Trace fossils from the late cretaceous Lameta Formation,Jabalpur area,Madhya Pradesh: Paleoenvironmental implications     

Omnath Saha  U. K. Shukla  Rekha Rani 《Journal of the Geological Society of India》2010,76(6):607-620

In Jabalpur area about 18 m to 45 m thick Lameta Formation is stratigraphically divisible into five lithounits namely, Green Sandstone, Lower Limestone, Mottled Nodular Beds, Upper Limestone and Upper Sandstone. Having differentiated lithofacies constitution and here grouped as facies associations, these units are intensively burrowed and sparingly fossiliferous. Ichnogenera including Arenicolites, Calycraterion, Fucusopsis, Laevicyclus, Macanopsis, Ophiomorpha, Paleomeandron, Rhizocorallium, Stipsellus, Thalassinoides and Zoophycos are recovered from the Lower Limestone, Mottled Nodular Beds and Upper Limestone associations of the Lameta Formation of Jabalpur area.Among these, Arenicolites, Calycraterion, Laevicyclus, Ophiomorpha, Rhizocorallium, Stipsellus and Thalassinoides belong to mixed Skolithos and Cruziana ichnofacies and indicate sandy backshore to sublittoral condition of deposition. Additionally rhyzocretes, some times chertified, are also present in different parts of the Lameta Formation. Ichnofacies assemblage supported by sedimentological information suggests that the Lameta Formation of Jabalpur area was deposited in coastal marine settings where sediments were subaerially exposed intermittently.  相似文献   

The response of the South Asian Summer Monsoon circulation to intensified irrigation in global climate model simulations     

Sonali P. Shukla  Michael J. Puma  Benjamin I. Cook 《Climate Dynamics》2014,42(1-2):21-36

Agricultural intensification in South Asia has resulted in the expansion and intensification of surface irrigation over the twentieth century. The resulting changes to the surface energy balance could affect the temperature contrasts between the South Asian land surface and the equatorial Indian Ocean, potentially altering the South Asian Summer Monsoon (SASM) circulation. Prior studies have noted apparent declines in the monsoon intensity over the twentieth century and have focused on how altered surface energy balances impact the SASM rainfall distribution. Here, we use the coupled Goddard Institute for Space Studies ModelE-R general circulation model to investigate the impact of intensifying irrigation on the large-scale SASM circulation over the twentieth century, including how the effect of irrigation compares to the impact of increasing greenhouse gas (GHG) forcing. We force our simulations with time-varying, historical estimates of irrigation, both alone and with twentieth century GHGs and other forcings. In the irrigation only experiment, irrigation rates correlate strongly with lower and upper level temperature contrasts between the Indian sub-continent and the Indian Ocean (Pearson’s r = ?0.66 and r = ?0.46, respectively), important quantities that control the strength of the SASM circulation. When GHG forcing is included, these correlations strengthen: r = ?0.72 and r = ?0.47 for lower and upper level temperature contrasts, respectively. Under irrigated conditions, the mean SASM intensity in the model decreases only slightly and insignificantly. However, in the simulation with irrigation and GHG forcing, inter-annual variability of the SASM circulation decreases by ~40 %, consistent with trends in the reanalysis products. This suggests that the inclusion of irrigation may be necessary to accurately simulate the historical trends and variability of the SASM system over the last 50 years. These findings suggest that intensifying irrigation, in concert with increased GHG forcing, is capable of reducing the variability of the simulated SASM circulation and altering the regional moisture transport by limiting the surface warming and reducing land–sea temperature gradients.  相似文献   

Spatio-temporal dynamics of heavy metals in sediments of the river estuarine system: Mahanadi basin (India)   总被引：1，自引：1，他引：0  

Sanjay Kumar Sundaray  Binod Bihari Nayak  Byeong-Gweon Lee  Dinabandhu Bhatta 《Environmental Earth Sciences》2014,71(4):1893-1909

Dynamics of heavy metals in the surface sediments of Mahanadi river estuarine system were studied for three different seasons. This study demonstrates that the relative abundance of these metals follows in the order of Fe > Mn > Zn > Pb > Cr > Ni ≥ Co > Cu > Cd. The spatial pattern of heavy metals supported by enrichment ratio data, suggests their anthropogenic sources possibly from various industrial wastes and municipal wastes as well as agricultural runoff. The metal concentrations in estuarine sediments are relatively higher than in the river due to adsorption/accumulation of metals on sediments during saline mixing, while there is a decreasing trend of heavy metal concentrations towards the marine side. The temporal variations for metals, such as Fe, Mn, Zn, Ni and Pb exhibit higher values during monsoon season, which are related to agricultural runoff. Higher elemental concentrations are observed during pre-monsoon season for these above metals (except Ni) at the polluted stations and for metals, such as Cr, Co and Cd at all sites, which demonstrate the intensity of anthropogenic contribution. R-mode factor analysis reveals that “Fe–Mn oxy hydroxide”, “organic matter”, “CaCO₃”, and “textural variables” factors are the major controlling geochemical factors for the enrichment of heavy metals in river estuarine sediment and their seasonal variations, though their intensities were different for different seasons. The relationships among the stations are highlighted by cluster analysis, represented in dendrograms to categorize different contributing sites for the enrichment of heavy metals in the river estuarine system.  相似文献   

Shell microstructure of late Cretaceous (Maastrichtian) oysters from Ariyalur,Tamil Nadu     

Anand K. Jaitly  Sanjay K. Mishra  Shrinjana Sen 《Journal of the Geological Society of India》2014,84(1):41-54

The micro-morphological shell characters (both in optical microscope and SEM) have been used to discriminate in between oyster’s sub-families Pycnodonteinae Stenzel 1959, Exogyrinae Vyalov 1936, Ostreinae Refinesque 1815 and Lophinae Vyalov 1936. These sub-families are represented by six constituent genera Phygraea (Phygarea) vesicularis (Lamarck 1806), Hyotissa semiplana (Sowerby1813), Curvostrea rouvellei (Coquand 1862), Ceratostreon pliciferum (Dujardin 1837), Agerostrea ungulata (Schlotheim 1813) and Rastellum (Arctostrea) pectinatum (Lamarck 1810) in the late Cretaceous (Maastrichtian) sediments of the Ariyalur area of Tamil Nadu, south India. The optical microscopic observations and SEM studies of the shells of these six genera clearly indicate that all the four sub-families consist of distinctive set of shell-microstructures. Sub-family Pycnodonteinae is characterized by predominance of vesicular, exogyrinae by prismatic, Ostreinae by cross foliated and Lophinae by foliated shell microstructures. Besides their characteristic shell microstructures, some additional microstructures are also visible in the shells of some of the genera of these four sub-families.  相似文献   

Soil responses near Delhi ridge and adjacent regions in Greater Delhi during incidence of a local earthquake     

H. S. Mandal  P. K. Khan  A. K. Shukla 《Natural Hazards》2014,70(1):93-118

In this study, soil response was carried out for the Greater Delhi region. A folded Proterozoic formation was identified as Delhi ridge, passes through its central part along SSW–NNE direction, and appears to be a main geomorphic feature for the study area. The Delhi ridge is an exposed quartzite rock of about 10–100 m wide and ~25 km long with gentler dipping both toward east and west. We have considered the exposed part as an outcrop side near the ridge axis and the dipping area as rigid base away from the ridge axis for ground motion study during the occurrence of the 25 November 2007 earthquake with magnitude M _L 4.3 (Richter scale) that occurred at Delhi–Haryana State boundary. The degree of shaking was very strong and reported major cracks in the buildings near the epicenter area. We have studied the soil response parameters at the surface level, considering horizontally stratified soil layers above rigid base. The equivalent linear method was used for soil response analysis at 25 sites in Greater Delhi area. The peak amplification factors vary from 3.2 to 5.9 and peak resonance frequency varies from 1.2 to 5.3 Hz. The correlation among the peak amplification factor (A) and frequency (f) was empirically established as A = 0.36f + 3.60. Increasing peak amplification factor was found at sites with increasingly thicker alluvium deposit with lower frequency contains ground motion and vice versa. Seismic zoning map was also reconstructed for peak amplification factors and predominant periods for the study area for the mitigation purposes of earthquake damage. The average shear wave velocity up to 30 m soil depth is also obtained for site classification. The average velocity to 30 m [ $ \overline{{V_{\text{s}} }} (30) $ ] is a widely used parameter for classifying sites for predicting their potentiality to amplify seismic shaking. A lower value [ $ \overline{{V_{\text{s}} }} (30) $ ] thus yields a more conservative estimate of ground motion, which generally increases as $ \overline{{V_{\text{s}} }} (30) $ decreases. Present estimate of $ \overline{{V_{\text{s}} }} (30) $ varies from 315 to 419 m/s. In this study, we have identified two site classes C and D, as per National Earthquake Hazard Reduction Program. The city planner or engineers can directly use these data for site-specific assessment during retrofitting of the existing structure, demolition of the old buildings and design a new structure to avoid major destruction of the buildings due to future earthquake.  相似文献   

Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe     

Sanjay Sarkar 《Astrophysics and Space Science》2014,349(2):985-993

The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.  相似文献   

Fall,classification and cosmogenic records of the Sabrum (LL6) chondrite     

S. Ghosh  S. V. S. Murty  P. N. Shukla  A. D. Shukla  R. R. Mahajan  N. Bhandari  N. C. Pant  J. B. Ghosh  S. Shome 《Meteoritics & planetary science》2002,37(3):439-448

Abstract— The petrographic and chemical characteristics of a fresh Indian meteorite fall at Sabrum are described. Its mean mineral composition is defined by olivine (Fa_31.4), orthopyroxene (Fs_25.1,Wo_2.0), clinopyroxene (Wo₄₅En_45.6Fs_9.4) and plagioclase (An_10.6Ab_83.6Or_5.8). The meteorite shows moderate shock features, which indicate that it belongs to the S4 category. Based on mineralogical and chemical criteria the meteorite is classified as an LL6 brecciated veined chondrite. Several cosmogenic radioisotopes (⁴⁶Sc, ⁷Be, ⁵⁴Mn, ²²Na and ²⁶Al), noble gas (He, Ne, Ar, Kr and Xe), nitrogen isotopes, and particle tracks density have been measured. Concentrations of cosmogenic ²¹Ne and ³⁸Ar indicate that its cosmic‐ray exposure age is 24.8 Ma. Small amounts of trapped Kr and Xe, consistent with petrologic class 5/6, are present. The track density in olivines is found to be (1.3 ± 0.3) × 10⁶/cm². Activities of most of the short‐lived isotopes are lower than those expected from solar cycle variation. ²²Na/²⁶Al (1.12 ± 0.02) is found to be significantly anomalous, being ?25% lower than expected from the Climax neutron monitor data. These results indicate that the cosmic‐ray flux during the terminal segment of the meteoroid orbit was low. The activities of ²⁶Al and ⁶⁰Co and the track density indicate small meteoroid size with a radius ?15 cm.  相似文献   

Pancake cyclones and anti-cyclones in the ionosphere     

V. I. Petviashvili  O. A. Pokhotelov  P. K. Shukla  L. Stenflo 《Astrophysics and Space Science》1993,202(2):363-372

The formation of pancake cyclones and anticyclones in the E-region of the Earth's ionosphere is considered. It is shown that the vortices can be maintained by the neutral winds or by chemical reactions including the energy release caused by the triple collisions of atomic oxygen with neutrals. It is found that the variations of the magnetic fields induced by the vortices are not localized and decrease slowly far from the vortex core. They can be easily detected by ground based magnetometers or by facilities on board the low-orbiting satellites.  相似文献   

Electron surfing acceleration in oblique magnetic fields     

M. E. Dieckmann  B. Eliasson  M. Parviainen  P. K. Shukla  A. Ynnerman 《Monthly notices of the Royal Astronomical Society》2006,367(3):865-872

Initially, inhomogeneous plasma jets, ejected by active galactic nuclei and associated with gamma-ray bursts, are thermalized by the formation of internal shocks. Jet subpopulations can hereby collide at Lorentz factors of a few. As the resulting relativistic shock expands into the upstream plasma, a significant fraction of the upstream ions is reflected. These ions, together with downstream ions that leak through the shock, form relativistic beams of ions that outrun the shock. The thermalization of these beams via the two-stream instability is thought to contribute significantly to plasma heating and particle acceleration by the shock. Here, the capability of a two-stream instability to generate relativistic field-aligned and cross-field electron flow, is examined for a magnetized plasma by means of a particle-in-cell (PIC) simulation. The electrons interact with the developing quasi-electrostatic waves and oblique magnetic fields. The simulation results bring forward evidence that such waves, by their non-linear interactions with the plasma, produce a highly relativistic field-aligned electron flow and electron energies, which could contribute to the radio synchrotron emissions from astrophysical jets, to ultrarelativistic leptonic subpopulations propagating with the jet and to the halo particles surrounding the accretion disc of the black hole.  相似文献   

Characterization of Surface Geological Material in Northwest India and Adjoining Areas of Pakistan Using Normalized Difference Water Index,Land Surface Temperature and Silica Index     

Sanjay Das 《Journal of the Indian Society of Remote Sensing》2018,46(10):1645-1656

Land surface temperature (LST) shows negative correlation with the Normalized Difference Water Index (NDWI). Variability in the degree of correlation between LST and NDWI is ascribed to the physical character of specific geological material. Northwest India exhibits various landforms with different geological materials and has been broadly classified into four zones. Structural ridges of Aravalli Mountain of different rock compositions show strong variability both in NDWI (range 1.154, SD?=?0.0599) and in LST (range 24 °C and SD?=?2.54). Negative LST–NDWI correlation in this sector is partially linear. Western Thar Desert, having homogenous silica sand of lower emissivity shows least variability in its NDWI (range 0.88, SD?=?0.027) and moderate variability in its LST (20 °C, SD?=?2.389). Strong negative correlation of LST with NDWI is exhibited here. Band ratio Silica map in this sector shows strong positive correlation with LST. The eastern part of the Thar desert with mixed rocky knobs, and wind-blown sand shows low variability in NDWI (range 0.85) as well as LST (range 15 °C). Area in Indus–Bias–Sutlej River basin, dominated with fluvial sediments with lesser amount of windblown sediments, show low variability of NDWI (0.85) and moderate variability of LST (range 23 °C). In the areas, around Luni river higher NDWI trend is recorded, which is unrelated to present drainage trends indicating presence of palaeo-drainage. In addition, high NDWI and high LST bearing linear zones at places are interpreted as structural lineaments/faults based on pattern, moisture content and thermal high.  相似文献