Distribution And Its Environmental Impact Of Lacustrine Deposit In Western Margin Of Ordos

The western margin Ordos locate in two important tectonic belts of China with complicatedtectonic activities.It is in the arid and semi-arid region with fragile ecological environment.Lacustrine facies strata in this region can faithfully record the information of tectonic activitiesand the environment evolution.We find the lacustrine facies strata distribution of the west margin of Ordos Basin by fieldsurvey and indoor experiment analysis.We find the lacustrine facies strata distribution of the westmargin of Ordos Basin by field survey.Dating method was used to study the age of lacustrinefacies strata formation.Left-lateral strike-slip fracture arc beams are formed in southern westmargin of Ordos Basin by the uplift effect of Tibet plateau. While there are east-west fractures innorthern Basin. The difference in the lacustrine facies strata distribution is obvious as well.Thenorth was a large enclosed lagoon.The lake facies formation have the same sedimentary structureand with small deformation.The gray diatomite clay layer is characteristic.It seems like the climateis the main factor.In southern west margin of Ordos Basin,the lacustrine facies strata is found inthe Yellow River valley, Qingshui river valley, GuShuiHe valley.The sedimentary structure oflacustrine facies strata is diverse,and the distribution is rathe dispersed.Most of the lacustrinefacies strata are small lakes.It is supposed that the tectonic activity is the main factor.Mengjiawan section， Ningxia,China，in the middle of the west margin of Ordos Basin.Thearea is the entrance of the Yellow River into the WeiNing basin.The study area is in the arid andsemi-arid area of the northern hemisphere.The ecological environment is single and fragile.Studyon Mengjiawan section has both tectonic and climate significance.The first stage:(30.75~21.64kaB.P.) frequent fluctuations of cold and dry climate,and the wind was stronger; The second stage:(21.64~18.99ka B.P.) dry and cold climate with strong wind;The third stage:(18.99~17.55kaB.P.) cool with weak wind activity; The fourth stage:(17.55~9.6ka B.P.) the climate is dry andcold with strong wind.The fifth stage (9.6~6.4ka B.P.) warm and humid climate with weak wind;The sixth stage:(6.4ka B.P.) warmer and more humid climate with weak wind.