Holocene environmental conditions in the Eastern Sayan foothills according to a comprehensive paleoecological study of the Sosnovka mire

Abstract

This research is devoted to the study of the combined vegetation dynamics, hydroclimatic conditions and fires in the foothills of the Eastern Sayan northwestern macroslope in the Holocene. The paleoecological reconstruction results obtained on the basis of AMS-dating, pollen, macrofossils, charcoal and malacofaunal analysis of peat deposits of the Sosnovka mire (right bank of the Yenisei River), covering the last ≈11,000 calendar years are presented. It was established that the process of waterlogging began at ≈9700-8500 cal yr BP at the optimum heat and moisture, when the waterless valley were covered with a mixed siberian pine-spruce-fir forest, with the maximum participation of spruce and fir. According to the study of Sosnovka mire sediments the reaction of local and regional communities to the Holocene Thermal Maximum (7500-6000 years ago) was clearly manifested. The participation of spruce and fir in the trees layer stand decreased sharply. The increase in fire activity was noted, which contributed to the lightening of forests and greater development of the shrub layer. During this interval, the process of swamping actively began in the floodplains of rivers with a drainage area in the western part of the Eastern Sayan. Based on the results of charcoal analysis six stages of increased fire activity were identified: I – about 10,000-8,800 cal yr BP, II – 7500-7200, III – 5600-5000, IV – 3700-3000, V – 2100-1800, VI – 800 cal yr BP - until now.