The evolution of the palinocomplexes for alluvial formation sediments of the Baikal Rift Zone in the Neogene

Abstract

Introduction: Currently the issue of identifying stratigraphic units in sedimentary deposits of the Neogene Period in the territory of the Baikal Rift Zone is not completely resolved. To settle this issue we need to compare the results of palynological research of the sediments of the late Cenozoic of the Eastern Sayan and the southern coast of the Baikal Lake and systematize them within the chronological line of the Paleogene and the Neogene. Methodology: All samples were processed in accordance with Grinchuk’s separation method, which includes: treatment with 10% hydrochloric acid (HCl), alkali (NaOH), fluoric acid (HF), and heavy liquid (KJ+CdJ+H 2O). After enrichment the macerate can be seen under a microscope with х400-х600 magnification. The affiliation of spores and pollen to sections, genera, and species was determined by the attributes of the morphological structure of exine, intine, aperture apparatus, pores, and the presence of furrows. Results and discussion: The described palynological material of the deposits of lacustrine-alluvial formation of the southern coast of Baikal and sedimentary formations concealed under the basalts of the Tissa series in the territory of the Eastern Sayan was compared to the data from the stratotype sections of the neighbouring regions. This allowed us to substantiate the correspondence of the obtained data with the stratigraphic boundaries of the regional scheme of the Neogene. During the Eocene angiosperms prevailed in the general composition of pollen. The last stage of the Oligocene is characterized by the domination of gymnosperms, In the lower Miocene the pollen of gymnosperms prevailed as well, but in contrast to the Oligocene, the amount of angiosperm pollen increased. The wide variety of either angiosperm and gymnosperm pollen is typical for the middle Miocene. During the Pliocene the pollen of gymnosperms prevailed. Conclusion: The detailed analysis of the composition of palynocomplexes allowed us for the first time to identify the presence of the Paleogene system deposits in this territory and to organize the spore-pollen complexes of the Neogene in chronological order. On the basis of the palynological research in the Baikal Rift Zone the chronological boundaries of the Tissa series were defined within the context of the Miocene and the lower Pliocene. The age limits of stages and suites of lacustrine-alluvial formation of the southern coast of Baikal within the boundaries of the upper Eocene and the lower Pliocene were also defined.