Repeated cycles of submarine channel incision, infill and transition to sheet sandstone development in the Alpine Foreland Basin, SE France     

William D. McCaffrey  Sanjeev Gupta†  Rufus Brunt 《Sedimentology》2002,49(3):623-635

The Grès de Champsaur turbidite system, deposited in a distal setting in the Alpine Foreland Basin of south‐eastern France, exhibits a repeated upsection alternation in sand body geometry between incised channels and sheet sands. The channels form symmetric lenticular erosional features, of width 900–1000 m (measured between the lateral limits of incision) and depth 65–115 m, and can be traced axially for up to 5 km. In each case, the channel fill is capped by a laterally persistent sandy sheet‐form interval, which lies upon a fine‐grained substrate beyond the channel margins. No intrachannel elements have been traced into the substrate sequence, suggesting that, before infill, the channels acted as open sea‐floor conduits of essentially the same dimensions as the preserved channel deposits. The channels are vertically stacked, although axial erosion juxtaposes younger channel axis deposits against the fill of older channels and their channel‐capping sheet sandstones to produce an apparently well‐connected composite sandstone body geometry. The predominant channel‐fill facies comprises coarse‐grained, amalgamated sandstones, which are commonly parallel‐ or cross‐stratified. Subsidiary facies of finer grained sandstone–mudstone couplets and clast‐bearing muddy debrites are commonly preserved as erosional remnants, suggesting a complex channel history of aggradation and erosion. The repeated cycles of channel incision, infill and transition to sheet sandstone development indicate repetitive incision and healing of the palaeo‐sea floor. A model is proposed that links incision to the development of relatively steep axial gradients (parallel to the mean dispersal direction) and the return to sheet‐form deposition to the re‐establishment of lower axial gradients, with the repetitive switch between incisional channels and sheet sandstones driven by changes in sediment input rate against a background of ongoing sea‐floor tilting.  相似文献   

Morphological and strength analysis of PCC bottom ash amended with bentonite     

Sanjeev Kumar  Sanjay Mishra  Manoj Mohanty  Bernard R. Schmitt  Prashanth Vaddu 《Geotechnical and Geological Engineering》2006,24(4):1009-1020

Within the last few years several studies have been completed to evaluate strength, stiffness, and durability properties of pulverized coal combustion (PCC) bottom ash mixed with various admixtures. Studies have shown that strength and stiffness of PCC bottom ash mixed with sodium bentonite changes with the increase in the curing period. Researchers have concluded that this change is due to the chemical composition of the bottom ash and bentonite. In order to understand the reasons for the change in characteristics of bottom ash-bentonite mixtures with time, the strength and structural characteristics of bottom ash-bentonite mixtures cured for various periods was evaluated. Results of the strength testing showed increase in strength and stiffness of the mixtures with curing period. The results of structural analysis using environmental scanning electron microscopy show development of fibrous elements which may cause increase in the unconfined compressive strength and stiffness of the mixtures with the curing period. Selected results from this study are presented herein.  相似文献   

Identification of Groundwater Potential Zones using Remote Sensing and GIS of K-J Watershed,India     

B. S. Chaudhary  Sanjeev Kumar 《Journal of the Geological Society of India》2018,91(6):717-721

Groundwater potential zone mapping has become easier with the inputs from Remote Sensing (RS) & Geographical Information System (GIS) techniques. Various thematic maps like geology, geomorphology, drainage density, slope, landuse/landcover etc can be easily generated through RS & GIS. The present study is aimed at generating groundwater potential map of Koshalya-Jhajhara (K-J) watershed by using integrated approach of RS & GIS. Various thematic layers have been generated and assigned weightages and ranks. These layers have been integrated in GIS software for generating Groundwater Potential Zone (GPZ) map of K-J watershed. The area falls into five categories of groundwater potential zones i.e. very good, good, moderate, poor and very Poor depending on the likelihood of availability of ground water. On the basis of this study it is found that only 5.83 km² and 4.91 km² area is under very good and good category of groundwater availability respectively. An area of 24.48 km² is found under moderate category whereas dominant portion of K-J watershed i.e. 61.83 km² and 37.87 km² area falls under poor and very poor category of availability of groundwater respectively.  相似文献   

On the rainfall asymmetry and distribution in tropical cyclones over Bay of Bengal using TMPA and GPM rainfall products     

Manoj Kumar Thakur  T. V. Lakshmi Kumar  Sanjeev Dwivedi  M. S. Narayanan 《Natural Hazards》2018,94(2):819-832

In the present study, we have used TRMM multi-satellite precipitation analysis (TMPA) 3B42 and global precipitation mission (GPM): IMERG “precipitation Cal” products to identify and quantify the asymmetry and distribution of rainfall in tropical cyclones formed over Bay of Bengal (BoB). For the period 2010–2013, TMPA products have been made use of and for the period 2014–2017, GPM–IMERG products are used to study the aforementioned features. Overall, 17 cyclones covering 75 events/days ranging from depression to very severe cyclonic stage of the system have been analysed. Our analysis revealed some interesting features on asymmetry, direction of maximum rain-receiving zones, relation of T-number with maximum and total rainfall in rain-receiving areas. The study reveals the direction of rainfall zone is mostly towards west and southwest directions of the storm centre in BoB. This point gains importance in the context of earlier reports, where it is mentioned that the direction of maximum rainfall is in east. The study also infers that the maximum rainfall and total rainfall need not be dependent on the intensity (indicated by T-number). We also attempted to classify the rain-receiving zones, based on both the rainfall-rate window and area covered in each window of rainfall, and a criterion has been proposed. The distribution of rainfall is classified, as sharply falling, slowly falling and nearly constant.  相似文献   

Theoretical/numerical model for the transport of non-uniform suspended sediment in open channels   总被引：2，自引：0，他引：2  

Sanjeev K. Jha  Fabián A. Bombardelli 《Advances in water resources》2011,34(5):577-591

In this paper, we address the transport of multi-disperse suspended sediment mixtures in open channels, via the use of the two-fluid model. To that end, we extend previously developed frameworks for the dilute and non-dilute transport of suspended sediment. Within the scope of the Reynolds-averaged Navier-Stokes (RANS) equations, these modeling frameworks comprise mass and momentum equations for both phases (water and sediment). Here, we calculate the distribution of total volumetric concentration of sediment using two approaches: (1) by considering the mixture as represented by a single size; we call this approach Partial two-fluid model for uniform sediments (PTFMU); and (2) by combining the volumetric concentration of the sediment corresponding to several particle size classes; we call this approach Partial two-fluid model for non-uniform sediments (PTFMNU). In the second approach, we propose a methodology for the computation of the overall velocity of the disperse phase as a function of the velocities of each size class. k-ε type closures to account for the turbulence in the carrier phase (water) are applied. We also consider the coupling between the two phases through the drag force. Velocities of the carrier and disperse phases, and concentrations for each sediment class size are numerically solved by integrating the differential equations over control volumes. In order to validate our models, we compare numerical results to experimental data of Einstein and Chien [H.A. Einstein, N. Chien, Effects of heavy sediment concentration near the bed on velocity and sediment distribution, MRD sediment series report, University of California, Berkley, 1955] and Taggart et al. [W.C. Taggart, C.A. Yermoli, S. Montes, A. Ippen, Effects of sediment size and gradation on concentration profiles for turbulent flow, Massachusetts Institute of Technology, 1972]. Results of mean velocity of the carrier phase are in close agreement with the experimental data. For the prediction of sediment concentrations, we observe that there is a difference in the results using the two approaches mentioned above. We additionally obtain values of the Schmidt number needed to improve the agreement between predictions of the distribution of suspended sediment and the experimental data, and discuss the effect of sediment size and increasing sediment concentration on the values of the Schmidt number.  相似文献   

Status of NCEP CFS vis-a-vis IPCC AR4 models for the simulation of Indian summer monsoon     

Samir Pokhrel  Ashish Dhakate  Hemantkumar S. Chaudhari  Subodh K. Saha 《Theoretical and Applied Climatology》2013,111(1-2):65-78

National Centers for Environmental Prediction (NCEP) Coupled Forecast System (CFS) is selected to play a lead role for monsoon research (seasonal prediction, extended range prediction, climate prediction, etc.) in the ambitious Monsoon Mission project of Government of India. Thus, as a prerequisite, a detail analysis for the performance of NCEP CFS vis-a-vis IPCC AR4 models for the simulation of Indian summer monsoon (ISM) is attempted. It is found that the mean monsoon simulations by CFS in its long run are at par with the IPCC models. The spatial distribution of rainfall in the realm of Indian subcontinent augurs the better results for CFS as compared with the IPCC models. The major drawback of CFS is the bifurcation of rain types; it shows almost 80–90 % rain as convective, contrary to the observation where it is only 50–65 %; however, the same lacuna creeps in other models of IPCC as well. The only respite is that it realistically simulates the proper ratio of convective and stratiform rain over central and southern part of India. In case of local air–sea interaction, it outperforms other models. However, for monsoon teleconnections, it competes with the better models of the IPCC. This study gives us the confidence that CFS can be very well utilized for monsoon studies and can be safely used for the future development for reliable prediction system of ISM.  相似文献   

Role of convective and microphysical processes on the simulation of monsoon intraseasonal oscillation     

Dutta  Ushnanshu  Chaudhari  Hemantkumar S.  Hazra  Anupam  Pokhrel  Samir  Saha  Subodh Kumar  Veeranjaneyulu  Chinta 《Climate Dynamics》2020,55(9-10):2377-2403

Climate Dynamics - The study explores the role of ice-phase microphysics and convection for the better simulation of Indian summer monsoon rainfall (ISMR) and monsoon intraseasonal oscillation...  相似文献   

Mushrooms in the Mountains: Assessing the Role of Fungi on the Ecosystem-based Adaptation (EbA) Practices in Nepal Himalaya     

DEVKOTA Shiva  SHRESTHA Uttam Babu  POUDEL Sanjeev  CHAUDHARY Ram Prasad 《资源与生态学报(英文版)》2022,13(6):1030-1036

To achieve the Sustainable Development Goals (SDGs), thereby meet the post 2020 global biodiversity targets and increase resilience to climate change, nature-based approaches such as ecosystem-based adaptation (EbA) is suggested as a promising and integrated adaptation strategy. EbA comprises adaptation strategies that value the role of ecosystems in reducing social vulnerability to climate change. Among the different biological groups on earth, fungi play not only an important role to maintain the biogeochemical cycle/nutrient cycle in ecosystems (supporting and regulating services), but also contribute to the socio-economic and cultural benefits of societies (provisioning and cultural services). Here, we present our knowledge and scientific understanding on how these neglected groups of biodiversity-fungi are crucial for ecosystem-based adaptation (EbA) approach based on our field experience, review and associated expertise on caterpillar fungus (Ophiocordyceps sinensis), and other wild mushrooms found in Nepal. Several species of fungi are used by local communities as food, medicines, and environmental income. Fungi are important sources of household income for mountain communities in Nepal providing a cushion during shocks and disasters and supporting food security, health care, education and building shelter. For the holistic EbA approach, it is essential to strengthen local institutions as well as indigenous local knowledge which could be an important policy intervention for the identification, conservation, and sustainable management of ecologically, socially and economically useful fungal species.  相似文献   

Crustal deformation rates in Assam Valley,Shillong Plateau,Eastern Himalaya,and Indo-Burmese region from 11 years (2002–2013) of GPS measurements     

Barman  Prakash  Jade  Sridevi  Shrungeshwara  T. S.  Kumar  Ashok  Bhattacharyya  Sanjeev  Ray  Jagat Dwipendra  Jagannathan  Saigeetha  Jamir  Wangshi Menla 《International Journal of Earth Sciences》2017,106(6):2025-2038

International Journal of Earth Sciences - The present study reports the contemporary deformation of the tectonically complex northeast India using 11 years (2002–2013) of GPS...  相似文献   

Rayleigh waves in liquid layer resting over an initially stressed orthotropic half-space under self-weight     

Sanjeev Anand Sahu  Soniya Chaudhary  Pradeep Kumar Saroj  Amares Chattopadhyay 《Arabian Journal of Geosciences》2017,10(5):120

The study of surface waves (Rayleigh wave) finds their virtuous applications in a numerous geological and geophysical fields including water, oil, gas, and other subsurface geological probing and exploration. The present paper efforts to investigate the influence of initial stress, Earth magnetism, and gravity on propagation of Rayleigh waves. Considered model is consist of a liquid layer lying over a magnetoelastic orthotropic half-space under self-weight and initial stress. Method of separation of variable is used to solve the equation of motion. Solutions of governing equations are obtained in terms of displacement. Frequency relation for Rayleigh wave has been obtained and matched with classical Rayleigh wave equation. In addition to classical case, some existing results have been deduced as particular case of the present study. Obtained results have been shown through numerical illustrations. It is found that the considered parameters (initial stress, Earth magnetism, and gravity) have prominent effect on phase velocity of Rayleigh wave. Graphical representations have been made to exhibit the velocity profile of Rayleigh waves for different cases with the help of MATHEMATICA. The present study may be useful for seismologists and engineers who are concern with applications of wave propagation in magnetoelastic orthotropic medium.  相似文献