Study On The Sedimentary Characteristics Of Sand-Conglomerate Bodies In The Es4s Members Of Northern Bonan Depression

Bonan Depression located in the middle of Zhanhua Sag,During the deposition of Es4,controlled by the tectonic evolution and the palaeogeomorphology features, There havedeveloped a large number of glutenite bodies in the north of Bonan Sag. By analysis of datasand materials in the work area compositely,summarized the sedimentary faciesflags,determined the glutenite bodies’ sedimentary facies types of northern Bonan Depression.Based on the full use of datas and materials in the work area, and under the guidance ofpredecessors based on sink simulation experiment established the nearshore subaqueous fansand-conglomerate body depositional genetic model, and combined with sequencestratigraphy、sedimentology other methods, to glutenite bodies’ deposition stages in the northof Bonan Depression conduct with fine division and correlation,established the high precisionsequence stratigraphic framework in the work area. Combined with the glutenite bodiesgenetic types that have been determined、sequence evolution characteristics and regionalgeological settings, established the glutenite bodies’ deposition glutenite mode in the workarea,and clear the glutenite bodies’ deposition distribution and evolution law in the work areafinally.The glutenite bodies’ genetic types in the north of Bonan Depression were the nearshoresubaqueous fan sand-conglomerate body. The rock type in the work area mainly were thelithic feldspathic sandstone, followed by the feldspathic lithic sandstone,the rock have a highlevel of heterogroups,granule mixed with big and small, low compositional and structuralmaturity; Sediment grain size probability cumulative curve shape mainly were wide andgentle on the arch、low oblique two-stage and arches form, reflect the gravity flowsedimentary characteristics; Massive bedding、graded bedding and parallel bedding were themost typical bedding structure in the work area,and the main level structure was the scoursurfaces, reflect the glutenite bodies rapid accumulation and event deposition features; Thelogging curve have the basic form of box-shaped、 bell-shaped、 finger-shaped andlinear-shaped,the box-shaped and bell-shaped logging curve was the most common;Grain-supported coarse conglomerate phase facies was the typical facies type in the work area.In the north of Bonan Depression there were recognized the Ⅲ-class sequenceboundaries T6、T7and Tg（the regional boundaries）; in the control of T6and T7there wererecognized two big sequence boundaries Q1、Q2let the work area divided into divided intothree Ⅳ-class sequences in detailed, they were Es4s-1、Es4s-2and Es4s-3.On the basis of theregional sequence stratigraphic framework that have been established, to make a fine divisionand correlation to glutenite bodies’ deposition stages in the north of Bonan Depression. Theresults of divided deposition stages were: fan No.yi282was divided into seven depositionstages; fan No.yi110was divided into twelve deposition stages; fan No.yi159was divided intofifteen deposition stages.Through contrast between the well, found that each period glutenite bodies overlaid oneach other、inherited development、continued backing in the vertical，to the direction of thefan root some period have cut cavitation usually. The fan bodies of deposition thickness fromthe fan root to front become thinning, sediment grain size become thinner,the fan takes theshape of the wedge Insert into lacustrine mudstones. Fan takes the shape of lenticular laterally,the Intermediate layers were large thickness to sides become thinning.The fan bodies aroundmigration swing, make compensation deposition with each other.From sand group3to sandgroup1,the glutenite bodies’ period were reduced, thickness were thinning from the bottom tothe up, the glutenite bodies retrograding to the source direction gradually. The glutenitebodies’ distribution close to the ancient landscape, the ancient climate and other factors,during the deposition of Es4, in the north of Bonan Depression were high mountains and deepvalleys, ditch and girder appeared alternately, along with three old gully developed three bigfan from the west to the east. The glutenite bodies were the result of multiple perioddeposition superimposed, three big fan developed contiguous, thirty-four internal small fanbodies were around the boundary fault (the Chengnan fault zone) distributed like skirt-shaped.With the replacement of the old and new geological era, extensional fault continued activitiedin the northern steep slope, the boundary faults scale-out step by step regularly in differentperiods,led to the glutenite bodies’deposition boundary performaned go backing.