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The northeastern Tibetan Plateau is located at the convergence of the Asian winter and summer monsoons and westerlies; thus, this area has witnessed historic climate changes. The Xunhua basin is an intermontane basin on the northeastern margin of the Tibetan Plateau. The basin contains more than 2000 m of Cenozoic fluvial–lacustrine sediments, recording a long history of climate and environmental changes. We collected the mid‐Miocene sediments from the Xunhua basin and used palynological methods to discuss the relationship between aridification in the interior of Asia, global cooling, and uplift of the Tibetan Plateau. Based on the palynological analysis of the Xigou section, Xunhua basin, the palynological diagram is subdivided into three pollen zones and past vegetation and climate are reconstructed. Zone I, Ephedripites–Nitraridites–Chenopodipollis–Quercoidites (14.0–12.5 Ma), represents mixed shrub–steppe vegetation with a dry and cold climate. In zone II, Pinaceae–Betulaepollenites–Ephedripites–Chenopodipollis–Graminidites (12.5–8.0 Ma), the vegetation and climate conditions improved, even though the vegetation was still dominated by shrub–steppe taxa. Zone III, Ephedripites–Nitrariadites–Chenopodipollis (8.0–5.0 Ma), represents desert steppe vegetation with drier and colder climate. The palynological records suggest that shrub–steppe dominated the whole Xigou section and the content gradually increased, implying a protracted aridification process, although there was an obvious climate improvement during 12.5–8.0 Ma. The aridification in the Xunhua basin and surrounding mountains during 14.0–12.5 Ma was probably related to global cooling induced by the rapid expansion of the East Antarctic ice‐sheets and the relatively higher evaporation rate. During the 12.5–8.0 Ma period, although topographic changes (uplift of Jishi Shan) decreased precipitation and strengthened aridification in the Xunhua basin on leeward slopes, the improved vegetation and climate conditions were probably controlled by the decrease in evaporation rates as a result of continuous cooling. From 8.0 to 5.0 Ma, the rapid development of the desert steppe can be attributed to global cooling and uplift of the Tibetan Plateau.

To better understand the vegetation and possible paleoclimate change, we recovered a palynological record obtained from the ZKD14 core covering from the Sifangtai and Mingshui Formations in the northern Songliao Basin, northeastern China. Based on the abundance and variations in determined palynomorphs, two palynological assemblages can be distinguished, including Schizaeoisporites-bisaccate-Tricolporopollenites and Taxodiaceaepollenites-bisaccate-Tricolporopollenites. These palynological assemblages are assigned to the late Campanian-Maastrichtian stage based on the geological range of some important elements and the correlation with relevant assemblages of other areas. In this paper, we applied a sporopollen-climate transforming methodology, which uses the percentage of xerophytic and thermophilic taxa to indicate stratigraphic trends of humidity and temperature, respectively. Then two vegetation and paleoclimate phases were reconstructed based on the ecological habits of the parent plant, as well as the abundance variation in xerophytic and thermophilic taxa: (i) The vegetation type was interpreted to reflect a mixed conifer forest with varying pteridophytes landscape, presenting a hot and arid subtropic climate during the Sifangtai to lower part of member 2 of the Mingshui Formations. (ii) The vegetation type was characterized by a conifer-dominant landscape. Accordingly, the climate turned more humid and colder during the upper part of member 2 of the Mingshui Formation. The global cooling event (Campanian-Maastrichtian Boundary Event: CMBE) which occurred between 72.0-70.0 Ma appears to have an important influence on the climatic condition of Songliao Basin.

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