COMPREHENSIVE PETROMAGNETIC STUDIES OF LACUSTRINE SEDIMENTS FROM LAKE ORDYNSKOE (Baikal peripheral basin, eastern Siberia): APPLICATION FOR PALEOECOLOGICAL RECONSTRUCTIONS
M.A. Krainov1,2, E.V. Bezrukova1, A.Yu. Kazansky2,3, A.A. Shchetnikov1,2
1Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
2Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
3Geological Institute, Russian Academy of Sciences, Moscow, Russia
Keywords: Baikal region, Angara steppe, late Holocene, petromagnetism, stratigraphy, lacustrine sedimentary environment, climate, anthropogenic impact
Abstract
We present the first reconstruction of a lacustrine sedimentary environment for the extensive area of the Angara steppe (Baikal peripheral basin) in the late Holocene with decadal temporal resolution. The reconstruction is based on the results of a comprehensive study of lacustrine sediments from Lake Ordynskoe: petromagnetic and granulometric parameters and biogenic silica content. We have determined sedimentation rates and the age of the reconstructed events using radioisotope dating (²¹⁰Pb and ¹³⁷Cs). The age of the core base is 2800 cal yr BP. The results show that the primary contribution to the magnetization of sediments from Lake Ordynskoe, unlike other studied lakes in the region, comes from grains produced by magnetotactic bacteria. However, the behavior analysis of biogenic components of magnetization provides information on the lake bioproductivity and relative changes in redox conditions during the formation of sediments at the water-sediment interface, and the results of granulometry are informative for reconstructing relative changes in the lake level. Despite this particularity in the formation of the lake’s petromagnetic sediments, we have established that noticeable anthropogenic impact on the geosystem of Lake Ordynskoe began approximately 280 years ago, significantly increasing in the last century due to agricultural activity.
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