Novel U-Pb isotopic zircon data on the rhyolite of the Saf’yanovskoe Cu-Zn deposit (Middle Urals)

Research subject. Zircons from the Saf’yanovskoe Cu-Zn deposit rhyolite (Middle Urals). For the first time, zircon U-Pb dating for the rhyolite of the ore-bearing volcanic-sedimentary rocks of the Saf’yanovskoe deposit was performed. The volcanites are characterized by an andesite-rhyodacite composition and are localized at the southern edge of the Rezhevskaya structural-formation zone (SFZ) of the Eastern Ural megazone. A number of publications assign these rocks either to the basalt-rhyolite formation of the Middle Devonian, or to the basalt-andesite-dacite-rhyolite formation of the Lower-Middle Devonian.Aim. To estimate the age of the ore-bearing volcanic rocks under study using the U-Pb SHRIMP-II isotop ic system of zircon from the rhyolite of the eastern side of the Saf’yanovskoe deposit. By its chemical composition, the rhyolite belongs to the silicic varieties of subvolcanic rocks. Methods and results. The U-Pb isotopic system of zircon was studied by 5-collector mass-spectrometer of high precision and emission of the secondary ions SHRIMP-II (ASI, Australia) in the VSЕGEI Institute. U-Pb relations were investigated by a procedure developed by I.S. Williams. The U-Pb data obtained based on 13 zircon grains showed the age of 422.8 ± 3.7 Ma. Conclusions. The U-Pb dating of zircon obtained previously from the lens-shaped andesite bodies of the western side of the Safyanovskoe deposit gave the age of 422.8 Ma, which corresponds to the Przydoli series epoch of the Upper Silurian. We established that, among the volcanic rocks of the Saf’yanovskoe deposit, the effusive formations of the Upper Silurian are present.

The Pridoli (Silurian) Lithostratigraphy and Biostratigraphy of Gorny Altai

—The paper presents new data on the upper Silurian litho- and biostratigraphy of the Gorny Altai area. Sediments within this interval store a succession of taxonomically representative middle–upper Ludfordian, lower Pridoli, and Lower Devonian (Lochkovian–Pragian) conodont assemblages. The new fauna constraints made a basis for updated correlations of the local and regional stratigraphic units at the Silurian/Devonian boundary of Gorny Altai with the stages of the International Stratigraphic Chart. The correlation results reveal a mismatch between the boundaries of the local and regional Silurian units and the respective boundaries of stages in the International Stratigraphic Chart.

Early land plants from the Lower Devonian of central Victoria, Australia, including a new species of Salopella

Early land plants with elongate sporangia held in the palaeobotanical archives of Museums Victoria were examined. The fossil plants are from Yea (?upper Silurian) and near Matlock (Lower Devonian) in central Victoria, and are of interest because they contribute to our understanding of the evolution of early land plants in a region in which research has been limited. Both Salopella australis and Salopella caespitosa were originally described over 30 years ago and this reinvestigation has resulted in the emending of the diagnosis of Salopella australis and the erection of a new morphotaxon Salopella laidae sp. nov. based primarily on differing branching architecture and sporangial morphology. Salopella laidae comes from Yea Formation and possesses regular isotomous branching over at least two orders of branching, terminating in elongate sporangia that are wider than their subtending axes, differing from S. australis, which possesses only one dichotomy emanating from at least two erect parallel parent axes with sporangia that are the same width as their subtending axes. A recently collected specimen of Salopella caespitosa was also examined and adds to our understanding of this taxon, which was previously only known from one specimen. Consideration is given to the possible sources of these early land plants based on other early land plants with a similar grade of organisation.

CORRELATION OF THE SILURIAN SEQUENCE OF THE 25-KOTYUZHINY STRUCTURAL WELL WITH THE DNIESTER REFERENCE SECTION OF THE SILURIAN IN THE VOLYN-PODILLYA PLATE

The paper is devoted to lithostratigraphic and biostratigraphic subdivision of the Silurian deposits of 358 m total thickness in the 25-Kotyuzhiny structural well and its comparison with the stratotypic Dniester section of the Silurian system in accordance with Legend to the geological map of Ukraine, the Volyn-Podolsky series of 1: 200 000 scale, consistent with the latest modernization of Silurian stratigraphic charts. The described section is a parastratotype for Silurian litho-stratons of the Kovel-Khotyn structural and facies zone and a reference one for Silurian deposits in the central part of this zone. The Silurian in the 25-Kotyuzhiny well is represented by the lower (Llandoverian and Wenlockian stages) and upper (Ludlovian and Przhidolian stages) series. According to the lithological-facies composition and sedimetantaion conditions during Silurian times, there are 3 major completed stages of sedimentation as transgressive-regressive cycles, corresponding to the the Yarugian, Malinovetsian and Rukshinian series, which are quite clearly subdivided into 10 suites and 12 sub-suites. In correlation with the Dniester reference section, litho-stratons of the Silurian are characterized mainly by carbonate and clay-carbonate composition, relative stable thickness and facies pattren, diversity of fauna with a predominance of shallow benthic forms. The well is characterized by bituninous manifestations indicating hydrocarbon potential of the area and its prospectivity for shale gas accumualtions in the formations of the upper Silurian in particular.

Lithological and isotopic (δ 13C and δ 18O) features of the Upper Silurian back-reef lagoon deposits of the Ilych River Basin, the Northern Urals

The Upper Silurian is widely developed in the Northern Urals, where it is represented by various facies. The continental slope facies and the reef shoal facies are well documented in the geological literature, while as back-reef lagoon facies have not yet been characterized in detail. The studied objects included two sections of the back-reef deposits in the Ilych River basin. In this work, we characterize rock types the make up the sections, and their isotopic characteristics. The Late Silurian back-reef lagoon was characterized by a mosaic sediments distribution, which included the island areas between which there were areas with a quiet hydrodynamic regime. In the latter, mainly muddy carbonates were accumulated, represented by clotted fenestral limestones. The area of small islands was characterized by a wide distribution of lime sands, which clastic material was derived from probable paleosoil carbonates. They are characterized by slightly increased δ 13C values, which, probably, reflects isotopic fractionation at the evaporative geochemical barrier. Dolomitization and karstification are described among secondary alterations in the studied sections. Cementstones is interpreted as karst cavities precipitates.