Lacustrine Deposits Record And Tectonic Significance Of Tongzilin Region In Yalong Downstream

Panxi area is one of the important area of rich resources and energy, andit also has experienced frequent neotectonic movements with complex geological conditions, solving problems of abundant geological information, regional stability and environment hazard has vital scientific significance. Based on grainsize analysis, magnetic susceptibility and the pollen analysis, this dissertationconducted field research of the quaternary deposits, chronological sequence andsedimentary environment, reflects Yalong downstream Tongzilin lacustrine depo-sits and neotectonic movement characteristics since the upper late Pleistocene.Yalong downstream Tongzilin region is a set of loose lacustrine sediment, whichage is about2.5ka~1ka during the upper late Pleistocene-early Holocene. This set oflacustrine deposits experienced the changes from river facies to lacustrine facies andto fluvial facies. In the upper Late Pleistocene, erosion uplift deposits gravelaccumulation,then transformed into lacustrine sedimentary accumulation period; theHolocene, river erosion reappearing but not cut through the lower lacustrine sediment.According to the drilling data, Tongzilin formation distributes along Yalong river,Jinsha river and Anning river discontinuously, bead-shaped lakes may be due to thelarge landslide, debris flow, or the ancient earthquake debris blocked rivers or formedby relative decline of the earth’s crust.Baesd on the characteristics analyses of the magnetic susceptibility, grainsize and pollen analysis, restored the paleoenvironment and paleoclimate variation characteristics of Yalong downstream Tongzilin formation since the upperlate Pleistocene.Can be devided to7different periods:(1) hydrodynamic weaker,less rainfall, pinus mainly, needle-leaved forest-grassland, cold and slants dry;(2) rainfall reduced, weak hydrodynamic conditions, lower temperature, needle-leaved forest, grassland, cool and moderately dry;(3) hydrodynamic instability,needle-leaved forest, more rainfall,warm and humid;(4) temperature reduced,humidity decreased, weak hydrodynamic conditions, pinus mainly, needle-leavedforest, cold and dry;(5)weak and unstable hydrodynamic condition, drier;(6)Similar to the fifth stage, dry;(7) hydrodynamic conditions is stronger compared to phase6, cold and dry.Through the small interval sampling on the lake sediment, radiocarbon dating and grain size analysis, magnetic susceptibility and pollen analysis, recoverthe climate and environment evolution sequence in Full last gliacal period, and discusses the characteristics of the formation of tectonic movement of basin.