Recent history of trends in vegetation greenness and large-scale ecosystem disturbances in Eurasia   总被引：1，自引：0，他引：1  

CHRISTOPHER POTTER  VIPIN KUMAR  STEVEN KLOOSTER  RAMAKRISHNA NEMANI 《Tellus. Series B, Chemical and physical meteorology》2007,59(2):260-272

  相似文献   

EFFECT OF VERTICAL CONTACT ON WENNER RESISTIVITY SOUNDINGS*     

RAKESH KUMAR  M. V. RAMANAIAH CHOWDARY 《Geophysical Prospecting》1977,25(3):471-480

The allowance for the influence of a vertical contact is evaluated on Wenner resistivity sounding curves, which are graphically constructed on bilogarithmic paper over simple composite earth models consisting of a vertical contact separating two- or three layered earth on one side and a homogeneous medium on the other side. The error incurred in the graphical constructions is explored. Finally, the use of these graphically constructed sounding curves is shown in the interpretation of two Wenner field soundings measured in a complex geologic area.  相似文献   

Secondary Silicates as a Barrier to Carbon Capture and Storage in Deccan Basalt     

Amit KUMAR  J.P. SHRIVASTAVA 《《地质学报》英文版》2020,94(3):861-876

Investigating the immobilization of CO2, previous basalt-water-CO2 interaction studies revealed the formation of carbonates over a short period, but with the extensive formation of secondary silicates (SS). The mechanisms involved in these processes remain unresolved, so the present study was undertaken to understand secondary mineral formation mechanisms. XRPD and Rietveld refinement data for neo-formed minerals show a drastic decrease in the Ca-O bond length, with the calcite structure degenerating after 80 h (hours). However, SEM images and EDS data revealed that a longer interaction time resulted in the formation of chlorite and smectite, adjacent to basalt grains which prevent basalt-water-CO2 interaction to form carbonates, thus restricting carbonate formation. As a result of this, the CO2 mineralization rate is initially high (till 80 h), but it later reduces drastically. It is evident that, for such temperature-controlled transformations, low temperature is conducive to minimizing SS surface coating at the time of mineral carbonation.  相似文献   

DIRECT INTERPRETATION OF TWO-ELECTRODE RESISTIVITY SOUNDINGS *     

RAKESH KUMAR 《Geophysical Prospecting》1974,22(2):224-237

This paper describes the procedure for interpreting the apparent resistivity data measured with the two-electrode array directly with the help of kernel function. The calculation of kernel function from the observed resistivity curve is done by the method of decomposition. In the method of decomposition the resistivity curve is approximated by a sum of certain functions, whose choice is only restricted by the requirement that the contribution to the kernel function corresponding to them should be easily computable. A few such functions are classified. These, and the standard curves for corresponding kernel functions obtained by utilising an integral expression for two-electrode array expressing the kernel explicitly in terms of the apparent resistivity functions, are plotted on log-log scale. The determination of layer parameters, that is, the layer resistivities and thicknesses from the kernel function can be carried out by a method proposed by Pekeris (1940).  相似文献   

Inlet sequence: a vertical succession of sedimentary structures and textures created by the lateral migration of tidal inlets   总被引：2，自引：0，他引：2  

NARESH KUMAR  JOHN E. SANDERS 《Sedimentology》1974,21(4):491-532

Tidal inlets, narrow, comparatively deep gaps between barrier islands, are channels through which tidal currents flow vigorously as the water enters and leaves the backbarrier lagoons, bays, and intertidal flats and marshes. Many geologists have compared tidal inlets to river channels and have speculated that if an inlet shifts laterally, it should deposit a distinctive sequence of sediments, analogous to the point-bar sequence left by a meandering stream channel. Fire Island Inlet, located 56 km east of New York City, has migrated WSW at a mean rate of 64 m/year during the period 1825–1940. Waves approaching the coast, predominantly from the southeast, have shifted sediment along the shore toward the WSW. Deposition of sediment on the east side of the inlet has forced the tidal currents to erode the west side of the inlet, thus causing lateral migration. Because hydraulic conditions vary from the channel floor to the subaerial part of the spit which is present on the ENE side of the channel, sedimentary structures and textures vary systematically with depth. We have determined the various sedimentary environments associated with the modern Fire Island Inlet, sampled and described the sediments from these environments, and have collected samples from corings made on that part of Fire Island through which the inlet has migrated. On the basis of our studies, we propose an inlet sequence which is formed by the lateral migration of a tidal inlet. The sequence includes five major units, as follows on p. 492. The sediments belonging to various units in this sequence have been identified in four borings made on those parts of Fire Island through which the Fire Island Inlet has migrated since 1825. This sequence should be applicable to other inlets also. We think that the boundary between deep channel and shallow channel units remains relatively fixed at ?4.5 m, whereas the thickness of the deep channel unit is determined by the depth range between ?4.5 m and the total depth of the inlet. Hence, the main source of variation in the inlet sequence will be the thickness of the deep-channel unit. Most of the sediments of the inlet sequence are incised below mean low water; hence they will almost certainly be preserved in the geologic record, even if all other associated sediments from barrier environments located above mean low water are not preserved. Because of the great variability possible in rates of lateral migration of inlets along the shore compared with the rates of barrier displacement perpendicular to the shore, inlet sediments may be preserved as elongate lenses, or as widespread blankets. The shape of inlet deposits reveals much about the behaviour of barriers during a submergence. Hence, inlet sediments should shed new light on sediments of the continental shelves and on basal transgressive sands in the geologic record.   相似文献   

THE BLIND-ZONE PROBLEM IN MULTIPLE REFRACTION-LAYER OVERBURDEN SITUATIONS*     

M. S. VIJAYA RAGHAVA  G. NANDA KUMAR 《Geophysical Prospecting》1979,27(2):474-479

The blind zone problem is examined with a view to provide a simple means of solving the problem in the general case of arbitrary number of refraction layers constituting the overburden to the masked layers. Considering the first arrival refraction interval corresponding to the masked layer which reduces to zero under blind zone conditions, a method to solve the problem is presented. Derivation of the critical distance expression is also included and convenient solutions to compute the thicknesses of the blind zone and its immediate overlayer are worked out. Based on test calculations on some known instances, the efficacy of the method is illustrated. A Fortran program for use when large numbers of refraction layers are involved under the overburden or when more than one masked layer is encountered is available from the authors.  相似文献   

Relict magnesian calcite oolite and subsidence of the Amazon shelf     

NARESH KUMAR  JOHN E. DAMUTH  MARCUS A. GORINI 《Sedimentology》1977,24(1):143-148

  相似文献   

Near shore waves,long-shore currents and sediment transport along micro-tidal beaches,central west coast of India     

Sajiv Philip CHEMPALAYIL  V Sanil KUMAR  G Udhaba DORA  Glejin JOHNSON 《国际泥沙研究》2014,29(3):402-413

Coastlines are undergoing constant geomorphologic changes with respect to the incident wave climate.Based on waves measured at 9 m water depth,simulation of near shore wave transformation is done using REFDIF-1numerical model and the near shore breaker parameters are estimated at two micro-tidal beaches along central west coast of India.Model results are validated with measured values.From the breaker parameters,long-shore current and long-shore sediment transport rates（LSTR） are computed by using semi-empirical equations.Estimated long-shore current and LSTR are showing dramatic variations with respect to seasons.Predominant direction of LSTR is observed towards north since the approach waves are from south-west direction during pre-monsoon and post monsoon.During monsoon season,waves are from west south-west and resulted in southerly transport.The estimated annual net and gross LSTR by Cambridge Environmental Research Consultants（CERC） at two locations are in the same order whereas LSTR estimated by Walton ＆ Bruno and Kamphuis equations are showing different estimations because of difference in surf-zone width and foreshore slope between the two locations.For micro-tidal beaches with length less than 6 km,Kamphuis equation is giving agreeable estimation of LSTR.Sensitivity analysis of LSTR estimate shows that coastal inclination is the prominent factor in determining LSTR than incident wave angle.  相似文献   

Tectonochemistry and p-t Conditions of Ramgarh and Almora Gneisses from Askot Klippe,Kumaun Lesser Himalaya     

Biraja P. DAS  Mallickarjun JOSHI  Ashutosh KUMAR 《《地质学报》英文版》2019,93(2):322-343

The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at 776°C temperature and 6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.  相似文献   

Palaeodiet of Miocene Producers and Depositional Environments: Inferences from the First Evidence of Microcoprolites from India     

Vivesh V. KAPUR  Kamlesh KUMAR  P. MORTHEKAI  Amritpal Singh CHADDHA 《《地质学报》英文版》2020,94(5):1574-1590

This paper reviews research on coprolites from India, providing the first evidence of microcoprolites from the early Miocene (Aquitanian) Khari Nadi Formation sedimentary succession, exposed about 1.5 km northeast of the village of Kotada, Kachchh (Kutch) District, Gujarat State, western India. Morphometric and size comparisons (in a statistical framework) with known coprolites from the Mesozoic-Cenozoic successions of India (including those recorded herein) and globally suggest that fishes were the likely producers of the Kotada coprolites. Scanning electron microscopy confirms the presence of fish dental remains within the coprolites, while both Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) reveal the phosphatic nature of the microscopic coprolite specimens (recorded herein) hinting that the producer(s) were predominantly carnivorous (ichthyophagous) in their diet. Furthermore, X-Ray Fluorescence (XRF) analysis of the host and associated lithologies allows us to deduce that the Kotada coprolites were deposited in a shallow marine environment, with possible aerial exposure of the host lithology occurring at some point after deposition. To the best of our knowledge, the present report is the first record of microscopic fish coprolites from India, as well as being the first from the Aquitanian of India and the oldest Neogene record from India.  相似文献