Late Cenozoic palynofloras revealing significant environment and climate changes in Changbai Mountain area, NE China

Abstract

The present climate in the Changbai Mountain area, NE China is warm with abundant rainfall. It is mainly affected by the wet air mass from the Sea of Japan. Local vegetation belongs to the warm temperate mixed conifer and broad-leaved forest, with a mountain cold temperate coniferous forest belt occurring at an altitude of over 1100 m. The Neogene vegetation history of this region is not yet well understood because of the lack of palaeobotanical data. Here we report a systematic palynological result of a plant-bearing diatomite sequence at Badaogou of Changbai Mountains in Jilin Province, which shows distinct vegetation and environment changes during the late Neogene. Seven palynological assemblages are recognized in the diatomite deposits from a freshly closed mine (Zones M-I and M-II), and an outcrop (Zones I–V) respectively in ascending order. Pollen data indicate a dominant woody angiosperm plants such as Ulmus, Quercus, Pterocarya and Fagus etc. at first (Zone M-I). Subsequently, gymnosperm plants mainly represented by Pinus, Tsuga, Picea and Abies show an increase (Zone M-II), and become predominant at a lowest sample in the outcrop (Zone I), distinguished by rich Picea, along with large amount of Tsuga, Pinus and Abies. Pinus increases significantly, while Picea remains higher value, and Abies and Tsuga become limited in the following assemblage (Zone II). Woody angiosperm pollen Tilia, and terrestrial herbs and shrubs including Asteraceae and Chenopodiaceae show their first sign of increase in Zone III, and become more distinguishable in Zone IV. Picea rises again in Zone V. Pollen assemblages display a successive change of vegetation between the mine (Zones M-I and M-II) and the outcrop (Zones I–V), reflecting their continuity in time. Based on the Ar–Ar dating, the outcropping deposits (Zones I–V) are the Latest Pliocene in age, approaching to the Plio-Pleistocene boundary. Consequently, pollen data in this study indicate a major turnover from the warm temperate mixed conifer and broad-leaved forest (Zones M-I and M-II) to the cold temperate coniferous forest (Zone I) during the Late Pliocene in the Changbai Mountain area. It also displays some subsequent fluctuations including the warm temperate mixed conifer and broad-leaved forest partly recovered in Zones III and IV, and decreased again in Zone V. It shows for the first time how local vegetation responses to the global climate deterioration in the Late Pliocene of NE China. The overall changing process is more or less comparable with some simultaneous vegetation changes in North China and Central Japan. The terrestrial herbs and shrubs in the assemblages are not significant comparing with other areas in North China, reflecting the influence of wet air mass from the Sea of Japan. Meanwhile, Tsuga is gradually disappearing in the upper assemblages as a result of continuous lower temperature.