Paleoclimatic information in stratigraphic records and its relation to the formation of hydrocarbon source rocks-A case study of the Paleogene strata in the Huanghekou subbasin of the Bohai Bay basin, China

Recent study has revealed that the formation of good hydrocarbon source rocks in a subbasin depended on favorable paleoclimatic conditions and paleolake basin environment and was controlled by the tectonic setting of rapid subsidence during the downfaulting stage.This paper focuses on the controls of paleoclimatic conditions over the formation of hydrocarbon source rocks.According to the data of sporopollen and algae in samples from representative wells in the Huanghekou(Yellow River mouth) subbasin,Bohai Bay basin,and lithofacies characteristics of the area,the authors have reconstructed the paleoclimatic and paleoenvironmental conditions of the area in various epochs of the Paleogene.The results reveal that during the Paleogene in the Huanghekou subbasin there were four warm-humid stages when the paleolake basin water body developed.Furthermore,the four warm-humid paleoclimatic stages well correspond to four high-quality hydrocarbon source rock beds,which indicates that the warm-humid paleoclimatic conditions may have exerted important controlling effects on the formation of hydrocarbon source rocks.Lastly,the mechanism for the paleoclimate affecting the formation and preservation of source rocks is discussed.