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Morphology of submerged terraces in southern Lake Baikal

© Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Numerous geological and geomorphological data suggest of both higher and lower levels of Lake Baikal in the past (Mats et al., 2002). The lake level lowering is usually documented by submerged wavecut/abrasion platforms, sedimentary unconformity and delta systems. Erosional surfaces in the shallow part of Selenga delta record the lake level fluctuations over the past 100 thousand years (Urabe et al., 2004). A series of unconformities in the upperpart of the sedimentary cover in the Malye Ol’khonskieVorota Strait distinguished at a depth of 40–45 m also indicates a regression of the lake during the Last Glaciation (Khlystov et al., 2008). Submerged terraces (wave-cut platforms) were found in the upper slope in the Valukan Cape area (Northern Baikal) at a depth of 40 m (Osipov and Khlystov, 2010). That is, a decrease in the lake level 40–45 m below the modern one in Late Pleistocene is confirmed by geological and geomorphological records, however, the spatial and time correlation of this level is still controversial. In this paper we present new data on the morphology and age of submerged terraces on the upper slope along the southeastern coast of Lake Baikal. In July 2016 the bathymetric surveying was carried out aboard the RV I.D. Papanin along the upper slope in three key regions located near Pankovka, Vydrinaya and Pereemnaya river mouths. Totally, 31 bathymetric profiles were run normal to the shelf break within the depth interval of 0–200 m to identify submerged terraces. A morphological analysis of upper slope was performed using both bathymetric and hypsometric (digital elevation model, DEM) data. Analysis of bathymetric data revealed 12 submerged terraces (T1–T12) at depths of 34–43 m (T1), 51–56 m (T2), 65–72 m (T3), 81–86 m (T4), 92– 96 m (T5), 106–112 m (T6), 119–122 m (T7) , 128– 129 m (T8), 137–140 m (T9), 160 m (T10), 166–179 m (T11) and 188 m (T12). Morphological analysis of bathymetric profiles showed that the shelf break is traced at depths of 15–17 m (an average of 16 m). The average slopes of the modern wave-cut platform (shelf) range from 1.6° (Pereemnaya) to 2.2° (Vydrinaya), an average of 1.8°. The average width of the platform varies from 350 m (Vydrinaya) to 760 m (Pankovka), which indicates a relatively prolongated lake level stabilization close to the modern conditions during both Holocene and Late Pleistocene, for example, during the Last Glacial Maximum (Osipov and Khlystov, 2010). The width of the submerged terraces ranges from 20 to 260 m (an average of 92 m), and the slope from 0.9 to 11.2° (an average of 4.4°). The widest terraces (>150 m) were observed at Pankovka and Vydrinaya areas (at depths > 80 m). At depths of 34–75 m (Vydrinnaya) and 41–177 m (Pereemnaya), submarine ridges were discovered, which were interpreted as terraced moraine complexes correlated with the glacial maxima of MIS 4 and MIS 6.