ISSN 2078-502X Published by the Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences GEODYNAMICS & TECTONOPHYSICS PALEOGEODYNAMICS DOI: 10.5800/GT-2020-11-2-0473 2020 VOLUME 11 ISSUE 2 PAGES 262–284 262 https://www.gt-crust.ru RESEARCH ARTICLE Received: August 21, 2019 Revised: November 29, 2019 Accepted: December 04, 2019 FOR CITATION: Hassan A., Rasskazov S.V., Chuvashova I.S., Yasnygina T.A., Titova L.A., Kulagina N.V., Usoltseva M.V., 2020. Identifying Upper Miocene – Lower Pliocene lacustrine sediments in dry Tunka basin of the Baikal rift zone. Geodynamics & Tectonophysics 11 (2), 262–284. doi:10.5800/GT-2020-11-2-0473 IDENTIFYING UPPER MIOCENE – LOWER PLIOCENE LACUSTRINE SEDIMENTS IN DRY TUNKA BASIN OF THE BAIKAL RIFT ZONE A. Hassan 1,2 , S.V. Rasskazov 1,3 , I.S. Chuvashova 1,3 , T.A. Yasnygina 3 , L.A. Titova 4 , N.V. Kulagina 3 , M.V. Usoltseva 4 1 Irkutsk State University, Irkutsk, Russia 2 Al-Baath University, Homs, Syria 3 Institute of the Earth’s Crust, Siberian Branch of RAS, Irkutsk, Russia 4 Limnological Institute, Siberian Branch of RAS, Irkutsk, Russia ABSTRACT. We present results of lithogeochemical, diatomic and palynological studies of sediments from the Tunka-13 well that was drilled in the southeastern part of dry Tunka basin in the Baikal rift zone. At the base of the section, there is an eroded basaltic flow of 16–15 Ma. From lithogeochemical signatures, we identify nine sedimentary units. The seven lower ones (interval 7.2–86.5 m) belong to the Tankhoi formation, the eighth (interval 2.7–6.6 m) to the Anosov formation, the ninth (interval <2.4 m) to the sandy stratum. We determined local sources of clastic material of basaltic and silicic compositions for units 1 and 2, respectively, and remote sources of silicic compositions for the overlaying units. The section shows a change from alluvial facies (units 1–3) through avandelta (unit 4) and lacustrine ones (units 5–7), again to alluvial facies (unit 8) and then to lacustrine-eolian ones (unit 9). Spore and pollen spectra from sediments of units 1–7 are divided into three palynozones (PZ), reflecting the vegetation change in the Late Miocene – Early Pliocene: PZ-1 – coniferous and deciduous forests with a small participation of thermophilic broadleaved species in moderately warm, humid climatic conditions; PZ-2 – enhancing the role of hemlock and more diverse thermophilic deciduous rocks in more humid and warm conditions; PZ-3 – a gradual reduction in the number of hemlock and other dark coniferous species, removing broad- leaved species by birch and alder, growing grassy communities in wetlands due to climate cooling. We identified layers of lacustrine facies by occurrence of fossil diatoms that are absent in the layers of the alluvial and avandelta facies. In lacustrine sediments, we distinguish four diatom zones: DZ-1 denotes a relatively deep Late Miocene paleolake, marked by planktonic species, DZ-2, DZ-3 and DZ-4 – a shallow Early Pliocene lake with a developed littoral zone and short transgression. The Late-Miocene paleolake transgression, indicated by changing facies, is associated with structural reorganization, accompanied by volcanic extinction in the Tunka valley about 9–8 Ma, and the Early Pliocene short transgression with a new reorganization, reflected in volcanic rejuvenation about 4.0 Ma. KEYWORDS: Baikal; Tunka basin; sediments; volcanism; Miocene; Pliocene; stratigraphy; lithogeochemistry; diatom analysis; palynological analysis FUNDING: The study was carried out under the state assignments of the Geological Faculty of the Irkutsk State University, Institute of the Earth’s Crust SB RAS (No. 0346-2016-0005), and the Limnological Institute SB RAS (No. 0345-2019-0001) and supported by RFBR (projects 19-04-00746 and 18-35-00417 mol_a). Drilling of the Tunka-13 well was funded by RFBR.