COMPREHENSIVE PETROMAGNETIC STUDIES OF LACUSTRINE SEDIMENTS FROM LAKE ORDYNSKOYE (PRE-BAIKAL PERIPHERAL BASIN, EASTERN SIBERIA): APPLICATION FOR PALEOECOLOGICAL RECONSTRUCTIONS
M.A. Krainov 1,2, E.V. Bezrukova 1, A.Yu. Kazansky 2,3, A.A. Shchetnikov 1,2
1Vinogradov Institute of Geochemistry SB RAS, Irkutsk,Russia
2The Institute of the Earth’s Crust SB RAS, Irkutsk, Russia
3Geological Institute RAS, Moscow, Russia
Keywords: Cis-Baikal region, Angarskaya Steppe, Late Holocene, petromagnetism, stratigraphy, lacustrine sedimentation conditions, climate, anthropogenic influence
Abstract
The first reconstruction of lacustrine sedimentation conditions for the extensive territory of the Angara steppe (Pre-Baikal Depression) in the Late Holocene with decadal temporal resolution is presented. The reconstruction is based on the results of a comprehensive study of Lake Ordynskoe sediments: petromagnetic and granulometric parameters, biogenic silica content. Sedimentation rates and the age of the reconstructed events were determined using radioisotope dating (²¹⁰Pb and ¹³⁷Cs). The age of the core base is 2800 cal yr BP. As a result, it is shown that the primary contribution to the magnetization of Lake Ordynskoe sediments, unlike other studied lakes in the region, comes from grains produced by magnetotactic bacteria. Nevertheless, the analysis of the behavior of biogenic magnetization components provided information on the Lake bioproductivity and relative changes in redox conditions during sediment formation at the water-bottom interface, while the results of granulometry were informative for reconstructing relative changes in lake level. Despite this specific feature of the formation of the lake sediment's petromagnetic characteristics, it was established that noticeable anthropogenic influence on the Lake Ordynskoe geosystem began approximately 280 years ago, intensifying significantly in the last century due to the agricultural activity.
|
