Nd isotope systematics of the Vendian–Early Cambrian sedimentary ores in the northern segment of the Paleoasian Ocean

Isotope–geochemical studies of Mn, P, and Ba ores were performed in order to establish the influence of submarine hydrotherms on the formation of Early Cambrian sedimentary rocks of the southern environs of the Siberian Platform. Based on study of the geochemical and isotope (ε_Nd) characteristics of the shallow-water Mn and Ba ores and phosphorites of southern environs of the Siberian Platform with similar ages, two types of sedimentary basins of the different geodynamic origins were distinguished: intraplate oceanic and those of the active continental margin, for which the sources of ore materials differ by the proportions of the mantle and contaminated crustal matter.     

Sr chemostratigraphy of carbonate sedimentary cover of the Tuva-Mongolian microcontinent

This study uses Sr isotope chemostratigraphy to place constraints on the depositional age of carbonate rocks from the Tuva-Mongolian microcontinent. The age of carbonate rocks of the Irkut Formation (⁸⁷Sr/⁸⁶Sr initial ratio equal to 0.70480–0.70485) is determined to be older than 1250 Ma, whereas carbonates of the Zabit (0.70706–0.70727 and 0.70828–0.70848) and Agarin Gol (0.70725–0.70743) formations were deposited in the interval 630–560 Ma.     

Diffuse Pollution of Water Bodies and Estimation of Export of Biogenic Elements under Different Scenarios of Water Use in the Watershed

Water Resources - The notion of diffuse pollution process in water bodies of different dimensions is formulated. An algorithm is given for calculating the average annual volume of the export of...     

Upper Campanian-lower Maastrichtian sections of the northwestern Rostov region. Article 1. Description, paleontological assemblages, and lithobiostratigraphy

Four upper Campanian-lower Maastrichtian reference sections are described in the Glubokaya and Kalitva river basins and in the Znamenka 1-A Borehole located in the northwestern Rostov region. The sections are composed of the upper Campanian Kagal??nik, Belgorod, Pavlovka, Sukhodol and lower Maastrichtian Efremovo-Stepanovka formations. They are characterized by successive stratigraphically significant macro- and microfossil assemblages: belemnites, calcareous nannoplankton, benthic foraminifers, and radiolarians. The Pavlovka and, particularly, Sukhodol formations contain a specific assemblage of coarsely-agglutinated benthic foraminifers. The first data obtained on radiolarians in upper Campanian-lower Maastrichtian sections of the northwestern Rostov region revealed four assemblages, two of which were previously unknown from Upper Cretaceous sediments of the East European Platform. Most sections enclose a hiatus at the base of the Sukhodol Formation, which comprises two upper Campanian benthic foraminiferal zones. The problem of recognition of the lower Maastrichtian boundary on the East European Platform is considered in accordance with international GSSP requirements.     

Main Features of the Historical Metallogeny of Niobium

Doklady Earth Sciences - Niobium metallogeny over the course of geological history has been considered on the basis of data from 45 largest deposits in the world belonging to any of three...     

Metallogenic specialization of supercontinent cycles: A case study of silver deposits

The distribution of integrated resources of large and superlarge mineral deposits (LSLDs) of silver, where the main part of industrially recoverable silver reserves is concentrated, is compared with the existing model of supercontinent cyclicity over the geological history of the Earth. It is found that each supercontinent cycle (Kenoran, Columbian, Rodinian, Pangean, and Amasian) is particularly expressed in the silver metallogeny. The significant intercycle variations in the numbers of LSLDs, diversity of types of these deposits, accumulated resources, mean tenors of silver in ores, and some other numerically expressible characteristics are revealed. These variations correlate with a number of geohistorical changes in the conditions under which endogenous and exogenous geological processes run.     

The problems of radiolarian-based dating of Jurassic-Cretaceous siliceous rocks from accretionary complexes,the Russian East

Radiolarians, which represent the most widespread fossil faunal group in jaspers and cherts, are the best tool for determining the geological age of Jurassic-Cretaceous volcanogenic-siliceous sequences in the Pacific margin of Russia, because they meet all the conditions required for orthostratigraphic groups, i.e., demonstrate rapid evolutionary changes of their assemblages, completeness of their record through the geological section, and a wide lateral distribution. The selection of biostratigraphic scales for determining the age of radiolarian assemblages is of principal significance. The significant difficulty in correlating Tethyan and Pacific assemblages is similar to that appearing in the case of the correlation between the Tethyan and Boreal ammonite standards. The existing discrepancies are explained by the different life spans of some guide species that determine the stratigraphic range of particular zones in their geographic type areas and may be different in other paleobiogeographic regions and provinces. The program of scientific studies should include the search for and thorough analysis of Jurassic-Cretaceous sections in Russia that contain simultaneously radiolarians, buchians, and ammonites. Such sections might provide the possibility for developing a single scale for the transitional sections and outlining ways for correlating the Tethyan and Pacific assemblages.