Principal stages in evolution of Precambrian organic world: Communication 1. Archean and Early Proterozoic

Expounded in this work are the results of critical consideration of published and original data on biologic nature and appearance chronology of different groups of Archean and Lower Proterozoic (3.5–1.65 Ga) paleontological remains known from geological record. Conclusions are substantiated by morphological analysis of structurally preserved microfossils, their facies distribution, and by inferable genesis and principal evolutionary trends of Archean stromatolites. A special attention is paid to variations of organic and carbonate carbon isotope composition in sedimentary successions with paleontological remains and to recent information about discovered, most ancient biomarkers of large groups of organic world. As a result of this approach, a detailed model of Precambrian organic world evolution is suggested.     

Eukaryotization of the early biosphere: A biogeochemical aspect

The synthesis of data on the paleobiology and geochemistry of the Archean and Proterozoic and the ecology, biochemistry, and comparative genomics of living organisms provides a means for reconstructing the development of biological complexity on the subcell, organism, and ecosystem levels. The conditions and time of the origin of oxygenic photosynthesis, eukaryotic cells, and multicellular animals were determined. These evolutionary events had a profound influence on the global biogeochemical cycles, sedimentogenesis, and climate of the Earth. Irreversible geochemical changes in the biosphere and the biochemical evolution of living systems are described as complementary processes. A decrease in hydrogen concentration in the early biosphere, an increase in oxygen concentration in the ocean, and changes in the bioavailability of metals (Fe, Ni, Co, V, W, Cu, Mo, etc.) known as enzyme activators were considered as key factors of eukaryotization. The reasons for variations in the availability of the metals in the biosphere were distinguished. The continuity of life was maintained owing to the preservation of the functionality of archaic metabolism types through the compartmentalization of biochemical reactions and the complication of cellular metabolic networks. The metabolic cascades of living cells probably recapitulate this prolonged evolutionary process. The exhaustion of abiogenic hydrogen sources stimulated the symbiosis of hydrogen-producing and hydrogen-consuming prokaryotes and the involvement of simple hydrogen-bearing volatile compounds (CH₄, NH₃, H₂S, and, finally, H₂O) as a substrate for life, which eventually predefined the chemical composition of the terrestrial atmosphere strongly dominated by nitrogen and oxygen as by-products of exchange reactions. The oxygenation of the ocean diminished the mobility and bioavailability of some metals that had served as the earliest enzyme activators. The evolutionary response to this process was the formation of mechanisms of extraction, accumulation, and the retention of ancient activator metals (e.g., Fe, W, and Ni) in the cell and in the ecosystem, as well as the active involvement of new metals (e.g., Mo, Cu, and Zn). Oceanic biota became the main concentrator and reservoir for these metals. The appearance of eukaryotic cells, the increasing role of heterotrophy, an increase in biodiversity, the complication of trophic relationships, the acceleration of the cycle of biophile elements, and other features of the biosphere eukaryotization were to large extent a response to the narrowing of the geochemical basis of life. A pivotal point in the prolonged process of biosphere eukaryotization was a series of glaciations at the end of the Proterozoic (750–540 Ma) and the active oxygenation of the ocean, which enabled the global expansion of eukaryotic organisms.     

New data on the geological structure of the southwestern Mendeleev Rise,Arctic Ocean

This communication considers the ideas about the geological structure of the southwestern Mendeleev Rise belonging to the East Arctic rises of the Arctic Ocean. These ideas have resulted from analyzing the data obtained from bathymetric surveys, visual observations, and bottom coring using the technical tools of a research submarine. We distinguished the lower sequence of quartzite sandstones and dolomites, which has a visible thickness of about 230 m and occurs in the lowermost visible section, at depths between 1500 and 1270 m. This sequence is superimposed with stratigraphic and angular unconformity by the upper sequence of limestones and sandstones having a visible thickness of 40 m. The lower sequence is pierced by subvolcanic rocks of basaltic to andesitic composition, and in the lowermost part of the slope, a tuffaceous sequence having a visible thickness of 50 m adjoins it.     

The first magnetostratigraphic data on the stratotype of the Lopata Formation,Northeastern Yenisei Ridge: Problems of its age and paleogeography of the Siberian Platform at the Proterozoic–Phanerozoic boundary

New paleomagnetic and magnetostratigraphic data are presented for the stratotype of the Upper Riphean Lopata Formation (Teya River, Yenisei Ridge). The paleomagnetic pole calculated is significantly distinct from the Phanerozoic and Riphean poles of the Siberian Platform and is similar to the Late Vendian–Early Cambrian poles of the Madagascar Group. The stratigraphic range studied is characterized by an anomalously high frequency of geomagnetic inversions (15 zones of magnetic polarity), which is comparable with the inversion frequency of the Late Vendian sections of Baltica. These data, along with previous paleontological findings, indicate an age of the Lopata Formation of 555–540 Ma.     

Palaeopascichnids from the Upper Vendian Chernyi Kamen Formation of the Middle Urals (Perm Region)

Doklady Earth Sciences - In 2020–2021 the palaeopascichnid fossils were found in the Krasnaya Gorka Site (Shirokovsky Reservoir, Kosva River area, Perm Region), a type Vendian fossil locality...     

Principal stages in evolution of precambrian organic world: Communication 2. The late proterozoic

A new suggested model outlining the evolution of the organic world from the mid-Early Proterozoic (∼2.0 Ga) to the Early Cambrian is based on data characterizing the relevant chert-embedded and compression-preserved organic-walled microbiotas, impressions of soft-bodied multicellular organisms, and biomarkers. Critical analysis of overall paleontological data resulted in the distinguishing of seven successive assemblages of Proterozoic micro- and macrofossils. Being of global geographic range, the assemblages correspond to the major stages in evolution of the organic world and typify global units which are termed the Labradorian (∼2.0–1.65 Ga), Anabarian (1.65–1.2 Ga), Turukhanian (1.2–1.03 Ga), Uchuromayan (1.03–0.85 Ga), Yuzhnouralian (0.85–0.635 Ga), Amadeusian (0.635–0.56 Ga), and Belomorian (0.56–0.535 Ga). Characteristic of the Labradorian unit are microfossil assemblages of the Gunflint type including remains of morphologically bizarre prokaryotic microorganisms: star-like Eoastrion, umbrella-shaped Kakabekia, dumbbell-shaped Xenothrix, and some others. Fine-grained siliciclastic deposits of the same age yield the oldest remains of millimeter-sized eukaryotes: spherical to ribbon-like Chuaria and Tawuia. Microfossils prevailing in shallow-water carbonate facies of the Anabarian unit are akinetes of nostocalean cyanophyceae Archaeoellipsoides and entophysalidacean cyanobacteria Eoentophysalis, whereas acanthomorphic acritarchs Tappania and Shuiyousphaeridium dominate the assemblages of open-shelf facies, where they are associated with the first-found rare macroscopic multicellular fossils Horodyskia. The distinguishing feature of the next Turukhanian unit is the first occurrence of filamentous red alga Bangiomorpha and the stalked cyanobacterium Polybessurus. The Uchuromayan unit is characterized by the appearance and worldwide radiation of structurally complicated eukaryotic microorganisms, primarily of acanthomorphic acritarchs Trachyhystrichosphaera and Prolatoforma, branching thalli of green algae Aimophyton, Palaeosiphonella, Palaeovaucheria and Proterocladus, and of spiral-cylindrical cyanobacteria Obruchevella. In the Yuzhnouralian unit is recorded the first occurrence of vase-shaped testate amoebas Melanocyrillium, Cycliocyrillium, and others, and of scale microfossils Characodictyon, Paleohexadictyon, etc. As distinct from the others, the Amadeusian unit characterizes the global expansion of acanthomorphic acritarchs of complex structure (the Pertatataka-like assemblage of Tanarium, Cavaspina, Appendisphaera, and others) and associated remains of red algae and cyanobacteria Obruchevella. The terminal Belomorian unit marks the extinction of Pertatataka-type microfossils, the appearance of soft-bodied multicellular organisms on different continents, and the origin of diverse skeletal fossils in the terminal phase.     

Hydrocarbon Potential of Paleo- and Modern Suprasubduction Provinces: Tectonic,Geodynamic, Mineralogical-Geochemical,and Biochemical Aspects

The paper is devoted to the integrated analysis of the interdisciplinary problem of the genesis of hydrocarbon potential in suprasubduction provinces. A geodynamic model is proposed for the formation of petroleum pools on the shelves of the Meso-Cenozoic back-arc basins in the western Pacific Ocean. Original data on the tectonics and composition of the mantle peridotites of the Polar Ural ophiolite complexes are given for comparison. These data are used to consider the low-temperature lizardite–chrysotile and high-temperature antigorite types of peridotite serpentinization in the back-arc basins and in the mantle wedges above the subduction zones of the paleozoic Paleouralian ocean. It is established that these processes are responsible for the abiogenic synthesis of hydrogen and methane. Of great theoretical and applied importance are the conclusions concerning the high antiquity of serpentinization as a hydrogen source, the possible relationships of the origin of life and its early evolution with hydrogen emission in the benthal, the predominance of chemoautotrophic prokaryotes with hydrogen exchange among the primary producers of organic matter in anaerobic conditions, and the high probability of naphthidogenesis based on the prokaryotic communities in the Archean and Proterozoic. The origin of hydrocarbons in the framework of the considered model is regarded from a viewpoint of a polygenetic paradigm of oil and gas generation.