Reconstruction of the geochemical evolution of the saline lake Shira (Southern Siberia, Russia) in the late Holocene

Abstract

The paper presents reconstruction of the geochemical evolution of the saline lake Shira (South Siberia, Russia) over the past 3000 years based on the elemental composition of bottom sediments. Based on the rock-forming element contents obtained by X-ray fluorescence analysis, the main geochemical indices were calculated to assess the degree of deformation and weathering of the rocks in the catchment basin, paleosalinity, paleoclimate, paleoproductivity and input of clastic materials. Changes in Al₂O₃ and TiO₂ contents reflect the influence of the terrigenous contribution in the lake basin and demonstrate four decreases in the terrigenous removal contribution in the age intervals of 40-135, 580-800, 1900-2020 and 2780-2850 cal. a BP. These intervals are characterized by decreases of Na₂O, SiO₂, K₂O and Fe₂O₃ contents and increases of MgO and CaO contents. The deceleration in the processes of physical weathering of terrigenous material from banks into the lake and its removal by watercourses is confirmed by the increase of the paleosalinity index and the decrease of chemical weathering. The four considered intervals are characterized by high values of the Ti/Zr ratio, which corresponds to rocks formed close to the provenance area. For the interval 2780-2850 cal. a BP, the change of the Ti/Zr ratio value is not so contrasting in comparison to the intervals 40-135, 580-800 and 1900-2020 cal. a BP. The mineral composition of the bottom sediments of saline lake Shira corresponds to young and immature clay mineral with a high percentage of primary silicate minerals, formed under cold climate conditions.