Aromatic biomarkers of sterane and hopane series in Upper Devonian oils and bitumoids of Domanik deposits of the Timan-Pechora basin A. A. Derevesnikova, D. A. Bushnev, N. S. Burdelnaya
We discussed results of study of aromatic hydrocarbons-biomarkers in the Upper Devonian oils and bitumens of the Domanik deposits of the Timan-Pechora basin. We showed that the distribution of triaromatic steroids of C26—C28 composition in the oils was slightly different from that in the bitumens, while the distribution of saturated steranes of C27—C29 composition for the oils and bitumens was quite close. TA(I)/TA(I+II) coefficient, calculated for triaromatic steroids, showed a significant increase with the degree of maturity of the organic matter of the Domanik rocks, and its values for the oils testified to their formation at the beginning of the oil window, which did not contradict the data from saturated hydrocarbons-biomarker. All the studied oils and bitumens were characterized by a close distribution of aromatic 8,14-secohopanes and benzohopanes.
Vaesite (NiS2): the first finding in carbonatites V. G. Korinevsky
Information is given on the morphology, chemical composition and structure of crystals of rare nickel disulfide — vaesite (NiS2), first discovered in carbonatites. Prior to this, vaesite was found in rocks confined to ultrabasic and basic masiffs, or to hydrothermal veins. Vaesite was met in the form of single grains. The crystals, like other accessory minerals (phlogopite, tremolite, muscovite, pyrite, ruby, tourmaline), had an idiomorphic faceting, located in isolation from each other, or toward the growth zones of large calcite crystals. Most likely, all these minerals were crystallized from carbonate magma, which formed carbonatite dikes. The mineral from carbonatites differed from vaesite from other sites by a noticeable amount of Cu (about 9 wt.%), a small content of Fe (2—5 wt.%), and the absence of Co. X-ray diffraction characteristics of vaesite corresponded to its typical samples. The main rock-forming minerals (calcite and dolomite) and the main part of accessories (phlogopite, tremolite, muscovite, pyrite, tourmaline, ruby and vaesite) were formed simultaneously. A later association was represented by native sulfur, quartz, and fluorite, performing miarola cavities. The weathering crust on carbonatites containing nickel sulfides can serve as a source of nickel for silicate ores.
Global paleogeography and paleobiogeography of the Toarcian (Early Jurassic) on the brachiopods V. S. Grinenko, V. V. Baranov
This article is devoted to the actual problems of the global paleogeography and paleobiogeography in the Toarcian stage of the Jurassic period. The authors proposed a new model on the basis of spatio-temporal analysis of Toarcian brachiopods and materials of deep-sea drilling of the seabed of the World Ocean. It was established that in the Toarcian stage the paleogeography of the Earth was represented by three supercontinents Afalia, Pacifida and Arasa and two continents Hyperborea and Antarctida, which were separated by shallow shelf sea basins, about 2000—3000 km wide.
Completed paleoreconstructions showed the Boreal basin was connected to the Tethys West and East straits. Based on the analysis of climatic zonality and the spatial-temporal distribution of the Toarcian brachiopods three paleozoochories of higher rank Equatorial, Boreal, and Notal superrealms were distinguished. The Equatorial Superrealm was represented by the Alpine-Melanesian-Chinese and West-South American biogeographical realms, the first was divided into the Alpine-Caucasian, Sino-Japanese and Melanesian provinces. The Alpine-Caucasian province were represented by three subprovinces: European, North-African and Crimean-Caucasian-Arabian. Boreal superrealms is represented by the Siberian-Alaska realm and the Western Canadian province of the West-North American realms. The Nevadan province of this realm is part of the Equatorial Superealm. The New Zealand-New Caledonian realm in the Notal superrealm is included.
The first finding of foraminifera in Ludlowian carbonate rocks at the Ilych River (Northern Urals) N. A. Matveeva, R. M. Ivanova
The results of a microscopic study of the Upper Silurian carbonate rocks in the Ilych River (Northern Urals) have been represented in the article, which revealed primitive foraminifera for the first time. The description of paleontological material and distribution of foraminifera in the section was given. A total of 11 genera and 12 species of foraminifera were found. The study of Late Silurian foraminifera expanded the geography of distribution of Chitinolagena, Ordovicina and stratigraphic genera of the following species: Bisphaera primitive, B. ex gr. obscura, Parastegnammina cf. grandissima, Baituganella sp., Cribrotuberitina insueta. The most numerous representatives were foraminifera of genus Caligella among which the forms found in the carbonates of outcrop 112, were different in size compared to the specimens from reef limestone outcrops 110 and 111, which could probably be connected with unfavorable continental slope conditions.
Some features of internal structure of monodisperse spherical silica particles D. V. Kamashev, A. A. Kryazhev
We studied the deposition rate of monodisperse spherical silica particles and the volume of the supramolecular structure formed by them, which, together with the data on particle sizes and the amount of initial silica in the system, allowed calculating the real density of spherical particles. The obtained data indicated a significant number of voids in the structure of the particle, the volumetric values of which are within 30 %.
The nitrogen surface sorption method determined the specific surface area for supramolecular structures consisting of spherical silica particles of different sizes, from which the estimated particle sizes were calculated. The comparison of the obtained results with data determined by scanning electron, atomic force microscopy and dynamic light scattering showed that spherical particles had a surface area 30 % higher than the calculated one, which indicated the complex structure of silica particles and the presence of a system of hidden pores and voids. We interpreted the data taking into account the assumption of the hierarchical nature of the structure of spherical silica particles.
Cluster analysis in geology: metrics and measures Yu. L. Voytekhovsky
The article is devoted to cluster analysis, actively used in statistical data processing in geology, biology, and other natural sciences. Attention is drawn to the fact that the result of cluster analysis may significantly depend on the metric used, i.e. distances between points in multidimensional space. The distances between the point sets can be determined directly and by the measures of covering sets. The methodical resource of cluster analysis is seen in comparing the results when using different measures and metrics.