Temporal Compositional Variations of Cenozoic Sediments on the Tankhoi Tectonic Step, the Southern Baikal

The castorid dental material described in this paper derives from Miocene, fossiliferous deposits of the Baikal rift valley, exposed at Tagay Bay on Olkhon Island in the Lake Baikal, in eastern Siberia. It consists of maxillary fragments and isolated upper and lower teeth of the small trogontheriine beaver Euroxenomys minutus (von Meyer, 1838). It is the first record of the species in Asia and at the same time the northernmost occurrence of Eurasian Miocene beavers. The magnetostratigraphic correlation of the Tagay -1 section, indicates a late Burdigalian, Early/early Middle Miocene age of ~16.5 to ~16.3 Ma that corresponds to the Mammalian Neogene zone MN4/5. The presence of E. minutus in Tagay is an indicator for an Orleanian European-Siberian bioprovince during the Mid-Miocene Climate Optimum, and for a continuous belt of humid, warm-temperate to subtropical forests, stretching from Europe to Siberia, and probably further to East and South-Eastern Asia. In Eurasia, beaver remains are an indicator of permanent water bodies, which is in agreement with the palaeoenvironment of the Tagay locality.

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The northernmost Eurasian Miocene beavers: Euroxenomys (Castoridae, Mammalia) from Olkhon Island, Lake Baikal (Eastern Siberia)

Mörs

Hägglund

Erbajeva

et al. 2022

Palaeobio Palaeoenv

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Occurrence of Tankhoy field coals in South Baikal bottom sediments

Khlystov

Vainer-Krotov

Kitaev

et al. 2021

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The purpose of the study is to describe the first finds of coal-bearing clays and coals in the bottom sediments of the southern basin of Lake Baikal and compare them with terrestrial coal-bearing deposits of the Tankhoy field. Comparative analysis of the lithological composition and colour of bottom sediments and terrestrial sections, as well as the concentration of organic carbon and conducted palynological analysis allowed their correlation. At the lake’s depth of 900 m the authors discovered a coal-bearing strata in situ (st 56), which later was stratigraphically correlated with the terrestrial coalbearing part of the Tankhoy suite. The fragments of coal found in bottom sediments basically along the entire Tankhoy field, especially bedrock coals on the underwater slope in South Baikal up to 1300 m deep prove the distribution of the coal-bearing part of the Tankhoy suite in the sublacustrine part of the lake throughout the entire slope (from 5 to 10 km offshore) and confirm the distribution area of the Tankhoy paleolake over a significant area of the contour of modern southern basin of Lake Baikal. The finds of coal-bearing strata on these and other various sub-bottom depths, i.e. under various pressure and temperature conditions, suggest that coals themselves and coal-bearing mudstones may be a generation facility of secondary microbial methane. This should be taken into account when searching for gas hydrocarbon and gas hydrate accumulations as well as assessing methane cycles in Lake Baikal.

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Olivine as an indicator of polygenic assemblage of inclusions from Late Cenozoic volcanic rocks in the Tunka Valley, Baikal Rift Zone

et al. 2021

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Research subject. Olivine of deep-seated inclusions from Late Cenozoic volcanic rocks of the Tunka valley.Materials and methods. Electron probe microanalysis of minerals with determination of calcium in olivine by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). A complex of methods of quantitative chemical analysis for determination of major oxides in rocks.Results. Deep-seated nodules from Late Cenozoic volcanic rocks in the Tunka Valley characterize the root part of the Slyudyanka metamorphic subterrane, formed during collisional accretion of the Khamar-Daban terrane to the Siberian paleocontinent in the Early Paleozoic and reactivated in the Late Cenozoic. From bulk compositions of deep-seated nodules, groups of xenoliths (restites, rocks closed to the primitive mantle composition, and metasomatites) and cognate rocks (magmatic and magmatic-metasomatic genesis) were distinguished. The polygenetic character of this assemblage is designated by variations of major and trace-element abundances in olivine. In olivine of xenoliths, forsterite (Fo) ranges from 86 to 91% under abundances of NiO – 0.2–0.5, MnO – 0.1–0.2, and CaO < 0.16 wt %. In olivine of magmatic rocks and those of mixed (magmatic-metasomatic) genesis, Fo decreases to 64% with a decrease in NiO (Ni/Mg ratio) and an increase in MnO and CaO. Magmatic olivine shows 0.16–0.21 wt % MnO and about 0.1 wt % CaO, in contrast to olivine of magmatic-metasomatic genesis, enriched in these oxides to 0.5 wt % and 0.45 wt %, respectively, with an increase in the Mn/Fe and Ca/Fe ratios. Olivine trends of the shallow polygenetic assemblage of inclusions are emphasized when compared with those of the deeper ones from volcanic rocks of the Vitim and Oka plateaus that represent a transition from the garnet to the spinel-pyroxene facies in mantle peridotites.Conclusion. Olivine compositions are indicative of the shallow origin of peridotite and pyroxenite nodules from the crust and crust–mantle transition in the root part of the Slyudyanka collision zone reactivated in the Late Cenozoic.

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Temporal Compositional Variations of Cenozoic Sediments on the Tankhoi Tectonic Step, the Southern Baikal

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The northernmost Eurasian Miocene beavers: Euroxenomys (Castoridae, Mammalia) from Olkhon Island, Lake Baikal (Eastern Siberia)

The northernmost Eurasian Miocene beavers: Euroxenomys (Castoridae, Mammalia) from Olkhon Island, Lake Baikal (Eastern Siberia)

Occurrence of Tankhoy field coals in South Baikal bottom sediments

Olivine as an indicator of polygenic assemblage of inclusions from Late Cenozoic volcanic rocks in the Tunka Valley, Baikal Rift Zone

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