Sedimentary Geological Characteristics And Basin Dynamics Significance Of Kaijianqiao Formation In Northern Kangdian

The Kaijianqiao Formation is an important stratigraphic unit of the Nanhua System in Kangdian area,and mainly with a set of coarse-grained terrigenous clastic rocks and intermediate-acid volcanic rocks.It is one of the most important sedimentary rocks of the Neoproterozoic rift system in South China with great theoretical significance and academic value to reveal the Neoproterozoic continental rift pattern,development process,and even related global paleocontinental events.This paper selects Kaijianqiao Formation in Ganluo and Dechang,northern Kangdian area,to carry out a comprehensive research on stratigraphic,sedimentological and basin tectonic analysis,aiming at optimizing the regional correlation framework of the Kaijianqiao Formation,determining sedimentary facies type and deposits filling patterns to clarify the structure of the prototype basins and their regional correlation.The paper has made the following major new understandings:1.The study of sedimentary sequence and sedimentary facies in the Kaijianqiao Formation reveals that braided river deposit is the main sedimentary facies type in this area,and the braided river in this area is dominated by far-source fan.2.The rosette diagrams of the large-scale oblique bedding pre-accumulation at 5 sites in Ganluo and Dechang areas show that the paleocurrent of the Kaijianqiao Formation is from west to east,the direction of sediment diffusion is to east,and the provenance is to the west of the study area.3.The statistics of sandstone skeleton grains of the Kaijianqiao Formation show that the provenance area is volcanic rocks area,and the western part of the study area is volcanic rocks development area of the basin at that time.4.The prototype basin of the Kaijianqiao Formation is a rift basin,which can be divided into Suxiong Sag and Dechang Sag in the northe rn part of Kangdian area,based on the sedimentary facies,diffusive direction of sediments,stratigraphic contact relationship and geochemical characteristics of contemporary volcanic rocks.Based on the above new understandings and combined with previous research results,the structure,development stage of Kangdian rift system and its relationship with Nanhua system rift are analyzed and discussed.