The High-Frequency Sequence And Deposition Characteristics Of The Glutenite Of Shahejie Formation In The Zhuangxi Area Of Zhanhua Depression

Glutenite is an important sedimentary type and a favorable facies zone for oil and gas reservoir in lacustrine rift basin,which has an important scientific and industrial significance.The glutenite is usually developed close to the boundary fault,which is a near-source fan-shaped sedimentary body.Owing to the internal sequence interface is not obvious in the glutenite,it is difficult to carry out stratigraphic correlation and establish an isochronous stratigraphic framework,resulting in restricting the further analysis of the distribution of sedimentary facies and the main controlling factors.In recent years,the developments of cycle stratigraphy have provided a new idea for high frequency cycle division and stratigraphic correlation.In this study,taking the Changdi steep slope zone,Zhuangxi area,Zhanhua Depression as an example,we use the theory of sedimentology,sequence stratigraphy,cyclic stratigraphy and seismic sedimentology to integrate the detailed stratigraphic correlation,high-frequency sequence stratigraphy division,distribution and evolution of sedimentary systems of glutenite during the fourth and third member of the Shahejie formation(Es4-Es3),based on the data of core,well logging and seismic interpretation.On the basis of the above,the main controlling factors of the development of glutenite in the study area are discussed.The following research results are obtained:(1)Under the constraint of stratigraphic sequence framework,the cycle stratigraphy analysis was carried out in the deepwater mudstone area,and extended to the basin margin.It was proposed that the high-frequency sequence division scheme of nine sand groups in the upper sub-member of Es4 and the six sand groups in the lower sub-member of Es3 were determined,and the upper sub-member of Es4 and the lower sub-member of Es3 were a complete third-order stratigraphic sequence,respectively.(2)A variety of fan sedimentary types were identified,and their coupling relationship with tectonic evolution were determined.In the study area,fan-delta,nearshore subaqueous fan and sublacustrine fan were developed.In the period from the upper sub-member of Es4 to the lowstand systems tract of the lower sub-member of Es3,the Changdi fault was in the extension stage,and the sedimentary facies are mainly fan-delta,followed by offshore subaqueous fan and sublacustrine fan.During the period of the upper sub-member of Es3,the changdi fault was in the strike-slip stage,and the sedimentary facies were mainly fan-delta.(3)The paleogeomorphology and distribution of provenance system in different periods were reconstructed.The provenance of the upper sub-member of Es4 was mainly the low uplift of the eastern Changdi fault zone,followed by the northeast area.Ne-trending echelon provenances were developed in the southeast of the upper sub-member of Es3,while SE and NE-trending grooving provenances were developed in the lower sub-member of Es3.(4)The distribution and evolution of glutenite at different periods were obtained by establishing the sedimentary facies markers of core facies,logging facies and seismic facies.From the upper sub-member of Es4 to the lowstand systems tract of the lower sub-member of Es3,the sedimentary systems in the eastern and northeastern parts were mainly fan-deltas.However,counterparts in the northeastern parts were mainly nearshore subaqueous fans.In the period from the highstand systems tract of the lower sub-member of Es3 to the upper sub-member of Es3,the east of changdi low bulge and oblique echelon provenances are mainly fan delta.Based on the above research results,this paper deepens sedimentary characteristic,distribution and evolution law of glutenite during the Es4 to the Es3 in the Changdi steep slope zone of Zhuangxi area,and provides an important scientific theoretical basis for the exploration and development of this area in the later period.