PALYNOLOGICAL AND DIATOM ANALYSES OF SEDIMENTS FROM THE LATE CENOZOIC PALEO-AMALAT VALLEY (Western Transbaikalia)
S. V. Rasskazov, N. A. Logachev, A. V. Ivanov, V. A. Misharina, G. P. Chernyaeva, I. S. Brandt, S. B. Brandt, V. M. Skoblo, and N. A. Lyamina
Keywords: Central Asia, Late Cenozoic, sediments, basalts, spore, pollen, diatoms
Pages: 773-785
Abstract
Sections of interlayered sediments and basaltic lavas have been studied in drill cores from the eroded valley of the paleo-Amalat River and its tributaries. Deposition in the valley started in the Middle Miocene about 14 Ma ago and ceased in mid-Quaternary time about 0.6 Ma ago. Palynologic and diatom age constraints of the sediments are in line with K-Ar dating of volcanics. The composition of diatoms attests to repeated appearance and drying of deep lakes between 14 and 9 Ma ago.
A factor analysis of spore and pollen spectra in the sediments shows a two-stage evolution of vegetation on the Vitim plateau in the Late Cenozoic: (1) progressive changes of Miocene Turgai-type flora in a warm humid climate between 14 and 9 Ma ago and (2) transition to Boreal flora under sharp cooling and aridization since 9-5 Ma ago. The two stages generally correspond to similar evolution stages of the flora in southeastern East Sayan. The Miocene flora in the territory between Northern Baikal and southeastern East Sayan differed from that on the Vitim plateau. These differences gradually disappeared since the Late Miocene, whereas the flora of southeastern East Sayan still preserved its specific features.
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