The Cyclic Sedimentation And Sea Level Change Characteristics Of The Taiyuan Formation In Western Henan Province

Based on the deposit characteristic researches of lithology,sedimentary structures,sedimentary sequences,body fossils and ichnofossils in the Lower Permian Taiyuan Formation from geological sections of Yuzhou,Dengfeng and Jiaozuo areas in Western Henan Province,this paper analyzed the sedimentary environments and sedimentary systems,and established the sedimentary facies assemblages and sedimentary cycle sequences,and then,formulated the general characteristics of cyclic sedimentation and sea level changes in the sedimentary period of the Taiyuan Formation in this study area,meanwhile,the sea level change curve of the early Permian was drawn.On the basis of the above work,the regional stratigraphic correlation markers were determined and the transgressive and regressive evolutionary law was discussed.The main progress was followed:(1)Through systematic summary and detailed analyses of sedimentary characteristics in the Taiyuan Formation within this study area,4 sedimentary facies(shallow marine,tidal flat,barrier island and lagoon facies)and 2 sedimentary systems(barrier-free coast and barrier coast sedimentary systems)were identified.(2)According to the sedimentary cycles characteristics of transgression and regression,the sedimentary sequences of the Taiyuan Formation was divided respectively into 3first-order sedimentary cycles and 9 second-order sedimentary cycles in Yuzhou area,and meanwhile it was divided into 3 first-order sedimentary cycles and 11 second-order sedimentary cycles in Jiaozuo and Dengfeng area.(3)On the basis of the response relationship between cyclic deposition and sea level rise and fall,the stratigraphic correlation framework of the Taiyuan Formation in Western Henan Province was established,and it is proposed that the sedimentary period of the Taiyuan Formation in this area experienced two major sea level rises and falls,and two large-scale transgression were identified within the Taiyuan Formation in Yuzhou and Dengfeng area respectively,however,there have been three large-scale transgressions in Jiaozuo area.(4)Based on the analyses of regional stratigraphic correlation and cyclic sedimentation,it is proposed that the evolution law of transgression and regression within the sedimentary period of the Taiyuan Formation in this area,namely,in the early sedimentary period of the Taiyuan Formation(Early Asselian),the seawater invaded this area from the northeast,the order of transgression is firstly Jiaozuo,and then Dengfeng,finally Yuzhou area;in the middle period of the Taiyuan Formation deposition(Late Asselian),the changes from tidal flat to lagoon facies developed during sea level rise,and then the order of sedimentary facies formation were tidal flat ? barrier island?tidal flat?lagoon?tidal flat facies during sea level fall,in the meantime,it has been identified that Jiaozuo area experienced two Minor transgression;Finally,in the late period of the Taiyuan Formation deposition(Sakmarian-Artinskian),Sea water intruded this area from southeast,the order of transgression was from Yuzhou,Dengfeng to Jiaozuo areas successively.