Tectonic Subsidence History and Tectonic Evolution of Langfang-gu'an Depression in Bohaiwan Basin, Eastern China

Based on the date from numbers of boreholes and seismic lines,the estimation of tectonic subsidence shows that Langgu depression experienced two episodes of rapid subsiding,two episodes of weak subsiding and two regional rapid... [ view full abstract ]

Based on the date from numbers of boreholes and seismic lines,the estimation of tectonic subsidence shows that Langgu depression experienced two episodes of rapid subsiding,two episodes of weak subsiding and two regional rapid uplifting periods since Palaeogene.The first rapid subsidence time was in Ek-Es4,which was caused directly by the forming of Daxing fault at the late of Yanshan movement.The second and also the largest subsidence time was in Es3,different lifting regularity which was caused by the continuous up warping of Daxing fault is the main reason of this subsidence.With an obvious east-west difference,late Es3 was the major uplift and erosion period.And the eroded intensity of East is much greater than the west region under the influence of Langgu movement.Combined with regional background,the evolution of Langgu depression was divided to two stages:the Rift subsidence stage(Ek-Es3),and the Thermal subsidence stage(Es2-Em).Actually the former can ben divided to the Initial subsidence(Ek-Es4) and the Tilted fault phase(ES3).The later can be divided to Block up differences of differentiation stage(Es2-Ed) and Regional depression of filling stage(Nm).The early rapid subsidence is consistent with the extension period of the basin for about 23 ma,and mutation for late slow subsidence.The depocenter was controlled by Daxing fault.And it was in the Southwest of the depression during Ek-Es4.when Tongbozhen fault strongly acts after Es3,it moves to Tongbozhen groove.