Structural Characteristics Of Dongying Movement And Restoration Of Denudation Amount In Nanpu Sag

Dongying movement in Nanpu depression,occurring in the late Oligocene,is a regional tectonic movement with wide range of activities and high intensity of activity,which is in the period of the basin transition from the rifting stage to the depression stage.Due to the relatively few studies done by predecessors,there are great controversies about the occurrence time,tectonic properties and formation mechanism.Based on the detailed interpretation of the seismic data of Nanpu Sag and the logging data,the structural deformation characteristics of Dongying movement are analyzed,its occurrence time is determined,its structural properties are discussed,the erosion thickness in each area is calculated,the ancient thickness of the Dongying formation is restored,and the paleotectonic evolution is analyzed.On the basis of this,the mechanism of its dynamics is discussed.The Dongying movement is mainly represented by tectonic uplift,angle unconformity,formation depletion,fault activity and magmatic activity in Nanpu Sag.The sediments of the tectonic uplift area were denuded,resulting in the deletion of some strata in the Dongying formation and the Sha Hejie formation and the apparent angular unconformity on the seismic profiles.The Dongying movement also formed a large number of tensional and tensional faults in NE,NE and near EW directions.In the plane,the NE trending fault is dextral and the NW fault is left lateral.It is assumed that the stress direction is stretching extensional deformation property near the north south direction.In the profile,most of the faults are cut shallowly and cut through Dongying formation,a few parts cut down the base.There are more magmatic activities associated with the Dongying movement in the study area.The magma activity is intense,and the volcanic rocks in the Ed₁-Ng are widely distributed,mainly distributed in Nanpu,Beibu,Lao Yemiao and Gao Shangpu areas.The erosion caused by Dongying movement is mainly distributed in the Nanpu No.5 structure,Lao Yemiao and Gao Shangpu areas.The denudation occurs mainly in the vicinity of the fault.The erosion amount is the largest in the Gaoliu area and the erosion thickness is between 0-600m.There is little erosion in the 5 areas of the Lao temple and Nanpu structure,and the erosion thickness is between 0-320m.Denudation in other areas is not obvious.The Dongying movement occurred in the sedimentary period of the first number of the Dongying formation of the late Oligocene,strengthened in the end of Oligocene and stopped in the early Miocene?about 19.5M?.It was a fault block movement formed in the deep mantle material up welling in an extensional environment from NW-SE to SN.The Dongying movement maybe related to the joint action of the subduction and rolling back of the Pacific plate and the eastward extrusion due to the long-range effect of collisions of the India Eurasian plates.