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Age Boundaries and Stratigraphic Importance of Microbiota of the Lower Riphean Kaltasy Formation of the Volga–Uralia Area
Stratigraphy and Geological Correlation ( IF 1.0 ) Pub Date : 2019-09-30 , DOI: 10.1134/s0869593819050071 V. N. Sergeev , M. A. Semikhatov , N. G. Vorob’eva , N. D. Sergeeva , M. Sharma , L. P. Baryshnikova
中文翻译:
伏尔加河-乌拉利亚地区下里phean Kaltasy组微生物群落的年龄边界和地层学重要性
更新日期:2019-09-30
Stratigraphy and Geological Correlation ( IF 1.0 ) Pub Date : 2019-09-30 , DOI: 10.1134/s0869593819050071 V. N. Sergeev , M. A. Semikhatov , N. G. Vorob’eva , N. D. Sergeeva , M. Sharma , L. P. Baryshnikova
Abstract
The association of organic-walled microfossils of the Kaltasy Formation, which includes morphologically complex large forms, is considered on the basis of previous and new materials. In general, the Kaltasy microbiota is similar to many associations of the Neoproterozoic (Late Riphean and Vendian) microfossils and, originally, was erroneously interpreted as Late Riphean, in spite of missing Late Riphean index taxa and geological evidence of its Early Riphean age. The Early Riphean age of the formation was supported by results of Re–Os, U–Pb, and other modern methods of isotope geochronology, whereas the low 87Sr/86Sr ratios and almost invariant δ13C values of its rocks are comparable with isotopic characteristics of the Mesoproterozoic sequences of >1300 Ma. The application of geochemical methods using high-reagent Fe (FeHR) and C and S isotopes has showed that relatively deep rocks of the Arlan Subformation of the Kaltasy Formation accumulated under aerobic oxidation conditions (ratio FeHR/FeT < 0.38). This contradicts a common concept of the presence of an anoxic ocean in the Mezoproterozoic, but explains the presence of morphologically complex large eukaryotic forms of microbiota, which were abundant in Neoproterozoic oxygenic basins.中文翻译:
伏尔加河-乌拉利亚地区下里phean Kaltasy组微生物群落的年龄边界和地层学重要性