Palynological Assemblages And Paleoclimate Change From The Quantou-Qingshankou Formations In Chaoyanggou Area, Songliao Basin

Detailed core sample collections and descriptions have been made from the upper Quantou to lower Qingshankou formations in Chao-73 and Chao-75 wells of Chaoyanggou aera in Songliao basin. The length of sampled core is about 100 meters. Careful identification and analysis of Spore-pollen fossils, TOC andδ13Corg as well in the paper have been carried out.Well Chao-73 and Well Chao-75 is adjacent with the comparative beds of the collecting sample and the same lithology. The greyish-green mudstone in the Member 4 of Quantou Formation richs in pyrite. The grey and grayish-black mudstone in the Member 1 of Qingshankou Formation is of Ostracods,Esthenaus fossils and grainy pyrite .Palynomorphs are completely preserved and various in all of samples. Based on the palynological analysis of the 49 generas from Well Chao-73 and Chao-75 ,2 palynological assemblages are established : Schizaeoisporites-Tricolpopollenites-Qua- ntonpollenites assemblage is from the upper beds of the Member 4 of Quantou Formation;Cicatricosisporites-Cyathidites-Pinuspollenites is from the lower part of the Member 1 of Qingshankou Formation. Important spore and angiospermae pollen fossils such as Asterisporites,Cranwellia,Xinjiangpollis,Beaupreaidites and Quantonenpollenites have been obtained from the the upper part of the Member 4 of Quantou formation. They are Late Cretaceous in age. The reasonable geologic time of the upper Quantou formation may be later than Cenomanian deduced by the age of the upwards spore and angiospermae pollen fossils and the palynological assemblages. Therefore, the Lower/Upper Cretaceous boundary in Songliao Basin is, therefore, in the Quantou formation or underneath it, rather than between the Quantou and Qingshankou formations.Based on the ecological characteristics, climate and humidity condition for the vegetation of the sporopollen from the both of the wells, the palaeovegetation types have been reconstructed. The result shows that the paleoclimate changes from tropical semiarid-subhumid climate to subhumid mid subtropical climate to subhumid south subtropical climate. The analysis of TOC andδ13Corg benefits from Well Chao-73, indicating that they response well enough to the Cretaceous paleoenvironment and paleoclimate. During the sedimentary period of Quantou formation to Qingshankou formation in Songliao basin, the water tends to rise and becomes anoxic, and the deoxidized water leads to the organic matter massively preserved. The paleoclimate changes from torridity and aridity to warmth and humidity, with the temperature evidently descengded, then ascended in a litter range. The result is basically consistent with paleoclimate by the palynological analysis.