Late Cretaceous Palynology(Spores, Pollen, Algae), Climate, And Lacustrine Conditions In Songliao Basin

Cretaceous climate was warmer than today. The Songliao Basin contains one of themost important Late Cretaceous non-marine deposits in China for the research of thepaleoenvironment and paleoclimate. This research is based on core samples from theSK1（S） borehole. The strata sampled are the upper part of the Quantou Formation tomember2of the Nenjiang Formation, where spores, pollen, dinoflagellates, and othermicrofossils are abundantly preserved.Based on analysis of the spores and pollen fossils from the core samples, thefollowing six fossil assemblage zones have been recognized in ascending order: theCicatricosisporites-Cyathidites-Pinuspollenites,Schizaeoisporites-Cyathidites-Classopollis, Cyathidites-Schizaeoisporites,Schizaeoisporites-Cyathidites-Proteacidites, Proteacidites-Cyathidites-Dictyotriletes,and the Lythraites-Callistipollenites-Schizaeoisporites zones. The six fossil zonesrange from the late Cenomanian to early Campanian.The Late Cretaceous dinoflagellate cysts in the Songliao Basin are of highabundance and low diversity. Specific phytoplankton types reflect salinity changes ofthe Songliao Lake. Paleoecology of the dinoflagellates suggests that sediments ofmembers2and3of the Yaojia Formation (K₂y²⁺³) were deposited in a freshwaterenvironment, whereas members2and3of the Qingshankou Formation (K₂q²⁺³) andmembers1and2of the Nenjiang Formation (K₂n¹⁺²) were deposited in freshwater tobrackish water environments.Combined with the paleoecology of dinoflagellates and the palynomorph biozones,valuable information of the paleoclimate was provided. The quantitative analyses ofspores and pollen fossils, such as vegetation type, climate type, and humidity type,diversity and dominance, indicate a relatively sub-humid, mid-subtropicalpaleoclimate, with slight climatic fluctuation and/or temporal change.