Six paragenetic associations on the basis of spatial-temporal relationships of lithotypes were recognized among the Upper Ordovician carbonate and terrigenous-carbonate rocks in sections of the Ilych River area, the Northern Urals. Their distribution characterizes frequent changes of depositional environments and the paleolandscape transformation of the carbonate platform outer margin during the Late Ordovician. In the Sandbian lime-lerrigenous mud was accumulated with activities of infauna (PA-1) at the continental slope foot of the platform-ramp. In the mid-Katian facially differentiated and diverse reef ecosystem (PA-2, PA-3) formed on the platform-shelf margin in a shallow environment. In the late Katian, in the conditions of the open platform-ramp, transgressive facies of carbonate sediments, concluding not only various fauna, but also periodic supply of debris from raised areas of the upper ramp, were accumulated (PA-4, PA-5). The Hirnantian is initially characterized by periodic eroding of the platform-shelf margin, and later by the accumulation of shallow crinoidal sands. Change of the paragenetic associations in succession reflects the lithogeodynamic evolution of the carbonate platform from the continental slope deep-water batyal to shallow-water environments of the platform-shelf during the Late Ordovician history of the northeastern European Platform.
Keywords:lithotypes, rock paragenetic associations, depositional environments, Upper Ordovician, Ilych River, Northern Urals.
The paper presents the results of lithological studies and the first data on carbon and oxygen isotope composition in limestones of Visean deposits at the eastern outcrops (Ilych River, Northern Urals). The main part of studied rocks are represented by different types of limestone: bioclastic and oolitic wackestones and grainstones, peloids wackestones and calcareous rudstones. Sometimes limestones are variosly dolomitized and silicified. Fine-grained quartz sandstones and claystone occur in the lower part of the studied section.
A total of 144 samples of limestones have been analysed for their carbon and oxygen isotopic values: d13СDPB = –2.9...+4.2 ‰ and d18ОSMOW = +23...+28.5 ‰. Most of these values are located within Visean marine carbonates of the East European platform and the Urals. Variations in the carbon and oxygen isotopic composition of limestones are in some extent consistent with the revealed trend of changes in the conditions of sedimentation in the Eastern Upper Pechora paleobasin in Visean.
In Visean at the observed area the sedimentation occurred within shallow-water carbonate shelf. The transition from terrigenous to calcareous sedimentation occurred in the period of maximum transgression within Radaevkian-Tulian time. It took place gradually with a few short-lived inversions. Similarly this transition was reflected by the isotopes composition. Change curves of average values d13С have the form of a sine wave with an amplitude within +2.4...+3.9 ‰. Average values of d18О vary linearly from +23 to +27 ‰. Almost until the end of the Mikhailovian time the conditions of sublittoral sedimentation dominated. At this time there was a gradual shallowing of the sea. Сoncurrently, the value of carbon isotopes become heavier from +0.9 to +3.6 ‰ to the mid-Aleksinian, and later d13C = +3 ± 0.25 ‰. At the end of Mikhailovian time the Islands area was formed nearby the Ilych River basin. This change of condition of sedimentation is well reflected in the isotope system of the carbonate rocks. The isotopic composition of carbon have a sharp relief from +3 to –2.9 ‰ and d18О has a small relief from +26.5 to +25 ‰.
The object of our study is Nemuryugan suite in Upper Riphean Central Tectonic zone of the Polar Urals. These rocks are characterized by scarn and high gold content. The formation conditions of ore mineralization are still poorly known. We studied primary composition and formation conditions of Nemuryugan suite. The rocks are phyllite, shale, quartzite, carbonate-epidote-quartz-albite-chlorite rocks, carbonaceous quartz-carbonate rocks and marble. Phyllitic shales are divided into non-carbonate and carbonate varieties. They consist of clay and a fraction of aleurites. Prototypes for epidote-quartz-albite-chlorite shales are tuffs of intermediate and basic composition. Phyllitic quartzite and shales are geochemically similar to, respectively, silicon and silicon terrigenous formations of underlying Nyarovey series, as well as to subduction granitoids and gneisses of Precambrian greenstone belt. Supra-subduction granitoids are parent species. The protoliths of Nemuryugan suite formed in the deep water part of the back-arc sea.
Lithological and micropaleontological (diatom and palinological analyses) study, radiocarbon dating of the stratified bottom sediments forming facially heterogeneous sedimentary sequences in a small lake isolated basin located within the limits of Kolvitsa Graben on the Oleniy Island in Kandalaksha Bay of the White Sea were carried out. We established that the stratigraphy of the facies of heterogeneous strata in the studied basin had been determined by the Late Holocene regression of the sea. Radiocarbon dating of facial transitions allowed identifying the time of isolation of the lake depression from the sea. We found out that the rate of earth’s surface elevation in the study area? associated with the Oleniy Island, had been larger than in other Kandalaksha Bay coastal areas with similar altitudes. These differences were caused by the differentiated neotectonic movements of the morphotectonic blocks.
Keywords:Kandalaksha Bay, small lake, bottom sediments, Holocene, lithology, miсropaleontology, neotectonics.
The shape of the crystal depends not only on its internal structure, but also on the external conditions that can be both isotropic (chemical composition, temperature, etc.) and anisotropic (heterogeneous matrix, oriented stress, etc.). In the latter case, the inhomogeneous character of the medium can be described, for example, in terms of the Curie limit groups.
There is a more specific case — the growth of one crystal inside the other. As a result the shape of crystalline inclusion shows the action both internal medium and external one. The question of the diversity of the external symmetry of crystals growing in crystalline media was first posed and solved by I. I. Shafranovsky for several specific cases.
In this paper the solution of the Shafranovsky problem is given. The complete table of variety of external symmetry of crystalline inclusion inside monocrystalline matrix was obtained.
The technique of express crystal morphological analysis, based on a cylindrical goniometer, is described. For a goniometer, a grid and a template are calculated, which allow calculating the face indices as well as the crystallographic zones. Using the example of a rounded diamond of the Ural type and a calcite, express methods for calculating the crystallographic parameters of the curvilinear and plane-faced crystal forms are shown.
The article deal with the results of study of the mineral pigments (white, red, and blue in color) from the carved icon «Golgotha Cross» (?19-th century). The relevance of study of the mineral pigments of the icon is conditioned by the use material from the deposits of red ochre near the Skitskaya village, Komi Republic. Three of stages of painting were deciphered. The carved wood surface was covered by the first layer of ceruse up to 0.3 mm thick. А colorful layer of pigments in red and blue was applied оn the ground. Thickness of pigment layer depended on preservation, is up to 0.2 mm. The pigments were studied by Raman spectrometry, XRD and EDS. X-ray diffraction indicates cerussite PbCO3. EDS and XRD allow us detecting white lead as main component of the pigments. Red pigment is minium. Raman spectrometry and XRD allow detecting prussian blue as main component of the blue pigments. Dark color of the icon is caused by the uppermost protective layer composed of lacquer or boiled linseed oil. The study of composition of the pigments allows supposing that exotic (imported from another region) pigments were used in icon painting by the Old Believers in Komi region in the 17th—19th centuries.
Keywords:carved wooden icon, mineral pigments, minium, berlin blue, Velikopozhensky monastery.