| Yuncheng Basin is a Cenozoic graben basin,located in the southwest of Shanxi Graben System,with Emei fault block platform in the north,Zhongtiaoshan in the east and south,and the overall trend of the basin is NE.The active faults in the Yuncheng Basin are relatively developed,and the direction of the faults is mainly NNE,NE,and NEE.These faults form the structural framework of the basin and control the structural deformation and seismic activity of the basin.The neotectonic activity determines the structural geomorphic pattern of Yuncheng Basin and affects the geomorphic evolution.Based on the coupling relationship between basin filling and structure.This paper is based on the project of "mapping of 1:50000shangguo(I49E005012)and yuncheng county(I49E006012)covered areas in Yuncheng Basin",which was carried out by the Institute of Geomechanics,Chinese Academy of Geosciences,mainly studies the sedimentary sequence and sedimentary facies characteristics of Yuncheng Basin by using the method of sedimentary basin analysis.Through the field investigation of active faults,the scratches on the fault plane are counted,and the stages and characteristics of the structural stress field in the area are preliminarily established by combining the kinematic and dynamic characteristics.Finally,the Yuncheng Basin is analyzed The relationship between sedimentation and structure.The following research results and understandings have been achieved:1.The sedimentary characteristics of the Cenozoic in Yuncheng Basin show that:Since Neogene to early Pleistocene,Yuncheng Basin has been characterized by a set of fluvial lacustrine deposits,dominated by lacustrine deposits.During the early Pleistocene,the fault controlled extensional fault basin continued to sink and the lake basin continued to expand,thus developing a wide range of Sanmen ancient lake;From the end of early Pleistocene to the Middle Pleistocene,influenced by the transformation of tectonic stress field,the Sanmen ancient lake in Yuncheng Basin began to shrink gradually.Due to the tectonic activity,Emei platform was relatively uplifted,and the river facies deposition was reduced in the lower Yuncheng Basin.The loess was deposited on the platform with higher ground potential,namely Lishi formation and Kehe formation.Since the late Pleistocene In addition to the residual lakes in Yuncheng Basin,the other sedimentary systems are dominated by theDingcun formation of fluvial facies,and the Shiyu formation in the basin with lower terrain is mainly deposited,and the loess accumulation on the platform with higher terrain is widely developed;In Holocene,it mainly deposited in alluvial proluvial lake and swamp facies.2.The study on the fault structure of basin controlling boundary in Yuncheng Basin shows that: During the Cenozoic,the marginal fault system experienced three stages of tectonic stress field transformation: NE-SW compression and NW-SE extension stress field in Neogene;NW-SE compression and NE-SW extension at the late of early-Pleistocene;near E-W compression and N-S extension at the end of late Pleistocene-Holocene.3.The analysis of sedimentary structural history shows that:(1)At the end of the early Pleistocene,the tectonic stress field changed from NE-SW compression and NW-SE extension stress field environment to NW-SE compression and NE-SW extension stress field environment,and formed the corresponding fault system,reformed the original NNE basin pattern,and Sanmen ancient lake within Yuncheng Basin began to die out gradually.The sedimentary strata changed from early fluvial and lacustrine facies to fluvial facies.(2)In the early stage of late Pleistocene,the tectonic stress field was characterized by near E-W compression and N-S extension.Under the influence of tectonic activities,the relative uplift of Emei platform was completely cut off,forming a relatively closed system,which also transformed the previous fluvial facies dominated sedimentary system into shallow lake facies and loess accumulation. |
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