Palynological assemblages of Holocene typical black soil profile from northern Songnen Plain and its restricts to environmental evolution

Paleoclimate and paleoenvironmental evolution is one of the most critical issues in the study of the formation and evolution of black soil.Reconstruction of paleo-vegetation, paleo-climate and paleo-environment, and prediction of the evolution of the climate and environment in the black soil area have become hot spots in black soil research.Fifteen sporopollen samples were collected from a typical black soil profile in the Keshan County of the northern Songnen Plain for pollen research, and total organic carbon in some soil samples from the same stratum was AMS¹⁴C dating.Systematic analysis, identification, and research have shown that three sporo-pollen assemblages from bottom to top were developed in the black soil profile of Keshan County.The lower pollen assemblage is represented by Planted Poaceae-Echinate Asteraceae-Tamarix-Polypodiaceae, the middle pollen assemblage is represented by Tamarix-Chenopodium-Polypodiaceae-Echinate Asteraceae, and the upper pollen assemblage is represented by Pinus-Chenopodium.Comprehensive Quaternary geology and geomorphology, pollen, AMS¹⁴C, and element geochemistry analysis all suggest that the typical black soil was mainly formed in the Great Warm Period since the 7500 a B.P.of the Middle Holocene.Which formed in the warm and semi-humid climate of the Songnen Plain, the vegetation is mainly grassland vegetation with herbaceous shrubs.Neotectonic movement is the main internal driving force that controls the evolution of the natural environment in the typical black soil area.The Late Pleistocene yellow clay is the parent material of the typical black soil in the Keshan black soil area, and the development process of the black soil is the process of of soil blackening.