Sedimentary Environment And Evolution Of The Early Carboniferous In The Weining Area

The research of sedimentary environment has an important guiding significance on the formation,preservation,development and utilization of fossil fuels,such as coal,oil and natural gas.In this paper,with the theories of sedimentology,petroleum geology,mineral petrology,reservoir geology and organic geochemistry as guiding theories and the characteristics of deposition,microscopic pore structure and trace fossils as research objects,the developmental characteristics,sedimentary environment and sedimentary facies of the upper strata of the Datang Formation in the area are studied and discussed with the comprehensive application of wild outcrops field survey means,microscopic identification,biological trace fossil identification methods.According to the condition of the outcrop of Carboniferous strata in Weining area,four sections are carried out field reconnaissance and measurement,respectively DaTang formation section in the Luduizi area of Weining,DaTang formation of Jiusi member in Liudongqiao area of Weining,DaTang formation section of Shuicheng black woods,and Bai Yanqing section in area of Weining.The field observed results show that the lithology of the Datang Formation is dominated by sandstone,shale,mudstone seams,limestone and marl,with the characteristics of fast lithologic changing and narrow transition range.Through the systematic study of trace fossils,9 species of trace fossils in 3 genus are identified and described,respectively ? fodinichnia:Chondrites fenxiangensis,Chondrites filifalx,Chondrites expansus,Chondrites antiquus;?pascichnia:Phycodes palmatus,Phycodes cicinatusr,Palaeophycus wutingensis;? repichnia:Dimorphichnus,Taphrhelminthopsis auricularis.Based on the combination characteristics of the fossil fossils and the sedimentary environment,three relics were established,respectively Chondrites relic combinations,Chondrites-Palaeophycus relics combination,and Phycodes relic combinations.Combined with the characteristics such as lithology and trace fossil,the change of sedimentary environment in the study area is discussed through scanning electron microscopy(SEM)analysis,ordinary thin section observation and X-ray diffraction whole rock analysis.It is concluded that the Carboniferous Datang Formation in the study area has experienced multiple transgression-regression processes,which is dominated by transgression.The early sedimentary environment of the Carboniferous Datang Formation gradually changed from the coastal sandy marshes to the local typhoon silt facies,and muddy shale is deposited and developed.The later Datang Formation experienced the process of transgression-regression processes,and sedimentary environment changed from the local platform to the open platform,and the fine mud is deposited and developed.Based on the analysis of the evolution of paleogeographic facies,it is considered that the controlling factors of the evolution of sedimentary facies are mainly influenced by tectonic fracture activity and provenance erosion intensity.