Campanian-Maastrichtian palynomorph from the Sifangtai and Mingshui formations, Songliao Basin, Northeast China: Biostratigraphy and paleoflora

We recovered a Campanian-Maastrichtian palynological record in transitional succession from the Sifangtai to Mingshui formations of the Songke Core-1 (North) (SK1 (N)) in the Songliao Basin, Northeast China. These formations are composed mainly of various colored mudstones and sandstones. The lithofacies variation suggests that the paleoenvironment changed from flood plain to lake. Most of the palynomorph assemblages are dominated by gymnosperm pollen, followed by spore of pteridophyte, and angiosperm pollen. On the basis of the first occurrences of marker genera within the succession, we identified four palynomorph interval zones (in ascending order): the Jianghanpollis, Chenopodipollis, Toroisporis, and Betulaceoipollenites interval zones. The first two interval zones are found from flood plain and levee deposits. The third one is recognized from lake basin plain-lake basin slope deposits. The last one is found in delta deposits within lakeshore. We consider that environmental changes are the major factors that formed component of Campanian-Maastrichtian assemblage in the Songliao Basin. In addition, the Jianghanpollis and Chenopodipollis interval zones are assigned to the Campanian, whereas the Toroisporis and Betulaceoipollenites interval zones date as the Maastrichtian. Thus, the Chenopodipollis/Toroisporis zonal boundary approximates the C/M boundary. Triprojectate pollen such as Aquilapollenites is regarded as marker taxa in the study section and other areas within the Aquilapollenites Province during the Campanian-Maastrichtian. However, Wodehouseia spp. have yet been confirmed within the study section, although this genus has appeared in Campanian-Maastrichtian deposits in other areas. This is one of the important clues to understand regional difference of local flora in these ages.