pdf № 347, November

DOI: 10.19110/geov.2023.11.1

The article review the geochemistry of rare earth elements (REE) in sedimentary marine carbonates (limestones and dolostones) with respect to using the cerium anomaly as a proxy for redox conditions in ancient seawater. The physicochemical properties of REE and Y, the problem of normalizing their contents in sediments, behavior in the World Ocean and in chemogenic deposits, the origin of La, Ce, Eu, Gd anomalies and their calculations, sample preparation techniques, contamination problem and the influence of non-carbonate REE+Y-hosting phases to whole rock and acidic leachate compositions, as well as criteria for determining seawater-like pattern are considered.

Keywords: REE and Y, fractionation, normalization, seawater, seawater-like pattern, contamination, anomalies of Ce, Eu, La, Gd, redox conditions.

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DOI: 10.19110/geov.2023.11.2

This work represents the results of multidisciplinary study of paleosols from the weathered roof of Precambrian basement (Stary Oskol, Belgorod region). Shallow paleosols were developed from ferruginous shale and diagenetically modified weathering crust of ferruginous quartzite which led to its sideritization. At the studied location (quarry of the Stoilensky mining and processing plant) the age of weathering crust is pre-Devonian. Both rocks contain pyrite. Paleosols developed under similar primitive lithophytic vegetation. The studied paleosols are identified as in situ, biotic, of extreme pedogenesis. The trigger for their development was the pyritization. As a result, the chemical weathering prevailed under physical and biological ones. Both soils were attributed to acid-sulfate. Paleosols have not developed the continuous cover. The paleosols previously discovered in this area were developed from ferruginous quartzite and are also attributed to the acid-sulfate type. It seems that this soil type was widely distributed in the past.

Keywords: weathering crust, sulfides, acid-sulfate paleosol, berthierine, gypsum, Fe-minerals.

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DOI: 10.19110/geov.2023.11.3

The results of the study of calcite microspherulites in carbonate breccia formed at the junction of biohermal and bioclastic limestones (Lower Maeotian, Cape Kazantip, Kerch Peninsula), the nature of which is still being discussed, are presented. The following analytical methods were used: chemical carbonate, gas chromatography, Raman spectroscopy, electron microscopy with EDS, isotope. The studies resulted in the following: the presence in the fossilized biofilms of the pelitomorphic matrix and microspherulites of framboidal pyrite, halite, barite, celestine, dolomite-calcite, hematite and magnetite, which are absent in the other structural components of the breccia. Organic matter (OM) is represented by algal-cyanobacterial matter with a large contribution of the microbial component and an admixture of humic material. The carbonaceous matter in calcite microspherulites is actually characterized by primary unstructured organic matter. The accessory minerals zircon, oligoclase, rutile, neodymium-cerium monazite and vanadium silicide were identified. The formation of microspherulite calcites most likely occurred in the reducing conditions of the lagoon with high salinity in the contact zone of carbonate and microbial muds. The activation of authigenic mineral formation was facilitated by gas-fluid seeps from an active ancient mud volcano.

Keywords: pelitomorphic matrix, microspherulites, mineralized biofilms, authigenic mineral formation, gas-fluid seeps, Kazantip paleovolcano.

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DOI: 10.19110/geov.2023.11.4

The article presents results of the distribution of the isotopic composition of ¹³C and ¹⁸O (119 samples) across four facies zones to substantiate the conditions of Famennian carbonation accumulation. The Lower Famennian carbonates of the shoal zone showed values of d¹³C (1.5 ± 0.15 %), d¹⁸O (25.01 ± 0.29 %) reflecting evaporative processes in a shallow basin in a warm and dry climate. For the rocks of the microbial mounds zone, the values of d¹³C (2.47 ± 1.12 %) and d¹⁸O (23.51 ± 1.12 %) reflect an increase in bioproductivity and some fluctuation in water salinity. In the limestones of the zone of transition to depression, the variations of isotopic composition are more distinct in the section. Thus, the Early Famennian is characterized by the average values of d¹³C (0.94 ± 0.59 %) and d¹⁸O (23.73 ± 2.18 %) for marine carbonates. The transition to the Middle Famennian is accompanied by isotopic weighting of ¹³C (1.30 ± 0.47%) and ¹⁸O (24.52 ± 1.45%), which shows an increase in evaporation processes under aridization conditions. In the Late Famennian, the isotopic composition abruptly lightens by ¹³C (–1.05 ± 0.66 %), which is associated with desalination under conditions of climate humidification. At the same time, the value of d¹⁸O (25.75 ± 0.31 %) corresponds to the average values for carbonates of the Devonian. The values of d¹³C (1.04 ± 0.89 %) and d¹⁸O (26.01 ± 0.99 %) in the carbonates of the zone slope of the carbonate bank towards the shallow shelf reflect the conditions of the normal sea basin with a slight increase in the evaporation regime during climate aridization. The obtained results indicate that the Famennian sedimentation basin characterized by fluctuations in sea level, facies, water hydrochemistry and climate.

Keywords: Khoreyver Depression, carbonate bank, Famennian, facies zones, paragenetic association carbonate rocks, carbon isotope, oxygen isotope.

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DOI: 10.19110/geov.2023.11.5

The latest most detailed geological map of the Upper Pechora transverse subsidence, compiled by V. V. Yudin, shows an undisturbed western wing passing into the centricline of the Kosyu-Un’ya syncline, composed of Middle Ordovician and Silurian deposits falling to the southeast in the area of the middle course of the Ilych River (from the mouth of the Shezhimyu River to Anna-Di Island). Detailed studies of the sections uncovered in this area, as well as analysis of the literary and field materials of the predecessors, allowed updating ideas about the stratigraphic confinement of some strata and the structure of the area as in general. According to our data, deposits from the Middle Ordovician to the Ludlov unit of the Silurian are revealed within the northern centricline of the Kos’yu-Un’ya syncline, which are divided into three block scales (Shezhimdisk, Mikolael and Ust’Bol’shekosyu), bounded by faults with a plane of incidence inclined to the east-southeast at angles of 30—40°. Tectonic confinement of the complexly dislocated Lower Devonian sediments of the Valgan formation observed at the northern centricline of the fold to the east of the mouth of the Kos’yu River and previously referred to the eastern wing of the Kos’yu-Un’ya syncline, is currently being discussed. According to their lithological composition, they belong to the Shantym facies complex and are probably already part of another tectonic structure — the Valgan «monocline» of the eastern subzone of the Upper Pechora transverse subsidence.

Keywords: Ordovician, Silurian, Devonian, Kos’yu-Un’ya syncline, Ilych River, Northern Urals.

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