Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal   总被引：1，自引：0，他引：1  

T. P. Ojha  R. F. Butler  P. G. DeCelles  J. Quade 《Basin Research》2009,21(1):61-90

The early Miocene Dumri Formation and middle Miocene–Pliocene Siwalik Group were deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold‐thrust belt. We report magnetostratigraphic data from four sections of these rocks in Nepal. Three of these sections are in the Siwalik Group in the hanging wall of the Main Frontal thrust, and one section is from the Dumri Formation in the hanging wall of the Main Boundary thrust (MBT). Thermal demagnetization experiments demonstrate that laminated siltstones yield palaeomagnetic data useful for tectonic and magnetostratigraphic studies whereas other lithofacies yield data of questionable reliability. Magnetostratigraphic data have been acquired from 297 sites within a 4200‐m‐thick section of Siwalik deposits at Surai Khola. The observed sequence of polarity zones correlates with the geomagnetic polarity time scale (GPTS) from chron C5Ar.1n to chron C2r.2n, spanning the time frame ca. 12.5–2.0 Ma. At Muksar Khola (eastern Nepal), 111 palaeomagnetic sites from a 2600‐m‐thick section of the Siwalik Group define a polarity zonation that correlates with the GPTS from chron C4Ar.2n to chron C2Br.1r, indicating an age range of ca. 10.0–3.5 Ma. At Tinau Khola, 121 sites from a 1824‐m‐thick section of the Siwalik Group are correlated to chrons C5An.1n through C4r.1n, equivalent to the time span ca. 11.8–8.1 Ma. At Swat Khola, 68 sites within a 1200‐m‐thick section of lower Miocene Dumri Formation are correlated with chrons C6n through C5Bn.2n, covering the time span ca. 19.9–15.1 Ma. Together with previous results from Khutia Khola and Bakiya Khola, these data provide the first magnetostratigraphic correlation along nearly the entire NW–SE length of Nepal. The correlation demonstrates that major lithostratigraphic boundaries in the Siwalik Group are highly diachronous, with roughly 2 Myr of variability. In turn, this suggests that the major sedimentological changes commonly inferred to reflect strengthening of the Asian monsoon are not isochronous. Sediment accumulation curves exhibit a 30–50% increase in accumulation rate in four of the five sections of the Siwalik Group, but the timing of this increase ranges systematically from ～11.1 Ma in western Nepal to ～5.3 Ma in eastern Nepal. If this increase in sediment accumulation rate is interpreted as a result of more rapid subsidence owing to thrust loading in the Himalaya, then the diachroneity of this increase suggests lateral propagation of a major thrust system, perhaps the MBT, at a rate of ca. 103 mm year^?1 across the length of Nepal.  相似文献   

Stellar sources in the isogal inner galactic bulge field (l=0°,b= − 1°)     

D. K. Ojha  A. Omont  S. Ganesh  G. Simon  M. Schultheis 《Journal of Astrophysics and Astronomy》2000,21(1-2):77-90

ISOGAL is a survey at 7 and 15 μm with ISOCAM of the inner galactic disk and bulge of our Galaxy. The survey covers ∼ 22 deg² in selected areas of the centrall = ±30 degree of the inner Galaxy. In this paper, we report the study of a small ISOGAL field in the inner galactic bulge (l = 0°,b = −1°, area = 0.033deg²). Using the multicolor nearinfrared data (IJK_s) of DENIS (DEep Near Infrared Southern Sky Survey) and mid-infrared ISOGAL data, we discuss the nature of the ISOGAL sources. The various color-color and color-magnitude diagrams are discussed in the paper. While most of the detected sources are red giants (RGB tip stars), a few of them show an excess in J-K_s and K_s-[15] colors with respect to the red giant sequence. Most of them are probably AGB stars with large mass-loss rates.  相似文献   

Stellar contents and star formation in the young open cluster Stock 8     

Jessy Jose  A. K. Pandey  D. K. Ojha  K. Ogura  W. P. Chen  B. C. Bhatt  S. K. Ghosh  H. Mito  G. Maheswar  Saurabh Sharma 《Monthly notices of the Royal Astronomical Society》2008,384(4):1675-1700

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Interstellar Medium and Star Formation Studies with the Square Kilometre Array     

P. Manoj  S. Vig  G. Maheswar  U. S. Kamath  A. Tej 《Journal of Astrophysics and Astronomy》2016,37(4):38

Stars and planetary systems are formed out of molecular clouds in the interstellar medium. Although the sequence of steps involved in star formation are generally known, a comprehensive theory which describes the details of the processes that drive formation of stars is still missing. The Square Kilometre Array (SKA), with its unprecedented sensitivity and angular resolution, will play a major role in filling these gaps in our understanding. In this article, we present a few science cases that the Indian star formation community is interested in pursuing with SKA, which include investigation of AU-sized structures in the neutral ISM, the origin of thermal and non-thermal radio jets from protostars and the accretion history of protostars, and formation of massive stars and their effect on the surrounding medium.  相似文献   

High mass-loss asymptotic giant branch stars detected by the Midcourse Space Experiment in the 'intermediate' and 'outer' Galactic bulge     

D. K. Ojha  A. Tej  M. Schultheis  A. Omont  F. Schuller 《Monthly notices of the Royal Astronomical Society》2007,381(3):1219-1234

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Non‐point source pollution estimation using a modified approach     

Ramakar Jha  C. S. P. Ojha  K. K. S. Bhatia 《水文研究》2007,21(8):1098-1105

Non‐point source (NPS) pollution from agricultural land is increasing exponentially in many countries of the world, including India. A modified approach based on the conservation of mass and reaction kinetics has been derived to estimate the inflow of non‐point source pollutants from a river reach. Two water quality variables, namely, nitrate (NO₃) and ortho‐phosphate (o‐PO₄), which are main contributors as non‐point source pollution, were monitored at four locations of River Kali, western Uttar Pradesh, India, and used for calibration and validation of the model. Extensive water quality sampling was done with a total of 576 field data sets collected during the period from March 1999 to February 2000. Remote sensing and geographical information system (GIS) techniques were used to obtain land use/land cover of the region, digital elevation model (DEM), delineation of basin area contributing to non‐point source pollution at each sampling location and drainage map. The results obtained from a modified approach were compared with the existing mass‐balance equations and distributed modelling, and the performances of different equations were evaluated using error estimation viz. standard error, normal mean error, mean multiplicative error and correlation statistics. The developed model for the River Kali minimizes error estimates and improves correlation between observed and computed NPS loads. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Self-similar flow behind a spherical shock with varying strength in an inhomogeneous self-gravitating medium     

S. N. Ojha  Onkar Nath 《Astrophysics and Space Science》1987,129(1):11-17

The self-similar model of a shock wave, produced on account of an instantaneous release of energy in an inhomogeneous self-gravitating gaseous mass, has been discussed with the help of equations of motion and equilibrium conditions. The disturbances are headed by a shock of variable strength. The variation of velocity density, pressure, and mass have been discussed for the different values of strength of the shock.  相似文献   

Spectrophotometry of Comet Bradfield (1987s)     

D. K. Ojha  S. C. Joshi 《Earth, Moon, and Planets》1989,44(1):1-5

Spectral scans of Comet Bradfield (1987s) at heliocentric distance of 1.539 AU have been observed spectrophotometrically. The column densities and production rates of C₂ and CN have been derived.  相似文献   

Colour indices of the Markarian galaxies     

D. K. Ojha  S. C. Joshi 《Astrophysics and Space Science》1991,183(2):245-257

By use of the ANS ultraviolet fluxes, optical (UBV) and IRAS infrared fluxes, several colour indices for a few Markarian galaxies have been investigated. A comparison of these indices with those for normal NGC galaxies has been carried out. Similarities and differences in the indices for the two groups of galaxies have been discussed and possible causes have been indicated.  相似文献   

Finite volume model for reactive transport in fractured porous media with distance- and time-dependent dispersion     

Pramod Kumar Sharma  C.S.P. Ojha  Nitin Joshi 《水文科学杂志》2013,58(8):1582-1592

Abstract

There are very few studies of fractured porous media that use distance- and time-dependent dispersion models, and, to the best of our knowledge, none which compare these with constant dispersion models. Therefore, in this study, the behaviour of temporal and spatial concentration profiles with distance- and time-dependent dispersion models is investigated. A hybrid finite volume method is used to solve the governing equations for these dispersion models. The developed numerical model is used to study the effects of matrix diffusion coefficient, groundwater velocity and matrix and fracture retardation factor on concentration profiles in the application of constant, distance-dependent and time-dependent dispersion models. In addition, an attempt is made to evaluate the applicability of these dispersion models by using the models to simulate experimental data. It was found that a better fit to the observed data is obtained in the case of distance- and time-dependent dispersion models as compared to the constant dispersion model. Thus, these numerical experiments indicate that distance- and time-dependent dispersion models have better simulation potential than the constant dispersion model.  相似文献