中国科学院南京地质古生物研究所机构知识库

The Jiuxi Basin is the earliest developed petroleum production area in China, and the Lower Cretaceous strata in this area are the main source rocks in this basin. Although the strata in this area are rich in fossils and have been researched for a long period, different interpretations of their geological age have been proposed. In this study, palynological samples collected from the Chijinbao Formation (Hanxia Section) and the Xiagou Formation (Hongliuxia Section) in the Jiuxi Basin were analyzed, and abundant fossil palynomorphs were identified. Based on detailed identification and statistical and comparative analyses, five palynological assemblages can be defined from the bottom to top of these strata. Among these, three assemblages are established in the Chijinbao Formation in the Hanxia Section. Their geological ages are Berriasian-Valanginian in the Early Cretaceous. Two assemblages are established in the Xiagou Formation in the Hongliuxia Section. Their geological ages are Hauterivian-Barremian in the Early Cretaceous. By analyzing the distribution characteristics and ecological environments of the different palynoflora types, we speculate that in the Berriasian-Valanginian, the vegetation of the basin mainly consisted of coniferous forests. During this time, ferns were scarce, and the climate was generally warm and humid. By the Hauterivian-Barremian, the vegetationmainly consisted of coniferous forests, ferns and cycads, and the climate was generally humid. The short-duration increase in Cheirolepidaceae reflects a short and slightly arid period in the early stage of the Hauterivian-Barremian. Furthermore, small-scale arid-humid climate fluctuations occurred during the deposition of both formations. (C) 2020 Published by Elsevier B.V.