Open unforested landscapes were predominated in the late Pleistocene (MIS 3 and MIS 2) of West Siberian Plain. This is shown in particular by the entomological data. Insect late Pleistocene assemblages from the north (70-60° N) were considered as the arctic type, and from the south (57-51° N) were assigned as non-analogous periglacial type or so called “Otiorhynchus-type fauna” (Legalov et al., 2016; Gurina et al., 2019). Forests are not typical for this time, and insects associated with arboreal vegetation were found in the late Pleistocene deposits sporadically.
One of the sites where Quaternary deposit insect assemblages include forest insects are Suzun-1 (53°43'54'' N, 82°10'54'' E) and Suzun-2 (53°44'00'' N, 82°11'01'' E). Both are located in the Suzun River valley, right tributary of upper Ob River (Novosibirskaya Oblast, Russia). Obtained radiocarbon dates are as follows. 24893–25966 cal yr BP for Suzun-1 correspond to the end of MIS 3, and 20379–20699 cal yr BP for Suzun-2 correspond to the beginning of MIS 2.
Insect assemblages Suzun-1 and Suzun-2 represented mostly by Coleoptera are very similar to each other. They include a lot steppe species (Harpalus salinus, H. amputatus, Porcinolus murinus, Otiorhynchus cf. ursus, O. subocularis) and several tundra species (Diacheila polita, Curtonotus cf. alpinus, Pterostichus (Cryobius) spp.) that is typically for the periglacial assemblages. However, in contrast to other known late Pleistocene entomocomplexes of the West Siberian Plain, some forest species (Phloetribus spinulosus, Carabus henningi, C. regalis, Pterostichus cf. altainus, Pterostichus cf. maurusiacus) were found in the Suzun-1 and Suzun-2 sites.
The presence of bark beetle Phloetribus spinulosus associated with Picea allows reconstructing fir forest at river valleys. However the proportion of steppe and forest species of Coleoptera in the Suzun assemblages shows the forests probably occupied restricted area only, and opened steppe landscapes predominated in the region. The high similarity of Suzun-1 and Suzun-2 insect assemblages confirms a gradual MIS3 – MIS2 transition in the region, and indicates the forest refugium existed here quite long time, at least a few thousand years.
The study was partially supported by the Russian Foundation for Basic Research (project no.19-04-00963‐a) and the Federal Fundamental Scientific Research Program for 2013–2020 (project no. AAAA‐A16‐116121410121‐7).
