RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES6003, doi:10.2205/2005ES000183, 2005
[2] The discovery of hundreds of microfossil localities in the Precambrian sediments demonstrated a complicated differentiation of life that included bacteria forms and groups of algae, fungi, and animal organisms [Martin, 1993; Semikhatov et al., 1999; Jankauskas et al., 1989]. At the same time the major problem of Precambrian microfossil studies is the elucidation of biological affinity of forms from certain localities. The establishment of natural taxonomic affiliation of microfossils is the most topical issue for Neoproterozoic biotas characterized by the greatest diversity of organic remains. Most of forms derived from syngenetic flints of shallow-water biochemogenic carbonates, according to their morphology and environmental conditions, are correlated with confidence with modern cyanobacteria [Sergejev, 1992, 2003; see reference to Knoll et al., 1991]. Organic-walled microfossils extracted using acid from terrigenous rocks are commonly referred to acritarchs (Acritarcha Evitt, 1963), a group of uncertain taxonomic position [Jankauskas et al., 1989]. However, both silicified and most of organic-walled microfossils were mainly studied from shallow-water beds of paleoshelves' littoral and upper sublittoral zones. Microbiotas from deep-water sediments, let alone bathyal zones, are incomparably less known [Akhmedov et al., 2000; Horodyski, 1993; Moorman, 1974]. But even the available scarce records indicate that forms of deep-water biotas differ greatly in morphology and lesser dimensions from well-known shallow-water microfossils. The knowledge of microfossil assemblages in geodynamic aspect is closely similar. Most of the Proterozoic microbiotas were found in the sediments of paleoshelves that represent relics of passive continental margins. Microfossil findings from sedimentary volcanogenic rocks of Proterozoic island-arc environments are scarce. The major reason for poor knowledge of these forms is a scarce preservation of corresponding sediments. Deep-water sediments and geologic bodies of active continental margins experience more or less intense transformation in collision zones and have a low probability to be preserved [Reding, 1990]. These sediments are commonly represented by tectonic fragments of intensely deformed and more or less metamorphized rocks.
[3] Among major lines of microfossil studies the microphytologic correlation is of particular interest. However, on numerous occasions, especially in the initial period of Precambrian microphytology, the chronological inferences from microfossils, lacking a paleontological base, followed the adopted stratigraphic schemes. As new records became available, the microfossils with a sufficiently complicated morphology were recorded and were used for correlation of large stratigraphic units. However, eventually the application of these microscopic and relatively poorly studied remains for correlation implies a comprehensive research permitting the separation of original groups of microorganisms. Having regard to convergent features typical of protozoans and possible affiliation of acritarch forms to different biological groups (up to kingdoms) inhabiting various environments, the use of microfossils for correlation should include records of ecologic and natural taxonomic investigations. The latter results are eventually the components of actuopaleontological correlations that are basic to evolutionary conclusions and therefore to biostratigraphic inferences. This methodical model of classic paleontology is still by far little applicable for heterogeneous assemblages of the Precambrian microremains. However, the available records already permit the attempts to separate microfossil morphotypes in hypothetically related groups.
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Citation: 2005), Precambrian microfossil-characterized biotopes from the southern margin of the Siberian craton, Russ. J. Earth Sci., 7, ES6003, doi:10.2205/2005ES000183.
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