Palynological evidence for the Palaeocene evolution of the forearc basin, Indus Suture Zone, Ladakh, India     

Rajeev Upadhyay  Ram-Awatar  R. K. Kar  Anshu K. Sinha 《地学学报》2004,16(4):216-225

The discovery of Permian, Mesozoic and Palaeocene palynomorphs from the Nindam forearc basin, exposed along the Indus Suture Zone in Ladakh, is reported. The palynomorphs are from volcanogenic sandstones and are poorly preserved, distorted and show the effects of abrasion (striation marks). The frequent occurrence of Proxapertites indicates the assemblage is at least Palaeocene in age. The Palaeocene palynomorphs and sediments were transported to the Nindam trough from nearby elevated landward regions (islands). These Palaeocene provenance areas were characterized by an estuarine, nearshore, tropical, warm‐humid environment and were situated at equatorial palaeolatitudes. However, the occurrence of Permian and Mesozoic palynomorphs in the assemblage indicates that the Late Palaeozoic and Mesozoic Tethyan sedimentary rocks exposed along the northern margin of the Indian plate were redeposited into the tectonically active Cretaceous–Palaeocene trench–subduction complex that existed between the Indian and the Asian plates until the collision took place at ～50–60 Ma.  相似文献   

Reply to comments on 'Palynological evidence for the Palaeocene evolution of the forearc basin, Indus Suture Zone, Ladakh, India' by Peter Clift     

Rajeev Upadhyay 《地学学报》2005,17(2):200-201

  相似文献   

Thermal decomposition pattern and particle size estimation of iron minerals associated with the Cretaceous‐Tertiary boundary at Gubbio     

H. C. Verma  C. Upadhyay  A. Tripathi  R. P. Tripathi  N. Bhandari 《Meteoritics & planetary science》2002,37(7):901-909

Abstract— Mössbauer studies of the samples from the Cretaceous‐Tertiary (K‐T) boundary layer at Gubbio, Italy show that iron appears mainly in two phases, magnetically ordered hematite and a paramagnetic silicate phase. The average particle size of hematite is estimated to be in the range of 16 to 27 nm from transmission electron micrographs and lack of a Morin transition. The hyperfine magnetic field at the iron nucleus is observed to be somewhat less than that of bulk hematite, which may be explained by collective magnetic excitation. Stepwise heating up to 1000°C shows a decomposition pattern of the paramagnetic phase, which suggests it to be a tri‐octahedral layer silicate. The iron‐bearing phases found in the bulk sedimentary K‐T boundary material are different from those found in the spherules separated from this material indicating that the redox conditions changed rapidly after the impact, becoming more oxidizing during the period these bulk phases were formed.  相似文献   

Weak MHD discontinuities in a radiation-induced flow field     

Rishi Ram  Arisudan Rai  R. P. Upadhyay 《Astrophysics and Space Science》1984,102(2):277-286

The growth of weak MHD discontinuities have been studied in a radiation induced flow field at very high temperature. Growth and decay properties of weak MHD discontinuities have been discussed under the influences of time-dependent gasdynamic field, the radiation field and the magnetic field with finite electrical conductivity. The effects of thermal radiation and conduction of the global behaviour of weak MHD discontinuities have been studied under a quasi-equilibrium and quasi-isotropic hypothesis of the differential approximation to the radiative heat transfer equation. It is shown that the existence of the time-dependent radiation field gives rise to a radiation induced wave which has a negligibly small effect on the non-relativistic flow properties of the gasdynamic field. It is also shown that the radiation stresses resist the steepening tendency of a compressive weak wave and help in stabilizing it whereas the thermal conduction effects counteracts to destabilize it. It is found that under radiation effects the shock formation is either disallowed or delayed. The two cases of diverging waves and converging waves have been studied separately to answer a particular question as to when a shock discontinuity or a coustic will be formed or disallowed under curvature effects.  相似文献   

Love wave propagation in anisotropic inhomogeneous medium: Elastic parameters for equivalent isotropic case     

S. K. Upadhyay 《Pure and Applied Geophysics》1970,81(1):45-50

Summary It is shown that the problem of Love wave propagation in an anisotropic inhomogeneous medium can be studied alternatively by defining elastic parameters in the equivalent isotropic case. An example is considered to illustrate the application of the method in obtaining the frequency equation of Love waves, propagating in an anisotropic inhomogeneous layer embedded between two isotropic homogeneous half spaces.  相似文献   

Love wave dispersion: Errors due to assumption of isotropy     

Janardan G. Negi  S. K. Upadhyay 《Pure and Applied Geophysics》1970,80(1):102-107

Summary Frequency equation for Love waves, propagating in a transversely isotropic homogeneous layer which is embedded between two isotropic homogeneous half spaces, is obtained. Errors, in rigidity (h), density and thickness of the anisotropic layer, which arise due to the assumption of isotropy of the medium are calculated by numerically analyzing the frequency equation. The results show that the errors increase with the increasing frequencies, and their signs depend upon the value (whether less than or greater than 1) of the anisotropy co-efficient of the medium of the layer.  相似文献   

Love wave propagation in multilayered anisotropic inhomogeneous media     

S. K. Upadhyay 《Pure and Applied Geophysics》1970,81(1):51-63

Summary Love wave propagation in a finite set of anisotropic inhomogeneous layers lying between two anisotropic homogeneous half spaces is considered. Generalized frequency equation is obtained by using the Thomson-Haskell matrix method. The usefulness of the general analytical result for discussing more special cases of interest in seismology is brought out in the end.  相似文献   

Source parameters of earthquakes in northeast India from spectra of Rayleigh waves     

S.K. Upadhyay  V.K. Ahuja 《Tectonophysics》1981,75(3-4)

  相似文献   

Sorption Model for Dissolved Aluminium in Freshwaters     

S. Upadhyay  P. S. Liss  T. D. Jickells 《Aquatic Geochemistry》2002,8(4):255-275

A series of aluminium speciation measurements were madein the freshwaters of the Yare and Great Ouse rivers (England). Samples were analysedfor dissolved and particulate Al, suspended particulate matter (SPM), and other alliedchemical species in order to assess the role of sorption processes on the suspended phasesin controlling dissolved Al levels. Partitioning of Al occurs between solid andsolution phases with a distribution coefficient (K_d) which varies over about one anda half orders of magnitude for suspended particle concentrations of comparablemagnitude. A sorption model is proposed for dissolved Al concentrations in thesefreshwaters with most of the data fitting the model defined by a zone with K_dvalues of 0.316 × 10⁶ and 10⁷. However, a few data points lie outside thiszone, suggesting that other processes may also influence dissolved Al distributions.Nevertheless, the model may serve as a starting point for predicting concentrations ofdissolved Al in rivers where SPM levels are moderate to high (>1 mg l^-1 but< 75 mg l^-1), and indeed, this model works reasonably well for the Conway system(Wales). Further, the empirical distribution coefficient, K_d, decreases withincreasing suspended particle concentration, which may be due in part to colloidal phenomena.  相似文献   

Apparent resistivity over a three layer earth with anisotropic interstratum     

S. K. Upadhyay  Sri Niwas 《Pure and Applied Geophysics》1971,87(1):155-160

Summary The present work aims at investigating the effects of anisotropy on the apparent resistivity measurements over the surface of a three layer Earth. An appropriate model with the anisotropic layer embedded between two isotropic media is chosen for study. The point current source is assumed to be present at the surface of such a model. After writing the values of the potentials in each layer, expressions for apparent resistivities for Wenner and Schlumberger configurations are derived. Also, the expressions for potential for the limiting cases in which the bottom layer is infinitely resistive or infinitely conducting are derived. It is shown that these expressions can be recast into simpler forms corresponding to isotropic layer (s) on an isotropic half-space.  相似文献