Hydrocarbon Potential of Deeply Buried Reservoirs in the Astrakhan Oil and Gas Accumulation Zone: Problems and Solutions

Geotectonics - Global experience in oil exploration and the discovery of the Tupi field in Brazil and the Tiber field in the Gulf of Mexico in the last decade have confirmed the existence of giant...     

Foraminifers in the global stratotype (GSSP) of the Permian-Triassic boundary (Bed 27, Meishan,South China)

The paper documents the results of a detailed study of the taxonomic composition and stratigraphic distribution of foraminifers in the Permian-Triassic transition bed (Bed 27) in the P-T GSSP (Bed 27, Meishan, South China). The earliest foraminiferal assemblage that followed the largest biotic crisis at the end of the Permian includes 15 genera of four orders, of which lagenids were the most abundant and diverse. The order Lagenida includes the following families: Pachyphloiidae (Pachyphloia), Geinitzinidae (Lunucammina s.l. (= Geinitzina = Neogeinitzina) and Robuloididae (Robuloides). In addition, the assemblage includes numerous members of the family Ichthyolariidae, the generic assignment of which needs confirmation: Frondinodosaria, Nodosinelloides, Protonodosaria, Tauridia, and Eocristellaria. Most recorded taxa occur in both Permian and Lower-Middle Triassic beds in the Tethyan Region and outside it, mainly in the middle, less commonly in the higher latitudes of the Northern and Southern Hemispheres. Apart from lagenids, a small proportion in the assemblages is represented by taxa of wide stratigraphic and geographical ranges (cosmopolitans) of the order Ammodiscida (Ammodiscus, Glomospiranella), and the order Globivalvulida (Globivalvulina), order Cornuspirida, family Neodiscidae (Neodiscus), family Hemigordiidae (Hemigordius, Hemigordiella) and a genus of uncertain affinity (Abriolina), typical of the Permian in the Tethyan Realm. The new results confirm previous records of foraminifers of the genera Lunucammina s.l., Pachyphloia, Robuloides, Nodosinelloides, Cryptoseptida, Globivalvulina, Hemigordius, and Ammodiscus in the P-T boundary bed in the Meishan section, and supplement the list of recorded taxa by Neodiscus, Abriolina, Eocristellaria, Tauridia, and Hemigordiellina. New results update the data on the diversity and abundance of foraminiferal shells in the sections as well as reveal some problems of their identifications. No significant biological innovations, changes in variability, or appearance of new taxa are registered immediately above the critical level at the P-T boundary, while the extinction of some survivors continued after the crisis.     

Cosmic particles (micrometeorites) and nanospheres from the Cretaceous-Paleogene (K/T) boundary clay layer at the Stevns Klint Section,Denmark

This paper presents new data on numerous small metallic particles of iron, copper, Fe-Ni, Fe-Ni-Co, and Fe-Cr alloys, magnetite, and aluminosilicate balls of cosmic origin found in the black clay boundary layer between the Cretaceous and Paleogene in the Stevns Klint Section (Denmark). The findings imply that a fall of an asteroid to Earth 65 Ma ago was accompanied with falling of finely dispersed metallic particles of extraterrestrial nature related to the asteroid fragments or to micrometeorites following the asteroid or to the intense supply of cosmic dust. The huge amount of finely dispersed matter that fell to Earth at that time should be considered in further reconstructions of events at the boundary of the Cretaceous and Paleogene.     

The Paleoproterozoic Fedorov–Pana Layered PGE complex of the northeastern Baltic Shield,Arctic Region: New U–Pb (baddeleyite) and Sm–Nd (sulfide) data

For the first time zircons have been extracted from gabbro–norite of a lower layered horizon of the West Pana Massif in the Pt–Pd Kievei deposit of the Fedorov–Pana Layered Complex. Those zircons have been used for U–Pb dating along with Sm–Nd age determination on sulfide minerals. The obtained new isotopic data are a U–Pb zircon age of 2500 ± 4 Ma, while the Sm–Nd (mineral and whole-rock) isochron yielded 2483 ± 86 Ma. These results correspond to the first phase of the Pt–Pd reef complex formation in the Layered Complex. The Pt–Pd reef formation has been dated by U–Pb baddeleyite and zircon analyses in the East Pana Massif to 2464 ± 12 Ma. The 2485–2464 Ma time span corresponds to the second phase of the Pt–Pd reef formation in the Fedorov–Pana ore cluster.     

Probabilistic Regularities in Unfavorable Hydrochemical Phenomena

The balance equation for a substance washed out in a river basin is analyzed under the assumption that the runoff of this substance and its reserves in the watershed are directly proportional. The proportionality factor is perturbed by a random component, which accounts for the effect of atmospheric precipitation. The balance equation is transformed into a stochastic differential equation with a multiplicative white noise, which is used to construct a Fokker-Plank equation for the probability density of chemical flow. A stationary solution containing a power function is found for this equation. Because of the proportionality of the concentration and chemical flow, the concentration distribution also obeys the power law. Statistical treatment of empirical data on some water quality characteristics and water flow showed that the power law adequately describes the probability of unfavorable hydrochemical events. The parameters of this law for turbidity, color index, permanganate oxidability, and ammonia concentration are evaluated.__________Translated from Vodnye Resursy, Vol. 32, No. 4, 2005, pp. 452–458.Original Russian Text Copyright © 2005 by Dolgonosov, Korchagin.     

Statistical assessment of relationships between water flow in a river and water turbidity in water intakes

Probability distributions of water flow and its turbidity after passing through water intake structures are considered. Heavy tails with a power distribution are shown to exist. These distributions are used to find the dependence between water turbidity at the inlet to the water station and water flow in the river. Quantiles of these distributions are estimated to characterize the levels of water flow and turbidity with a given exceedance probability.Translated from Vodnye Resursy, Vol. 32, No. 2, 2005, pp. 196–204.Original Russian Text Copyright © 2005 by Dolgonosov, Korchagin.     

Seasonal variations of the distribution of river water quality

The probability distributions of different values of water quality indices have been shown theoretically to follow a two-parameter lognormal law with season-dependent parameters. The obtained distribution law was checked against data of many-year water quality monitoring in the Moskva R. (at Rublevo Settl.). The distributions of several hydrochemical and microbiological indices have been studied. The seasonal dependence of parameters have been shown to cause the splitting of water quality index distributions predominantly into two lognormal branches, one corresponding to low-water seasons and the other corresponding to floods. Exceptions are water turbidity and color index: the former splits into three lognormal branches (corresponding to periods of winter low-water period, summer period with moderate rains, floods, and high rain floods), while the color index has only one branch, embracing all seasons.     

Surface perturbations generated by a stratified flow of finite depth over obstacles

We studied the structure of the surface perturbations generated by a stratified flow of an ideal fluid of finite depth around underwater obstacles. We consider a cylinder modeled by a point dipole localized near the density interface both above and below the interface. It is shown that density jumps characteristic of the marine medium significantly influence the formation and variability of the structure of the surface perturbations generated during a fluid??s flowing around an underwater obstacle. The results are compared with the data of the previous model calculations made by the authors for an infinite flow around an obstacle [4]. Significant differences between them are revealed, which should be taken into account in the solution of practical problems, for example, monitoring of coastal marine basins.