| Due to lack of data and complicated geological conditions,the Lower Fourth Member of Shahejie Formation and Kongdian Formation in the Yihezhuang-Bonan Area of Jiyang Depression has not received sufficient attention for exploration for a long time.This area is the “three new fields” for oil and gas exploration in Shengli Oilfield,and it is also one of the most realistic layers of reserve growth during the “13th Five-Year Plan” period.However,this area lacks systematic geological research,the structural characteristics and evolution process are still unclear,the source system and sedimentary system are unclear,and the control of tectonic activities on sedimentary systems is weak.These problems severely constrain further oil and gas exploration.The object of this paper is the Lower Fourth Member of Shahejie Formation and Kongdian Formation in Yihezhuang-Bonan Area.We comprehensively use seismic,drilling,logging and related analytical test data,and use the relevant theories and methods of structural geology,sedimentology and reservoir geology to systematically carry out sequence stratigraphic division of the study area.We also summarize and reproduce the tectonic style and tectonic evolution process of different sequence sedimentary periods,restore the prototype basin,determine the source system and sedimentary system types,and establish the development model of sedimentary systems in different periods.On this basis,we further clarify the control mechanism of tectonic activities on sedimentary systems.We hope to solve the above-mentioned basic problems that hinder the progress of exploration,so as to drive oil and gas exploration in the “three new fields” of Jiyang Depression.Red bed deposition was existed in the Lower Fourth Member of Shahejie Formation and Kongdian Formation in Yihezhuang-Bonan Area.We use seismic data to track the seismic reflection interface and identify the macroscopic stratigraphic interface,examine the stratigraphic interface through the climate change interface reflected by paleontological data,and use the acoustic time difference method and log data wavelet analysis to identify small-scale stratigraphic interfaces within the macroscopic strata.From macro to micro,from large scale to small scale,stratigraphic boundaries of Ek2,Ek1 and Es3 x in YihezhuangBonan Area are identified step by step,and Es4 x is divided into three sand groups from bottom to top.The present distribution range of residual strata in the Ek2 – Es4 x is gradually expanding,and the strata are NW-trending.The thickness of the residual stratum in the whole is distributed in the descending disk of the NE-trending fault.However,due to the influence of the Mesozoic and Cenozoic tectonic movements,the center of the residual stratum thickness in the sedimentary period of the Lower Fourth Member of the Shahejie Formation showed a certain trend of northeastward distribution.NW,NE and nearly EW faults were the dominated fractures in Kongdian Formation and the Lower Fourth Member of Shahejie Formation,which were composed of different structural patterns on the plane(such as parallel,oblique crossing and grid)and on the profiles("Y" shape,warping fault block,sliding fault step and graben and horst fault block).Obvious regularity can be researched in the development and evolution of main faults.The NW fault was the earliest fault in study,which was experienced of compressional thrust movement in late Triassic and negative reversion in early Cretaceous.The activity of Guxi fault and Chengnan fault was strong duiring red bed sedimentary period.All NE faults were gradually dying in Paleogene except Chengnan fault.The NE fault began to active in later period.The basin underwent three stages of tectonic evolution: conversion from NE compression stress field to NE extensional stress field before red bed sedimentation,from NE to NW extensional stress field during red bed sedimentation,from the dying of NW extension to the stage of depression after red bed sedimentation.the prototype basin of the red bed was subjected to intense denudation which was mainly controlled by the warping action of fault block and the differential uplift of the fault steps during the period of Kongdian Formation and the lower Fourth Member of Shahejie Formation.The basin showed the characteristics of fault and thickness in north,overlap and thinness in south.By restoring the palaeogeomorphology and paleoprovenance,it could be concluded that the basin controlling fault was turned from NW in Kongdian Formation to NW and NE combination controlled in the lower Fourth Member of Shahejie Formation.With the gradually increasing activity of NE fault,the sedimentary center migrated from NW thrown side to NE thrown side in later period.The overall sedimentary pattern of the study area are controlled by the development and evolution of the main faults in Kongdian Formation and the lower Fourth Member of Shahejie Formation.The sediments in study area were mainly derived from the uplifts around the basin in sedimentary period of red bed,including Chenjiazhuang uplift,Gudao uplift,Chengdong uplift,Yihezhuang uplift in order of supply capacity.Ancient gullies were existed in uplifts which have characteristics of big and small gullies corresponding to big and small fans,respectively.Sporopollen analysis also showed an arid paleoclimatic environment in red bed sedimentary period.The sedimentary background of the red bed sedimentary period in the study area was recovered by integrating the characteristics of paleogeomorphology,paleoprovenance and paleoclimate.Five sedimentary facies types,including alluvial fan,braided river,delta,fan delta and lake,are developed in the study area,and the characteristics of red bed under typical water exposure environment are developed.Tectonic activity plays a decisive role in controlling sedimentation,that take place in the following aspects: first of all,the difference of fault that in different activity period activity changed the paleogeomorphology;secondly,six types of deposition transport channels were formed under the effect of fracture and paleogeomorphology;thirdly,tectonic activity control the distribution of redbed sedimentary boundary and sedimentary formation,and lead to the difference erosion of redbed lastly. |
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