” mode – a mode that favors reduced precipitation over the Indian sub-continent and SE Asia and enhanced precipitation over the equatorial Indian Ocean, may have caused these exceptional droughts. Impetus for periodic locking of the monsoon into this mode may have been provided by cooler temperatures at the extratropical latitudes in the Northern Hemisphere which forced the mean position of the Inter-Tropical Convergence Zone (ITCZ) further southward in the Indian Ocean.  相似文献   

Observations of PC5 pulsations near field-aligned current regions     

Alexander Z. Bochev  Karel Kudela  Iren A. Dimitrova  Petko Nenovski  Ashwini K. Sinha  Marián Slivka 《Studia Geophysica et Geodaetica》2009,53(4):537-556

Examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere, observed by INTERBALL-Auroral satellite during January 11, April 11 and June 28, 1997 are shown. Identification of corresponding magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured simultaneously onboard the spacecraft. The examined Pc5 pulsations reveal a compressional character. A fairly good correlation is demonstrated between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The ULF Pc5 wave occurrence is observed in both upward and downward FACs.  相似文献   

利用大地电磁资料对玄武岩成像的可行性     

Dhananjai Pandey　Lucy MacGregor　Martin Sinha　Satish Singh 《应用地球物理》2008,5(1):74-82

The magnetotelluric （MT） method has been among the favorite supporting tools for seismic imaging of sub-salt and sub-basalt targets. In this paper we present an example from Kachchh, India （where basaltic rocks overlie Mesozoic sedimentary rocks）, and discuss the feasibility of using MT method as an exploration tool in this geological setting. Our results highlight the difference in magnetotelluric response caused by the thin intrabasalt layering. The key issue addressed in this paper is what MT can and cannot provide in such geological settings. First, we compute apparent resistivity and phase response curves using representative resistivity-depth models and borehole data from the study area. Later, we compare these results to assess the plausibility of using MT to image the sub-volcanic sediments at Kachchh. Finally, we substantiate our discussion through one-dimensional inversion of the field observed MT data from this region that exhibits poor sensitivity of MT for thin basalt layers.  相似文献   

Prediction of SST anomalies of east Pacific Ocean (Nino 3 region) using a statistical model     

A. K. Srivastava  K. C. Sinha Ray 《Theoretical and Applied Climatology》2000,66(3-4):131-138

Summary  Average SST anomalies of OCT-DEC months for Nino-3 region are predicted using the following parameters – (i) April rain over Himachal Pradesh, (ii) Darwin pressure change (January–April), (iii) Southern Oscillation Index (Tahiti–Darwin) and (iv) SST anomalies of Nino-3 region in the month of May. Principal component analysis is used to orthogonalise the predictors before using them in the regression equation. The first two principal components, which explain nearly 73% of the variance, are used to fit a regression line. The period 1951–1985 is used as the calibration period for the model and the period 1986–1997 as the verification period for the forecast. The Brier score with respect to a reference forecast (persistence) for the independent period is found to be 0.82 which is indicative of good forecast skill. Received April 1, 1999 Revised January 17, 2000  相似文献   

Variational method for objective analysis of scalar variable and its derivative     

S. G. Narkhedkar  S. K. Sinha 《Journal of Earth System Science》2008,117(5):621-635

In this study real time data have been used to compare the standard and triangle method by performing the objective analysis of mean sea level pressure. In the standard method, derivative fields are obtained from the grid point data using finite difference scheme whereas in the triangle method, a set of non-overlapping triangles are formed from the observations and the scalar and the spatial derivatives are computed directly at the centroid of each of the non-overlapping triangles. These scalars and their derivatives are then mapped to uniform grids by using the standard method. It has been found that objectively analysed scalar field obtained using standard method is superior to the scalar field derived by the triangle method, whereas the derivative fields produced by triangle method are superior to the derivative fields produced using standard method. A variational objective analysis scheme has been developed and an experiment has been carried out with depression case of June (11–15) 2004. It is found that the new scheme (variational) is able to extract the better parts of both triangle and standard methods. The results of this study will be useful in carrying out diagnostic calculations that involve derivative estimates.  相似文献   

Flood risk analysis in the Kosi river basin, north Bihar using multi-parametric approach of Analytical Hierarchy Process (AHP)   总被引：3，自引：0，他引：3  

R. Sinha  G. V. Bapalu  L. K. Singh  B. Rath 《Journal of the Indian Society of Remote Sensing》2008,36(4):335-349

The Kosi river in north Bihar plains, eastern India presents a challenge in terms of long and recurring flood hazard. Despite a long history of flood control management in the basin for more than 5 decades, the river continues to bring a lot of misery through extensive flooding. This paper revisits the flooding problem in the Kosi river basin and presents an in-depth analysis of flood hydrology. We integrate the hydrological analysis with a GIS-based flood risk mapping in parts of the basin. Typical hydrological characteristics of the Kosi river include very high discharge variability, and high sediment flux from an uplifting hinterland. Annual peak discharges often exceed the mean annual flood and the low-lying tracts of the alluvial plains are extensively inundated year after year. Our flood risk analysis follows a multi-parametric approach using Analytical Hierarchy Process (AHP) and integrates geomorphological, land cover, topographic and social (population density) parameters to propose a Flood Risk Index (FRI). The flood risk map is validated with long-term inundation maps and offers a cost-effective solution for planning mitigation measures in flood-prone areas.  相似文献   

Land use change analysis of Bharatpur district using GIS     

P S Dhinwa  S K Pathan  S V C Sastry  Mukund Rao  K L Majumder  M L Chotani  J Premnath Singh  R L P Sinha 《Journal of the Indian Society of Remote Sensing》1992,20(4):237-250

Knowledge on area and distribution of land uses plays an important role in district planning. An attempt has been made here to study existing land use pattern and changes in the land use pattern of Bharatpur district. Multi-date remote sensing data (1986 and 1989) has been used for the purpose. Seventeen land use maps on 1∶50,000 scale were prepared. ARC/INFO GIS package has been employed for the land use analysis. GIS package has also been used to relate the land use information to the villages and arrive at tentative comparison of land use as is reported in Census and as obtained from the remote sensing. Major findings in land use pattern of Bharatpur district are a) that the land use pattern in Bharatpur district is not similar to that of general land use pattern prevalent in Rajasthan State as a whole, b) Agriculture is the predominant user of land occupying about 75 percent of the reporting area, c) Forest cover in the district is not very significant and it has been depleted from 5.6 percent to 3.1 percent, d) the area under pastures and tree crops is also negligible and e) Area under waste land (eroded land, undulating terrain with or without scrub and rock out crops has been increased from 6.34 percent to 7.89 percent. The area under salt affected land, sandy area and water logged area has been decreased from 6.83 percent to 2.09 percent.  相似文献   

Bathymetry of the Reykjanes Ridge     

Keeton  J. A.  Searle  R. C.  Peirce  C.  Parsons  B.  White  R. S.  Sinha  M. C.  Murton  B. J.  Parson  L. M. 《Marine Geophysical Researches》1997,19(1):55-64

We present a series of 1:200,000 scale maps of the bathymetry of the Reykjanes Ridge. The data are divided into four maps, extending 630 km along the ridge axis and between 30 and 100 km off-axis. This compilation of bathymetry data is extremely detailed, gridded at approximately 100 m resolution, and with almost no gaps. The Reykjanes Ridge is one of the best examples of a hotspot-dominated ridge, whose characteristics are influenced by its proximity to the Iceland plume. Many fundamental questions may be addressed at the Reykjanes Ridge, which is why the BRIDGE programme identified it as one of its four regional projects. These maps represent a BRIDGE contribution to the general scientific community.  相似文献   

Statistical Simulation of Boxing Day Tsunami of The Indian Ocean and a Predictive Equation for Beach Run up Heights Based on Work-Energy Theorem     

G. Muraleedharan  Mourani Sinha  A. D. Rao  T. S. Murty 《Marine Geodesy》2006,29(3):223-231

The tsunami similar to the one that has occurred in December 26, 2004 (Boxing Day Tsunami) in the Indian Ocean is simulated using the expression derived from Modified Weibull Distribution (for maximum wave height simulation) for extreme wave height predictions. The tuning coefficient plays a significant role in estimating the tsunami heights at various stages. It follows well defined mathematical laws at different stages. It is time dependent in the first three stages and depth dependent in the last two stages. The beach run-up heights estimated by the expression derived from the work-energy relation are comparable with observed values with reasonable accuracy.  相似文献