Zirconium-titanium placers of the Voronezh Anteclise: Types,epochs and factors of formation,and forecast

The early and late Frasnian, Barremian-Aptian, Cenomanian, early Santonian, early Campanian, and Oligocene-Miocene epochs of the formation of various types of zirconium-titanium placers are distinguished in the Voronezh Anteclise. The factors of their formation are considered, and a forecast of prospecting has been made. Lower Frasnian sedimentary rocks occur in the southeast, where the placers are related to the ilmenite-bearing volcanosedimentary rocks of the Yastrebovo Sequence. The upper Frasnian productive quartz sand of the Petino Sequence occurs in the central part of the Voronezh Anteclise. The Barremian-Aptian productive quartz sand and kaolinite clay occur in the northern and northeastern parts of the anteclise (Ryazan and Lipetsk oblasts). The placers formed in the Cenomanian are known in the Tambov oblast in the northeast of the Voronezh Anteclise and are related to phosphate-bearing glauconite-quartz sand. The early Campanian phosphorite-glauconite-quartz formation is widespread in the northwest of the Voronezh Anteclise at the junction with the northeastern wall of the Dnieper-Donets Basin (Bryansk oblast). The Oligocene-Miocene epoch was characterized by quartz sands abundant in the northwestern and south-western areas. The formation of zirconium-titanium placers is controlled by structural-tectonic, facies, volcanic, paleogeographic, stratigraphic, and evolutional factors. The indispensable condition for heavy mineral concentration is existence of positive forms of underwater topography. These are mostly structural elements of the third and fourth orders on the slopes of the Voronezh Anteclise at the boundaries of the adjacent negative structures. As concerns the facies factor, the occurrence of coastal and shallow-water marine facies with alternating and medium hydrodynamic activity and predominance of sand fractions 0.25–0.05 mm are criteria of elevated concentration of heavy minerals in sand. One of the conditions providing concentration of heavy minerals is a multiple rewashing of sands close to a relatively stable shoreline. The volcanic factor is determinant for the lower Frasnian marine placers fed by volcanic sources. The Cretaceous and Paleogene zirconium-titanium placers were formed owing to scouring of the older Paleozoic and Mesozoic sedimentary rocks of the Voronezh Anteclise, as well as the Baltic Shield, Moscow Syneclise, and the Volga-Ural Anteclise. The age of placers was estimated with accuracy up to substages (lower Aptian, lower Santonian, lower Campanian). The evolution factor is expressed in variation of localization and composition of placers in time and space. The forecast of potentially ore-bearing areas is based on optimal combinations of favorable factors.     

Modeling the Magnetic Anomaly of the Bosumtwi (Ghana) Complex Meteorite Crater by Taking Into Account the Impact Demagnetization and Morphological Features

Izvestiya, Physics of the Solid Earth - Abstract—The formation of impact craters on the Earth’s surface is accompanied by the effect of shock waves on rocks. The shock wave compression...     

Major and trace element zoning in plagioclase from Kizimen Volcano (Kamchatka): Insights into magma-chamber processes

The data on the geochemistry of the rocks of Kizimen Volcano and results of microprobe studies of major and trace elements in plagioclase grains from acid lavas and basalt inclusions are presented. The characteristics of the Kizimen Volcano are the following: (1) basalt inclusions are abundant in acid lavas; (2) banded, mixed lavas occur; (3) the distribution curves of rare-earth elements of acidic lavas and basalt inclusions intersect; (4) Sr-Nd isotope systematics of the rocks and inclusions do not indicate mixture with crustal material; (5) plagioclase phenocrysts are of direct and reverse zonation; (6) olivine and hornblende, as well as acid and mafic plagioclases, coexist in the rocks. The studies revealed that the rocks are of a hybrid nature and originated in the course of repeated mixture of acid and mafic melts either with chemical and thermal interaction of melts or exclusively thermal ones. Study of the major- and trace-element distribution in zonal minerals provides an informative tool for understanding the history of the generation and evolution of melts in a magma chamber.     

REMOTE SENSING IMAGERY IN THE STUDY OF SETTLEMENT ON ALLUVIAL FANS

The authors describe how remote sensing imagery may be employed in the zonation and mapping of the alluvial fans of the Fergana Basin, USSR. Settlement patterns depicted on these maps can then be analyzed by planners and civil defense personnel with a view toward minimizing risks posed by natural hazards endemic to alluvial fans: mudflows and other seismically triggered mass movements. Translated from: Geografiya i prirodnyye resursy, 1987, No. 3, pp. 50-55.     

Structure of the Fram Strait branch of the boundary current in the Eurasian Basin of the Arctic Ocean

Recent mooring-based observations at several locations along the continental slope of the Arctic Ocean's Eurasian Basin showed a transformation of the Boundary Current (BC) from a mostly barotropic flow in Fram Strait to a jet-like baroclinic current northeast of Svalbard, and the reemergence of the barotropic structure of the flow in the eastern Eurasian Basin. This transformation is accompanied by a weakening of the flow from ～24 cm/s in Fram Strait to ～5 cm/s at the Lomonosov Ridge. The maximum of the baroclinic component of the BC at an intermediate depth (～200–370 m) is associated with the Atlantic Water core. The depth range of the baroclinic current maximum is controlled by cross-slope density gradients above and below the baroclinic velocity maximum as follows from the geostrophic balance of forces. According to the model simulations, the BC splits into shallow and deep branches in the proximity of Svalbard due to a divergence of isobaths, confirming topographically-controlled BC behavior. The shallow branch is located at a shelf break with a typical bottom depth of ～200 m and current speed of up to ～24 cm/s. The discussed results, which provide insight on some basic aspects of the dynamics of the BC (the major oceanic heat source for the Arctic Ocean), may be of importance for understanding of the ocean's role in shaping the arctic climate system state.     

Stages of Tectono-Magmatic Activity in the Border Zone of the Siberian Platform and the Tannuola–Khamsara Segment of the CAFB (According to the Results of U–Pb Isotope Studies)

Doklady Earth Sciences - Based on the dating of metamorphic and igneous rocks of the northeastern part of the Khamsara terrane, the main stages of tectono-magmatic activity at the border of two...     

Influence of agricultural development and climate changes on the drainage valley density of the southern half of the Russian Plain

The southern half of the Russian Plain is characterized by a relatively short history of intensively ploughed lands.The duration varies from approximately three centuries in the southern part of the forest zone to less than one century in some parts of the steppe zone.It was found that after cultivation,on more than 40％ of lands in river basins the drainage valley density (Ddv) decreased by 15-58％ in all landscape zones.In the first stage,the Ddv decrease was mostly associated with increasing surface runoff coefficient after cultivation of virgin lands with proportional decreases in groundwater runoff.In the second stage,usually after reaching areas of arable lands in river basins ＞ 60％,the volume of eroded sediments entering small fiver channels exceeded the transport capacities of the permanent water-courses.As a result,the river channels completely silted.In later stages,the sediment redistribution cascade within the small river basins of the Russian Plain stabilized because of the increasing proportion of sediment eroded from the basin areas and re-deposited before entering the river channels because of the increasing area of sediment sinks due to the increase in dry valley lengths and total areas.The morphological parameters of small valleys and groundwater discharges are the key parameters that affect the intensity of small river aggradation on the regional scale.     

A field experiment on modeling the impact of aerosol layers on the variability of solar insolation and meteorological characteristics of the surface layer

Described are the results of a field experiment carried out in 2010 on studying the impact of artificial aerosol formations on the solar insolation intensity and thermal characteristics of the atmospheric surface layer. The composition of the measuring equipment complex is given and the results of the experiment and its theoretical analysis are presented. It is demonstrated that the solar radiation flux decrease results in rather rapid response of the surface air layer manifesting itself in the considerable decrease in temperature and turbulent heat fluxes. The theoretical estimates corroborate the obtained experimental data. The field experiment is the continuation of researches carried out in 2008 and 2009.     

Sequence-stratigraphic analysis of the Aptian deposits in the valley of the Mzymta River

In this work, based on the example of a well drilled in the valley of the Mzymta River (Northwest Caucasus) the possibilities of the sequence-stratigraphic method are demonstrated for the first time. This method allows us to clarify the natures of numerous repetitions in the same interval of the geological sequence (modern, ancient landslide or syn-sedimentary-landslide, and tectonic or eustatic). In addition, the geochemical characteristics of bituminous sediments are given. The sequence that was studied in the well shows the complex polygenetic evolution of sediments since Aptian time and the oceanic anoxic event-1.