ANALYSIS OF FLORA AND CLIMATE IN WEST SIBERIA AT THE EARLY-LATE PLIOCENE AND PLIOCENE-EOPLEISTOCENE BORDERS

On the basis of palinological and carpological analyses, the compositi on of flora from deposits dated to the second half of the Early Plioce ne (Bitekei horizon, 4-3.4 Ma ago), Late Pliocene (3.4-2 Ma ago), and Eopleistocene is described. It is shown that progressing climate cooli ng was accompanied by a gradual change in the composition of flora and plant communities. The flora composition and plant formations at the end of the Early Pliocene (Bitekei stage) differed from the modern one s. They indicate a significantly warmer climate, with the annual avera ge temperatures being up to 10 degrees C higher than the present-day o nes. At the beginning of the Late Pliocene (Seletinian stage) the clim ate was still warm. It favored an origin of broad-leaved plants in the south of West Siberia. Significant changes of flora and climate took place in the second half of the Late Pleistocene tend of the Barnaul s tage), about 2 Ma ago. By that time, most of the modern plants, includ ing hypoarctic ones (bush-like birch, lycopods), had already appeared. This period is involved with dispersal of dark conifers over the terr itory of the West-Siberian forest-steppe zone.; The progressing climat e cooling, which reached its maximum by the beginning of the Eopleisto cene, gave rise to new species and communities. At the beginning of th e Eopleistocene (1.8-1.6 Ma ago, Erestninian and Ubinian stages), new plant formations having no analogs among the modern formations origina ted. In the forest-steppe zone dark-conifer formations, bog-tundras, a nd bog-steppes appeared. The climate was close to the modern forest-st eppe climate, with the annual average temperatures being 11 degrees C lower than the present-day ones. Analysis of the flora has shown that the above time interval corresponds to the most significant climatic c hanges and may be the most reasonable for determining the lower time b oundary between the Neogene and Quaternary.