This paper presents the results of a palynological study of the natural outcrops of the Lower and Middle Jurassic on the Kelimyar River (Outcrops 5, 6, 7, 14, and 16) and two boreholes, Middle-Nakynskaya and Ygyata-Tyungskaya 1, in Eastern Siberia. The Ukugut, Tyung, Motorchuna, Suntar, Kyrin, and Kelimyar formations were studied. Six biostrata with dinocysts were established for the Upper Sinemurian–Toarcian. The analysis of the stratigraphic ranges of dinocysts in the sections allowed the identification of the stratigraphic ranges for important genera of dinocysts, which enabled the updating of the geochronology of some biostrata. Three main stages of the evolution of dinocysts in the Early Jurassic in the Siberian Paleobasin were characterized by the appearance, diversification, and disappearance of some orders of dinocysts at certain times. Seven biostrata (beds with characteristic palynoassemblages) were established for the upper Sinemurian–Toarcian on the basis of the study of the taxonomic composition of spores and pollen of land plants and successive changes in the composition of the palynospectra.