Weathering in the Lake Baikal watershed during the Kazantsevo (Eemian) interglacial: Evidence from the lacustrine clay record

Abstract

Abstract:The clay-mineralogical record of a piston core recovered on an elevated plateau in the northern basin of Lake Baikal has been investigated for the Kazantsevo interglacial period (i.e., Eemian s.s. equivalent in northern Europe). The age model (as inferred from palaeomagnetic intensity) suggests that this stage spans ca. 128 to 117 kyr BP. Relative clay mineral abundances and clay-mineral ratios are used to reconstruct the weathering conditions within the Baikal watershed at a sub-millennial resolution, and suggest that the clay record is highly variable. A bimodal clay-data distribution is in agreement with different clay sources and/or formation between the studied glacial and interglacial periods. High amounts of smectites in the Taz glacial samples (128.7-136.4 kyr BP) may be explained by an additional source of neoformed smectites during the glacial stage. In addition to the classically used smectite/illite ratio, the mineralogical results are integrated by the calculation of a hydrolysis index that takes into account the abundance of all clay species and their sensitivity to chemical weathering. A principal components analysis (PCA) of the Baikal clay minerals allows the comparison of the clay parameters with regard to weathering conditions. Clay data are further compared (i) with diatom and pollen profiles, (ii) with pollen-based quantitative reconstructions for the same core material, and (iii) with other climate reconstructions for the Lake Baikal region and Siberia. Several features of our record are highlighted here. During the early period of the Kazantsevo interglacial (128.4-125.2 kyr BP), weathering processes remain controlled by physical reworking for more than 2 kyr after the initial transition from cold to warm conditions. Inception of chemical weathering starts only after ca. 125 kyr BP, a period coincident with the warmest conditions according to both the pollen record and by the strongest chernozem development in Siberian soils. Within the interglacial interval, the hydrolysis index displays a two-step increase, punctuated by a minimum value ca. 122 kyr BP. The increasing but irregular trend persists after the transition from the Kazantsevo interglacial to the Zyryanka glacial (~ 117 kyr BP). Peak chemical weathering, as inferred by clay changes, lags the interglacial/ glacial transition by at least 2 kyr. This suggests that pedogenesis remains active after the interval of surface stabilization. Lake Baikal clay minerals trace the nature of the main weathering conditions within the watershed. We note any increase in physical weathering is rapidly recorded in sedimentary clay assemblages but the mineral imprint to chemical weathering changes is more gradual, lagging reconstructed climate conditions over the lake by ca. 2 kyr.

Changes of Water Level in the Eemian Palaeolake at Imbramowice (SW Poland) Based on Isotopic and Cladoceran Data

“…Furthermore, the positive correlation of δ 18 O and δ 13 C curves suggests the lake operated as a closed system throughout most of its Eemian history. A hypothesis about occurrence of short-time cooling during mid-Eemian (Cheddadi et al, 1998;Granoszewski et al, 2005;Fagel and Mackay, 2008) is not reflected in presented multi-proxy data from Imbramowice core. Observed changes in water conditions are probably a result of evolution of this lake, e.g.…”

“…The Imbramowice palaeolake is an important Eemian site pollen and diatom analyzed (Kaczmarska, 1976;Mamakowa, 1976Mamakowa, , 1988Mamakowa, , 1989Zagwijn, 1996;Cheddadi et al, 1998). The Eemian deposits have been the subject of many studies attempting to reconstruct the climate conditions of the last interglaciation (marine oxygen isotope stage (MIS) 5e) based on palaeobotanical and coleopteran data in Europe (e.g., Litt et al, 1996;Zagwijn, 1996;Aalbersberg and Litt, 1998;Cheddadi et al, 1998;Granoszewski, 2003;Klotz et al, 2003;Kupryjanowicz, 2008) and in Siberia (Granoszewski et al, 2005;Fagel and Mackay, 2008).…”

Application of Fourier Transform Infrared Spectroscopy (FTIR) for assessing biogenic silica sample purity in geochemical analyses and palaeoenvironmental research

“…Typ- ically, samples with residual values above 7% are marked by increased offsets between FTIR and XRF. In an attempt to reduce Residual c and so improve the accuracy of the FTIR contamination estimates, a three end-member training set was constructed consisting of BFC mod or PS1772-8 and standards of mica and montmorillonite (BFC mod -Mica/Mont and PS1772-8-Mica/Mont) to reflect the composition of the clay mineralogy in the Lake Baikal sediment record (Fagel and Mackay, 2008) (Fig. 6).…”

“…Indeed in some cases for heavily contaminated samples there is a noticeable deterioration in the residuals and accuracy of FTIR relative to XRF. With the clay mineralogy of Lake Baikal relatively constant over time (Fagel and Mackay, 2008), this implies that other less common aluminosilicates may be forming a large degree of the sample contaminants in addition to other inorganic and organic material. Accordingly, to maximise the accuracy of the future model fitting and so FTIR estimates of contamination, it is necessary to consider in detail how contamination matrices can vary between samples and identify all possible end-members.…”

Palaeomagnetic data from the late Cenozoic Tagay section (Olkhon Island, Baikal region, Eastern Siberia)

“…An indirect estimate of the time of formation of the strata can be made based on the sedimentation rates of lacustrine sediments because the tectonic regime in this region during the early Neogene was relatively stable (Mats et al 2010). According to various estimates, the sedimentation rate in Lake Baikal during the late Cenozoic varied from 2.6-3.5 to 10.1-15.1 cm / Kyr (Fagel and Mackay 2008;Kravchinsky 2017), which makes it possible to estimate the formation time of the clay stratum in the Tagay-1 section from 90 to 500 Kyr. However, according to Peizhen et al (2001), due to sharp climatic changes in the late Cenozoic (2 -4 Ma ago), rates of lake sedimentation increased dramatically, while in the Miocene they were generally significantly lower.…”