Evolutionary analysis of Mesozoic and Cenozoic basins in northeastern Zhanhua sag

To find out the evolutionary characteristics of Mesozoic and Cenozoic basins in northeastern Zhanhua sag,the balancing cross sections of three NW-trending and three NE-trending connecting-well seismic sections were reconstructed, according to the principle that stratum length is conservative.And the variation of extensional proportion in geological periods of each section was analyzed. The basin evolution stages from Mesozoic to Cenozoic in the northeastern Zhanhua sag can be divided into some stages,including the period of early to middle Triassic,a large inland depression developed;in late Triassic the study area was uplifted wholly and denuded,and NW-trending thrusting faults began to develop;during early to middle Jurassic there was a 'filling-up' process on the undulate topography formed in advance;in the period of Jurassic to Cretaceous former NW-trending faults inversed negatively and transferred to extend,the stage of rift basin began,meanwhile in some areas,stretching and thrusting structures grew;the rift basin continued developing during Paleogene,the NW-trending faults went successive action,and many NE(E)-trending faults also began acting during this stage;in Neogene the study area began to regional subsidence as a depression.