Large Columnar Stromatolites For The Cambrian Furongian Series In Western Shandong Province

Western Shandong Area is rich in Cambrian outcropping and sedimentation in the eastern margin of the North China Platform.Large columnar stromatolites are developed for the Cambrian Furongian Series in the Feicheng Dengjiazhuang Section,Zaozhuang Xianrendong Section and Tengzhou Sangcun Section,which shows the spectacular sedimentological phenomenon in Cambrian.Based on field observation,according to sedimentary characteristics and lithofacies sequence,the Furongian Series in Western Shandong Area is divided into 3 three-order sequences: Changshan Formation constitutes the first three-order sequence.The Fengshan Formation are divided into 2 three-order sequence.Stromatolites are developed in the sequence forced regressive system tract of third-order sequence composed for Changshan Formation in Dengjiazhuang Section,Fengshan Formation for Xianrendong Section and Sangcun Section,its larger diameters represent the specific sedimentary types of the phanerozoic.The characteristics of stromatolites are described in terms of megastructure,macrostructure,mesostructure and microstructure.Specifically,the stromatolites in the study area are all produced in the form of biostrome,the columns are arranged closely perpendicular to the ground,belong to SH-V type according to the classification of stromatolites.The longitudinal section shows a rough and gentle lamination,the laminations are mostly in the form of dome,and the gentle slope laminae can be seen locally.The observation of microscopic characteri stics shows that stromatolites for the Furongian Series in the Western Shandong Area are composed of dark micrite and microsparry,microclots,dolomites and biodetritus can be seen inside,there are also abundant and obvious calcified microorganisms.The presence of diverse calcified microbial fossils represents the complex calcification of cyanobacteria dominated by stromatolites.Furthermore,Special irregular networks can also be seen in dense micrite.The discovery of sponge spicule and filamentous calcified microbial is more likely to result from the joint action of epigenetic sponges with microorganisms.Stromatolites are formed by the trapping and binding of clastic materials and mineral precipitation by microorganisms,and the microbial mat formed by microbial community affects the formation of carbonate by controlling the balance between precipitation and dissolution.Stromatolites in Cambrian,Proterozoic and modern marine are quite different.Macrostructure may indicate different water depth and hydrodynamic conditions,while the microstructure of stromatolites is mainly controlled by the microbial community.The formation of stromatolites is closely related to the complex interaction between microbial mats and their surrounding environment,and the microbial ecosystem influences the formation of microbial carbonate by controlling the balance between precipitation and dissolution.Large columnar stromatolites for Furongian series in Western Shandong Area provides a typical example for the study of Cambrian stromatolites in the North-China platform.This provides a typical rock record for the occurrence of phanerozoic cyanobacteria calcification and microbial carbonate recovery.However,the formation mechanism and calcification mechanism of stromatolites need to be further studied and considered.