Late Oligocene leaf and pollen flora of Southwestern Siberia: taxonomy, biogeography and palaeoenvironments

Late Oligocene leaf assemblages from four sites in Southwestern Siberia (Kurgan, Tyumen, Omsk oblasts) are described. Twenty-three leaf taxa and 3 reproductive structures represent local vegetation of a lake (Salvinia, Typha, Phragmites, Nelumbo, Hemitrapa, Liquidambar, Pterocarya, Alnus, Populus, Salix, Nyssa). Additionally, 57 spore and pollen taxa were recorded from one site (Shish River). Gymnosperms dominate the assemblage with ~30% Pinaceae and ~25% taxodiaceous (papillate) Cupressaceae pollen. Ferns and peat mosses (Sphagnaceae) comprised ~6%. Angiosperms were dominated by Fagaceae, Betulaceae, Juglandaceae and Ulmus and comprised a few exotic elements (Liquidambar, Eucommia, Nyssa, Symplocos); scarce herbaceous plants reflect lakeshore vegetation. The flora of the Turgay type comprised old elements (Nelumbo protospeciosa, Liquidambar europaea, taxodiaceous/papillate Cupressaceae, Quercus sect. Protobalanus) and taxa present in Siberia/Kazakhstan during the Paleogene with later arrivals in Europe (Ulmus pyramidalis, Quercus pseudocastanea, Alnus julianiformis, Byttneriophyllum tiliifolium). A few taxa were endemic in the late Oligocene of western Siberia (Trapa praeconocarpa, Platycrater iljinskajae sp. nov.). Combined macrofossil and palynological evidence places the Shish River site flora into the late Oligocene Zhuravka (Turtas) Formation. Floras of similar composition from western Eurasia are commonly middle Miocene or younger in age highlighting the dynamic spatiotemporal evolution of temperate Eurasian floras during the Cenozoic.