四川盆地北部苍溪组含铀层系沉积特征及沉积期古气候特征研究OA

Based on the principles of sedimentary systems and facies,this paper conducts a comprehensive analysis of the sedimentary characteristics and paleoclimate of Cretaceous red beds in northern Sichuan Basin with the methods of field outcrop observation,drilling data analysis,and sporopollen fossil analysis.The results show that Lower Cretaceous Cangxi Formation vertically developed a"dual structure"with coarse grains in the lower part and fine grains in the upper part.Horizontally,four main types of sedimentary facies were developed:alluvial fan facies,braided river facies,meandering river facies,and littoral-shallow lacustrine facies.The sedimentary environment favorable for sandstone-type uranium mineralization is primarily sandy braided river deposits.The known uranium mineralization and uranium ore bodies are mostly hosted in paleo-scour troughs,mainly distributed in Cangxi-Wangcang-Nanjiang-Tongjiang area.Based on the types and assemblage characteristics of sporopollen fossils from Cangxi Formation,the sporopollen assemblage is characterized by the abundant presence of Classopollis and a small amount of Dicheiropollis,which basically constrains the age of Cangxi Formation to Valanginian to Hauterivian stages.Combined with the plant community dominated by Cheirolepidiaceae and the presence of charcoal-rich organic matter in the light-colored rhythmic layers of Cangxi Formation,this study indicates that the climate environment in northern Sichuan Basin during Early Cretaceous was characterized by an alternation of arid and humid climate.Specifically,the lower part of each rhythmic layer of Cangxi Formation represents warm and humid(or subaqueous)light-colored deposits,while the upper part represents red beds(floodplain deposits)formed under an arid climate.