ABSTRACT A petrological-chronological investigation of the Hindoli Group of rocks within the Jahazpur Shear Zone in the eastern segment of the Aravalli Delhi Fold Belt (ADFB), NW India, has been conducted. We infer two stages of deformation (D1 and D2) and metamorphism (M1 and M2) for the garnet - muscovite - biotiteschists interleaved with meta dolomite, Banded Iron Formation (BIF) amphibolite, and foliated granite. The D2 deformation corresponds to the northeast-trending Jahazpur shear zone on a regional scale. Garnet porphyroblasts, syntectonic with the D2 deformation, are chemically zoned with spessartine-rich cores. Geothermobarometry and pseudosection analyses yield peak P-T conditions of ~7.5 kbar, 580°C, followed by decompression and cooling along a clockwise P-T path. The Sm-Nd isotope analysis of the whole rock yields a date of ~3.0 Ga from an amphibolite. This data is interpreted as the age of formation of the litho-units of the Hindoli Group. Sm-Nd analyses of garnet grains yield an age of ~957 Ma. This date corresponds with the age of nucleation of the Jahazpur shear zone. A good correlation is established between the Neoproterozoic crustal segments of the Jiangnan Fold Belt of the South China Craton and that of the ADFB during the formation of the Rodinia Supercontinent.

An Erratum to this paper has been published: https://doi.org/10.1134/S0016702923210036

The current study was focused on Fe oxyhydroxides from the north-western part of the East-European platform. Modern-day Fe oxyhydroxides of bacterial origin demonstrate an enhanced concentration of rare earth elements (up to 1200 ppm), compared to samples without iron bacteria. The 143 Nd/ 144 Nd ratio in bacterial Fe oxyhydroxide has the value from 0.511532 to 0.512588 and corresponds to the geochemical signature of the waters, oxyhydroxides precipitated from. Samples of iron hydroxides from Quaternary and recent continental ore deposits with different Nd and Sr isotope composition were used for the laboratory reduction of Fe 3+ up to emergence of magnetite ( T ~ 1000°C). 143 Nd/ 144 Nd and 87 Sr/ 86 Sr ratios in the newly formed mineral phases show insignificant discrepancy with parent iron ore. The persistency of Sm–Nd and Rb–Sr isotope systems in the process of bog iron ore experimental melting permits it’s applying to paleoenvironment reconstructions and archaeometry.

The distribution of gold in biogenic apatites from the Ordovician deposits in the northwest of the East European Platform shows that the maximum concentration of gold in apatites is found within the Ladoga-Baltic suture zone. Gold mineralization has a superimposed character, which is confirmed by the dependence of the gold content on the size of apatite particles and a number of isotope geochemical systematics in biogenic apatites. Gold is present in the form of high fineness particles to 20 µm in size on the surface of biogenic apatite fragments (phosphate brachiopod shells and conodont elements) and is easily extracted. In 10 % of samples of biogenic apatites, the total content of rare earth elements is more than 1 wt.%.

Precambrian paleoweathering profiles provide insight into environmental changes and mark stratigraphic boundaries. However, the well-preserved and exposed stratigraphic boundaries, not affected by tectonics, are rare for the Precambrian. We report sedimentological, geochemical and Sr, C and O isotopic data for the Paleoproterozoic weathering profile in Chapanshary Island on Lake Segozero, Central Karelia, the eastern part of the Fennoscandian Shield. The Chapanshary Island weathering crust contains a unique carbonate caliche, rarely developed on the Archean granite-gneiss basement. The crust laterally grades into carbonate-cemented boulder conglomerate, which is overlain by sedimentary carbonate. The chemical index of alteration (CIA; 60-67) and plagioclase index of alteration (PIA; 53-82) values for the weathering crust correspond to weathered felsic/mafic substrate and to illite and K-rich composition of the regolith. The delta O-18 values of carbonate cement and sedimentary carbonate are highly negative (-22.3 to -17.6 parts per thousand V-PDB). The Sr-87/Sr-86 values of Fe- and Mn-rich carbonate of the regolith, boulder conglomerate cement and sedimentary carbonate are 0.7133 to 0.7242 and are exceptionally high for marine Paleoproterozoic carbonate. The high delta C-13 values (+3.9 to + 5.2 parts per thousand V-PDB) of carbonate cement and sedimentary carbonate indicate deposition during the ca. 2.22-2.06 Ga Lomagundi-Jatuli carbon isotope excursion of the early Paleoproterozoic. The Chapanshary Island weathering profile developed in a terrestrial setting with arid to semi-arid climate ca. 2.2-2.1 Ga ago under atmosphere with high CO2 content. The overlying sedimentary carbonates were deposited in a shallow-water setting (ephemeral ponds and lakes) evolved in the inner part of Fennoscandia.

Распределение содержания золота в биогенных апатитах из отложений ордовика на северо-западе Восточно-Европейской платформы показало, что максимальная концентрация золота в апатитах обнаружена в пределах Ладожско-Балтийской шовной зоны. Золотая минерализация имеет наложенный характер, что подтверждается связью содержания золота с размером частиц апатита и рядом изотопно-геохимических систематик в биогенных апатитах. Золото присутствует в виде частиц высокой пробности размером до 20 мкм на поверхности фрагментов биогенного апатита (раковины фосфатных брахиопод и конодонтовые элементы) и легко экстрагируется. В 10 % проб биогенных апатитов суммарное содержание редкоземельных элементов составляет более 1 мас.%

The discovery of numerous bacterial remains (including those morphologically similar to modern ironbacteria) in the lower Proterozoic red-colored quartzites of Shoksha, Karelia, and Bolshoy Tyuters Island of the Gulf of Finland, indicates a significant role of bacterial communities in the formation of hematite pigment in the studied rocks.

Iron-made artifacts from northwest Russia, including nails, arrowheads, and brackets used in the 13th-19th centuries, have a wide range of Sr and Nd isotopic composition (Sr-87/Sr-86=0.710-0.737 and Nd-143/Nd-144=0.5115-0.5124). Authigenic iron ore sites mined in the region from 10th to 19th centuries preserve a similar range of isotopic compositions, suggesting artifacts retain the Sr and Nd signatures of their parent ores. Analyses of the ores also reveal two broad regions distinguished by their isotopic compositions, with the Precambrian Baltic craton in the northern part of the region having very radiogenic Sr and unradiogenic Nd isotopic compositions (Sr-87/Sr-86 >0.7177 and Nd-143/Nd-144 <0.5119) compared with ores from the Paleozoic sedimentary cover of the East European platform to the south. The recognition of distinct geochemical provinces permits identification of the broad regions from which the various ores were mined, and demonstrates the utility of applying radiogenic isotopic analyses to artifacts and their potential geologic sources.

— The Fe/Co ratio (ppm) in the kerogen from different-aged clastic sediments (Early Proterozoic–Mesozoic) varies from 17 to 4100, and δ 13 C value varies from –14.8 to –32.6‰. The relationship between Fe/Co and δ 13 C is determined by the composition of microbial biota in paleobasins and superimposed metamorphic processes. The kerogen from the Vendian deposits of the East European Platform, containing a large amount of saprophytes and actinomycetes is characterized by the maximum Co concentration. The kerogen from deposits metamorphosed under amphibolite-facies conditions are characterized by the minimal δ 13 C and the maximum Fe/Co ratio values.

In this communication, we report geochemical and Sm-Nd isotope data of Banded Iron Formation (BIF) from Kola-Karelia (Fennoscandian shield), East-European Platform and Bundelkhand craton, N-E India. The BIFs from Kola-Karelia (Algoma type), and Bundelkhand Craton (Algoma type), north-central India, and East-European Platform (Superior type) characterized by alternate domains of quartz-rich and iron-rich layers. Except for magnetite and hematite, orthopyroxene, amphibole, and garnet are the other dominant minerals present the BIF's. The shale-normalized REE spectra of iron-rich layers of Bundelkhand, Kola-Karelia and East European BIFs are similar. The epsilon Nd-[t] for silica-rich layers is higher compared to the iron-rich layers for all studied samples. The higher epsilon Nd-[t] values (around + 5.0) for silica-rich layers from Kola-Karelia, Bundelkhand BIF and East European Platform suggest a juvenile source for silica. The lower epsilon Nd-[t] values ( - 5 to + 2) for iron-rich layers from the same samples implies continental source for the iron. The present study suggests that the sedimentation mechanisms of silica and iron for Algoma as well as Superior types BIFs are similar despite spatial diversity.

Oxygenic photosynthesis fundamentally transformed all major biogeochemical cycles and increased the size and complexity of Earth's biosphere. However, there is still debate about when this metabolism evolved. As oxygenic photosynthesis is the only significant source of O2 at Earth’s surface, O2-sensitive trace element enrichments and isotopic signatures in Archean sedimentary rocks can potentially be used to determine the onset of oxygenic photosynthesis by tracking shifts in the oxidative capacity of Earth’s surface environment. Here, we present an extensive new Archean U isotope record from iron formations, organic-rich shales, and paleosols. Variability in δ238U values gradually increased from Archean to Phanerozoic, consistent with current view of gradual oxidation of Earth’s surface. In addition, statistical analysis on available δ238U data indicates a turning point of δ238U variability at roughly 3.0 billon years ago. We suggest that such a turning point in δ238U variability indicates the initiation of relatively large-scale oxidative weathering of U(IV)-bearing minerals, implying that oxygenic photosynthesis may have evolved before 3.0 billion years ago.

Probable microfossils, presumably of bacterial origin, were found in the banded iron formations of Karelia and the Kola Peninsula. The age of these formations is 2.7–2.8 Ga. Based on the organic carbon content and balance estimations it was established that these banded iron formations were deposited in environments rich in organic matter. Comparative analysis of the morphology of Recent and Neoarchean microorganisms suggests a bacterial origin for some magnetite in the studied quartzites.

Microelement composition of Gallionella sp.-containing bacterial mats from the environs of St. Petersburg and isotope composition of organic carbon, strontium, and neodymium from these mats have been determined. Isotope and microelement systematics of iron oxides of bacterial origin characterize the geochemistry of aquafacies that contain ferrobacteria. Certain pre-Cambrian ferruginous quartzites have a similar composition; therefore, one may assume that bacterial oxidation of iron under continental conditions had occurred upon the formation of ironstone during the Precambrian.

Fossilized cyanobacteria(?) represented by trichomes enclosed in common sheaths were detected in early Proterozoic iron banded formations of the Kursk magnetic anomaly (limonite–martite ores of the Lebedinsky mine and iron banded formations of the Korobkovskoye deposit). These fossils morphologically similar to current representatives of the genus Microcoleus were buried in situ.