Palynological record of the Cretaceous ZKD14 core (Songliao Basin, Northeast China) and its paleoclimatic significance

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.