Evolution of valley ecosystems of the Bom River (middle Amur River region) in the Late Neopleistocene (MIS 3)
P.S. BELYANIN1, G.S. MIRZEKHANOV2, V.V. IVANOV3
1Pacific Institute of Geography, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia
2Mining Institute, Far Eastern Branch, Russian Academy of Sciences, Khabarovsk, Russia
3Far East Geological Institute, Far Eastern Branch, Russian Academy of Sciences, Vladivostok, Russia
Keywords: Unya-Bom gold-bearing region, palynological analysis, radiocarbon dating, Karginsky megastadial, climatic optimum, paleovegetation
Abstract
The evolution of valley ecosystems of the Bom River (middle Amur River region) has been reconstructed over several climatic cycles of the Late Pleistocene, corresponding to the marine oxygen isotope stage (MIS) 3. The results of the spore-pollen analysis of peat and loam samples from a section of the first floodplain terrace of the Bom River, supported by radiocarbon dating of wood remains and peat, revealed evidence of repeated and significant changes in valley vegetation during climatic fluctuations of the first half of MIS 3. It was found that the warming that started at the beginning of MIS 3 caused the development of spruce-birch forests with Scots pine and alder in the valley. It has been revealed that, apparently, the forest-tundra plant formations, dominated by alder shrubs, shrub and arborescent birches, alder, and larch, which predominated during the preceding, colder era, have shifted higher up the slopes. During the climatic optimum of MIS 3, tree vegetation in the Bom River valley became even more widespread. The main ecosystems of the lower slopes were represented by spruce-small-leaved forests with Scots pine, as well as broad-leaved species such as elm, Mongolian oak and hazel. However, in the swampy areas of the valley, larch sparse forests and sphagnum bogs with dwarf birch and shrubby alder persisted. The process of sedimentation of loams and peat rich in pollen and spores was interrupted during the formation of a thick (7,2 m) layer of boulders and rubble. Significant changes in the taxonomic composition of the palynospectra and the complex lithological structure of the studied section, including transitions from alluvial and biogenic sediments to coarse-grained deposits, indicate significant changes in the natural environment in the Bom River valley during the Late Quaternary.
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