Structural Characteristics And Evolution Of Mesozoic In Dongying Depression

Dongying Depression,as the secondary tectonic unit in Jiyang Depression,is one of the regions with the highest abundance of oil and gas resources and the highest degree of exploration.There are imbalances in the layers of oil and gas,the majority of the oil and gas distribute in the middle layer of the Shahejie Formation,The exploration level of deep strata is relatively low.and the unclear understanding of the structural evolutionary characteristics is the main reason for restricting deep exploration.The Mesozoic is the important transition stage of the Dongying Depression and the whole Bohai Bay basin.The structural development,evolution and mechanism are complicated.In this paper,through the study of the Mesozoic structural characteristics of Dongying Depression,the evolution process is defined and we will provide reference for deep oil and gas exploration and restore the basin of the various stages of the prototype.At the same time,it will further enrich the understanding and study of the Mesozoic tectonic evolution in eastern China.The Mesozoic structural strata in the Dongying Depression are divided into two tectonic sublayers of the Lower-Middle Jurassic and Lower Cretaceous,and the residual distribution characteristics of the Mesozoic strata are affected by the Shicun-Pingnan-Binxi fault,which residual formation is divided into two major regions: the thickness of the Mesozoic strata is gradually thickened in the western region;In the eastern area,the residual strata of the hanging wall of Chennan fault is the thickest areas,the residual thickness characteristics of the overall areas perform the northwest distribution.The fault system of the pre-Tertiary in the Dongying Depression is mainly divided into NW,NE and near EW trending faults.The NW-trending faults are superimposed reformation by the NE-and near-EW-trending faults,and the pre-Tertiary faults are relatively simpler,compared with the shallow faults,and the structural pattern is simple,showing the extending tectonic style and negative inversion tectonic style.The Mesozoic main active faults in the Dongying Depression are the northwest distribution.As its extension of the fault in the Jiyang Depression show: They converge in the southeastern end and spread in the NW(W)end.They main develop the negative inversion tectonic pattern,few thrust fault and some folds,Dongying sag is not a separate depression.It was divided into two main tectonic units by Shichen-Pingnan-Binxi fault,belonging to the part of Jiyang northwest graben..In the Mesozoic,the Mesozoic-Early Triassic region was subjected the stable stratigraphic sediments,which belonged to large-scale inland sediments.The Late Triassic belonged to the extrution denudation period,and the NW-trending thrust faults were formed to form terrain height difference,which leads to the difference of denudation.The Jurassic belonged to the transition period of the pressure-Zhang,and the structural action was weak,which was controled by the Late Triassic NW-trending thrust and fold.The strata were filled and draped,and distributed in the north-west.In the early Cretaceous,Dongying Depression belonged to the stage of tension and tectonization,which was controlled by the negative reversal fault,forming the northwest semi-graben.Forming a settlement center in the fault hanging wall,and the formation is overlying from the fault to the distance,with the lower-middle Jurassic stratum forming two reverse wedges in the section.