Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline

The results of investigations of Upper Vendian?Lower Cambrian deposits in the northeastern part of the Baltic monocline specify views on the evolution of depositional environments of sedimentary successions constituting the basal part of the sedimentary cover in inner areas of the northwestern East European Platform. It is shown that the Late Vendian and initial Cambrian were characterized by the consecutive influx of relatively mature terrigenous detrital material that originated from both the weathering crust of the Baltic Shield and new sources. Its deposition was interrupted by notable, although likely asynchronous, hiatuses, which are registered at the base of the Upper Vendian Vasileostrovskaya and Voronkovo formations and Lower Cambrian Lomonosov Formation. In the Late Vendian, sedimentary material was transported from the Baltic Shield, while beginning from the initial Early Cambrian the additional contribution to the formation of the sedimentary cover of the Baltic monocline was provided by coarse-grained sedimentary material from the Timan margin of the Baltica as follows from U?Pb isotopic ages obtained for detrital zircons. At the same time, lithogeochemical parameters of fine-grained rocks experienced no substantial changes.     

Clarkes of concentrations of trace elements in the Riphean fine-grained terrigenous rocks of the Uchur-Maya region and the Yenisei Range

The clarkes of concentrations (K_c) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) were analyzed for fine-gained terrigenous rocks (mudstones, metapelites) from the reference Riphean sections of the Uchur-Maya region and the Yenisei Range. It was established that the shales and mudstones of the Uchur and Aimchan groups in the Riphean hypostratotype section are characterized by moderate (2.5 < K_c < 5) and intense (K_c > 5) geochemical specialization for Li, B, and Zn. At the same time, the similar rocks of the Lakhanda and Ui groups do not exhibit any distinct geochemical specialization, although they are notably enriched in HREE. The metapelites from the basal formations of the Riphean sedimentary successions in the Yenisei Range are distinctly specialized for B and slightly for Li, Rb, Be, Nb, Ta, Th, Ge, and Cd. In addition, moderate specialization for Cu is characteristic of the metapelites from the Korda and Lopatino formations; for Bi, Sb, Hg, and V, for their analogs from the Potoskui Formation; and, for Hg and Cs, for the similar rocks from the Lopatino Formation. The metapelites of the Lower Riphean Korda Formation from the central zone of the Yenisei Range have elevated contents of significantly more elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, and others) than their counterparts from its eastern near-platform part. The mudstones of the ore-bearing (Pb, Zn) Gorevo Formation are characterized by elevated concentrations of several ore elements such as Pb, Cd, As, Sb, and Bi. The elevated K_c values of the rare lithophile and of several ore elements in the metapelites of the Yenisei Range are determined by the high geochemical differentiation of the Early Precambrian blocks constituting the western margin of the Siberian Craton, which were eroded in the Riphean, and the syn-sedimentary riftogenic and intraplate magmatism. On the contrary, the fine-grained and terrigenous rocks from the basal part of the Riphean section in the Uchur-Maya region are compositionally closer to the immature Late Archean substrates or their Early Proterozoic analogs.     

The Influence of Moon Phases on the Frequency of Admissions to a Psychiatric Hospital

Izvestiya, Atmospheric and Oceanic Physics - The influence of the moon phase on persons with mental disorders and the frequency of emergency and urgent admissions to the mental hospital in the city...     

The Sr isotopic characterization and Pb-Pb age of carbonate rocks from the Satka formation,the Lower Riphean Burzyan Group of the southern Urals

The Rb-Sr and U-Pb systematics are studied in carbonate deposits of the Satka and Suran formations corresponding to middle horizons of the Lower Riphean Burzyan Group in the Taratash and Yamantau anticlinoria, respectively, the southern Urals. The least altered rock samples retaining the ⁸⁷Sr/⁸⁶Sr ratio of sedimentation basin have been selected for analysis using the original method of leaching the secondary carbonate phases and based on strict geochemical criteria of the retentivity (Mn/Sr < 0.2, Fe/Sr < 5 and Mg/Ca < 0.024). The stepwise dissolution in 0.5 N HBr has been used to enrich samples in the primary carbonate phase before the Pb-Pb dating. Three (L-4 to L-6) of seven consecutive carbonate fractions obtained by the step-wise leaching are most enriched in the primary carbonate (in terms of the U-Pb systematics). In the ²⁰⁶Pb/²⁰⁴Pb-²⁰⁷Pb/²⁰⁴Pb diagram, data points of these fractions plot along an isochron determining age of 1550 ± 30 Ma (MSWD = 0.7) for the upper member of the Satka Formation. The initial ⁸⁷Sr/⁸⁶Sr ratio in the least altered limestones of this formation is within the range of 0.70460–0.70480. Generalization of the Sr isotopic data published for the Riphean carbonates from different continents showed that 1650–1350 Ma ago the ⁸⁷Sr/⁸⁶Sr ratio in the world ocean was low, slightly ranging from 0.70456 to 0.70494 and suggesting the prevalent impact of mantle flux.     

The Southern Urals Large Igneous Province with an age of approximately 1380 Ma: Precision U–Pb ID-TIMS constraints

The formation of the Large Igneous Province (LIP) approximately 1380 Ma old in the South Urals was related to the Mashak riftogenic event in the Bashkir meganticlinorium, which was synchronous with the emplacement of different magmatic bodies (the Berdyaush pluton of rapakivi granites and associated rocks, the Main dike of the Bakal ore field, and the Medvedev, Guben, and Kusa massifs, among others) localized among sedimentary deposits of the Burzyan and Yurmatin Groups representing Lower and Middle Riphean type units of northern Eurasia. The U–Pb ID-TIMS age of 1379.6 Ma (MSWD = 1.3) obtained with an accuracy of ±2.9 Ma (confidence interval 95%) combined with the available published U–Pb ID-TIMS data constrain the age and duration of the Early–Middle Riphean pulse in the LIP formation in the Southern Urals.     

Pre-Riphean metapelites of the Yenisei Range: Chemical composition,sources of eroded material,and paleogeodynamics

The paper reports data on metapelites (gneisses and crystalline schists) from various Early Precambrian lithostratigraphic units of the Yenisei Range (Kan and Yenisei complexes, Garevka Unit, and Teya Group). A representative selection of 57 samples from the examined vertical section were analyzed for major oxides, LILE, transition elements, HFSE, REE, radioactive elements, and other trace and minor elements. The most important distinctive geochemical feature of metapelites composing most of the vertical section is their elevated concentrations of Al, which are higher than in the Post-Archean Australian Shale (PAAS), K, Rb, Ba, Ga, Sc, Pb, Th, Nb, Y, and REE. These data and the systematics of elements in certain discriminant diagrams testify that the metasedimentary complexes in the sedimentation basin and the rocks associations composing the erosion area (crystalline massifs of the ancient basement of the Siberian craton) were strongly geochemically differentiated and mature. The composition of the eroded crustal material was close to the average composition of the post-Archean continental crust and PAAS. The metapelites of the Kuzeeva Unit in the Kan Complex and Penchenginskaya Formation in the Teya Group were the only ones that could have basic rocks as an additional source of material, as also follows from the elevated Cr concentrations of the rocks and their REE systematics. The three types of REE patterns of the metapelites largely correspond to the composition of the rocks that composed the ancient drainage areas and the degrees of the differentiation and averaging of their terrigenous material. The first predominant type corresponds to PAAS and the averaged composition of the upper continental crust. The second and third types of the REE patterns with high and low La_N/Yb_N ratios, respectively, and with or without negative Eu anomalies provide evidence of the contribution of tonalite-trondhjemite-granodiorite (TTG) or basite sources typical of granite-greenstone provinces. In certain diagrams, the compositional fields of Early Precambrian metapelites in the Yenisei Range almost exactly coincide with the compositional fields of regional fine-grained Riphean terrigenous rocks. This suggests that the Late Precambrian sedimentary rock sequences inherited their geochemical features from more ancient rocks. The reproduced ancient geodynamic environments in which the Early Precambrian metaterrigenous complexes of the Yenisei Range were accumulated correspond to ensialic continental marginal basins. The rocks of the Kan and Yenisei complexes and the Garevka Unit were formed mostly on active continental margins and, less frequently, on passive margins. The protoliths of metasedimentary rocks of the Teya Group were accumulated in a subplatform environment at a passive margin.     

Glaciogenic and related sedimentary rocks: Main lithochemical features. Communication 1. Late Archean and Proterozoic

Lithochemical features of the Late Archean, Paleoproterozoic, and Neoproterozoic glaciogenic and related sedimentary rocks around the world are considered. Based on comparison with the average Post-Archean Australian Shale (PAAS), it is shown that the bulk chemical composition of diamictites reveals no specific lithochemical characteristics that would undoubtedly suggest their formation under cold climatic conditions. The chemical index of alteration (CIA) frequently applied in different paleoclimatic reconstructions should be considered as additional (though sufficiently important) tool, because its values for each analyzed object show significant variations mainly controlled by local factors.     

Lithogeochemical features of Riphean fine-grained terrigenous rocks in the Kama-Belaya aulacogen and their formation conditions

Lithogeochemical features of Riphean fine-grained terrigenous rocks of the Kama-Belaya aulacogen are discussed. It is shown that aluminosiliciclastic material delivered to the aulacogen during the Riphean was characterized by a low maturity degree. The successively increasing K₂O/Al₂O₃ values in the Riphean summary section correlate negatively with the CIA index values, indicating a gradually strengthening tendency for climate aridization in erosion zones. Data on some indicator ratios of trace elements and REE systematics in Riphean silty mudstones and shales of the Kama-Belaya aulacogen imply the involvement of mafic and ultramafic rocks, in addition to acid igneous and metamorphic varieties, in erosion during accumulation of the Nadezhdino, Tukaevo, Ol’khovka, Usinsk, and Priyutovo formations. Comparison of data on the composition of rocks in provenances based on the mineralogical-petrographic study of sandstones and investigation of geochemical features of silty mudstones and shales revealed their sufficiently high similarity. The geochemical data made it possible to specify the composition of rocks in provenances. Low Ce/Cr values in the fine-grained terrigenous rocks of the Lower Riphean Kyrpy Group suggest their formation with a significant contribution of erosion products of the Archean substrate, which is atypical for higher levels of the section. Thus, the Early-Middle Riphean transition period was likely marked by substantial changes in the mineral composition of material delivered to the Kama-Belaya aulacogen. The lack of exhalative components in the examined specimens of silty mudstones and shales points to a relatively low permeability of the Earth’s crust in the eastern East European Platform through the entire Riphean.     

Lithochemical composition of sandstones of the Vendian Asha Group,South Urals

The mineralogical–petrographic and chemical study of sandstones of the Vendian Asha Group in the Bashkir anticlinorium, the western slope of the South Urals, showed that this large stratigraphic unit consists of sedimentary associations formed in different conditions: (1) Pre-Uryuk sediments (Tolparovo, Suirovo, and Bakeevo formations) accumulated during marine regression possibly in the course of significant glacioeustatic sea level fluctuations and formation of the foredeep of Timanides. (2) Sediments of the Uryuk Formation, including alluvial and several related sediments. Analysis of the Qm–F–Lt, Qt–F–L, and ln(Q/L + CE)–ln(Q/F) diagrams showed that they were derived from magmatic/plutonic rocks in the inner parts of the East European Craton. Based on the distribution of data points of psammites in the Qt/(F + R)–Qp/(F + R) diagram, they were accumulated in the semihumid/semiarid conditions. (3) Coastal, shallowmarine, and fluvial/proluvial (?) sediments of the Basa, Kukkarauk, and Zigan formations. They were formed by the erosion of provenances located supposedly east of the present-day Bashkir anticlinorium. The psammites of the Asha Group were analyzed using the sandstone formation model proposed models proposed in (Dickinson et al., 1985; Garzanti et al., 2007). The distribution of data points of psammites from three uppermost formations of the Asha Group in the Qm–F–Lt and Qt–F–L diagrams suggests that they were accumulated by the redeposition of erosion products of the so-called clastic wedges of recycled orogens (clasticwedge provenance) made up of the fluvial and turbidite complexes of the foreland, fore-arc, or residual oceanic basins.