The nature of the high values of the anisotropy of magnetic susceptibility of rock samples with polydomain ferromagnetics

Samples of different rocks, which possess high values of the anisotropy of magnetic susceptibility, were studied by the magneto-mineralogical and optical methods and by microprobe analysis. It was established that for the samples, which contain the pseudo-single-domain ferromagnetite elongated particles, the source of the anisotropy of magnetic susceptibility is the distribution anisotropy of not only ferromagnetic grains themselves, but also ferromagnetic patterns in the heterogeneous accessory minerals. For samples with multidomain ferromagnetic materials, the nature of the anisotropy of magnetic susceptibility is caused by the orientation of the ilmenite lamellar phase in the structures of disintegration of titanomagnetites or by the orientation of the ferromagnetic structures of disintegration in iron sulfides.     

Hydrocarbons in the Bay of Bengal and Central Indian Basin bottom sediments: indicators of geochemical processes in the lithosphere

A study on the bulk distributions and molecular structures of n-alkanes and polycyclic aromatic hydrocarbons (PAH) in organic matter of the sediments from the Bay of Bengal and the Eastern and Central Indian Basins was undertaken. The former two regions represent areas characterised by “normal” sedimentation while the third one mainly represents a region of “active tectonism”. Content of the hydrocarbons in the sediments of “normal” sedimentation ranges between 4.6 and 10.5 μg/g and aromatic hydrocarbons ranges between 0 and 0.38 μg/g. n-Alkanes in the sediments of the northern deep part of the Bay of Bengal consist mostly of long-chain structures (total C₂₅–C₃₃ up to 70%) with a high carbon preference index (CPI=3.01–3.43), indicating a large contribution of organic matter from terrigenous sources. The sediments from the Eastern Indian Basin have n-alkane distributions in which the long-chain components did not exceed 52.5% and the CPI was 1.7–1.90, indicating that the hydrocarbons are mostly derived from marine sources. Sharp increases of hydrocarbons are found in the vicinity of the tectonically active region of the Central Indian Basin, particularly in the sediments collected from the fracture zone. The total concentration of hydrocarbons increase to 170 μg/g and the aromatic hydrocarbons fraction to 156.3 μg/g. The proportion of short-chain n-alkanes increases up to 70%, CPI decreases to 0.76–1.12, and high concentrations of n-C₁₆ (16–40%) occur, all of which are absent in the other samples. The molecular content of PAH includes the unsubstituted individual structures: biphenyl, fluorene, pyrene, perylene, benzo(ghi)perylene, and the groups of homologues of naphthalene, benzofluorene, phenanthrene and chrysene. The association of the PAH and composition of paraffin hydrocarbons in the surficial sediments of deformation zone indicate that these are the resultant products of hydrothermal processes. It is, therefore, suggested that the association and composition of the hydrocarbons in sediments can be utilised as a paleoceanographic parameter to decipher the history of tectonism of an area.     

Strong increase of the linear polarization of RZ Psc at deep minimum

Institute of Astrophysics, Tadzhik Academy of Sciences. Translated from Astrofizika, Vol. 34, No. 3, pp. 333–343, May–June, 1991.     

The investigations of ‘zodiacal light’ of isolated AE-Herbig stars with non-periodic Algol-type minima

High linear polarization (up to 5–8%) discovered by our group in the deep minima of isolated AE-Herbig stars is discussed in the framework of the model of zodiacal light produced by scattering matter in a circumstellar dust envelope (probably in protoplanetary discs). The numerical simulations of polarizational and colourimetrical properties of the scattered light based on the Mie theory permit to obtain from the observations some important parameters of circumstellar dust: the size distribution of grains, their rough chemical composition (silicate/graphite), the flatness of the dust envelope.Moreover, the position angle of polarization in deep minima may be used for determination of the symmetry axis projection of circumstellar disc on the sky relative to the direction of local interstellar magnetic field. The latest is important in order to understand the role of the magnetic field at the initial phase of gravitational collapse of protostellar clouds.Finally, the component of linear polarization which is due to the alignment of nonspherical circumstellar grains may be separate from the observed polarization under certain conditions.Paper presented at the 12th European Regional Astronomical Meetings of the IAU European Astronomers Look to the Future, held 8–11 October, 1990 in Davos, Switzerland.     

Determination of threshold concentrations of metals in indicator algae of coastal waters in the northwest Sea of Japan

Background concentrations of Fe, Mn, Cu, Zn, Pb, Cd, and Ni were calculated for thalli of abundant algae of Fucus, Silvetia, Sargassum, Cystoseira spp. from the northwest Sea of Japan during 1987–2008. As the upper threshold levels of metal background concentrations, the median values plus double medians of absolute deviations from the medians were used (Me + 2MAD). The lower threshold level of the background concentration equal to the physiological need for an element is the median of 15% minimum values in the sampling minus the double median of absolute deviations from the median (Me₁₅–2MAD₁₅). The range of Me₁₅ ± 2MAD₁₅ is considered the natural background range of concentrations.     

Dynamics of Surging Glaciers in the Sugran River Basin (Pamirs)

Doklady Earth Sciences - The results of measurements of the area of surging glaciers in 1974 and 2018 are compared to the data on their areas in 1913. A large decadal (middle-term) variability in...     

Causes of Cretaceous Remagnetization on the Southwestern Periphery of the Archipelago of the New Siberian Islands

This study demonstrates rock-magnetic and paleomagnetic investigations of Devonian and Mesozoic deposits of Kotelny, Stolbovoy, and Great Lyakhovsky islands. The results indicate that local remagnetization took place on the southwestern periphery on the archipelago of the New Siberian Islands. A comparison of new data with the apparent polar wander path for Siberia shows that the remagnetization happened during collisional events between 140 and 80 Ma and affected only the marginal part of the terrane of the New Siberian Islands that was directly facing the deformation front. The consistent younging of the remagnetization age from the south to the north indicates dextral rotation of the terrane of the New Siberian Islands during its collision with Siberia.     

The proportional effect in gold-bearing quartz veins of the Kekura deposit,East Chukotka

The proportional mineralization effect was detected in the gold mineralization variability at the Kekura deposit. The presence of this effect complicates data interpretation and influences the methodology for studying the variography of the deposit. This paper presents a technique for the detection of this effect and methods for smoothing out this effect for further work with variography.