The Study Of Sequence Stratigraphy In The Northern Continental Slope Of AIAU

As an interdisciplinary discipline of sedimentology and stratigraphy,sequence stratigraphy has been widely used in various stages of oil and gas exploration and development.The study of sea level change,sequence stratigraphic framework and sedimentary system can be used for the portrayal of sand body shape and boundary in favorable reservoir facies belt and the prediction of the spatial development position of oil and gas reservoirs.The predecessors mainly conducted basic geological research on the stratigraphy,tectonics,sedimentary cycles and sedimentary filling sequences,and established a relatively rough sequence stratigraphic framework,which has not been established since the Middle Miocene in the EU-EA basin.In addition,the relationship between the development of sedimentary sequence and tectonism and global sea-level fluctuation is not yet clear.According to the above problems,based on the extent of exploration in the study area,this paper uses the 2D seismic data to determine the sequence interface on the basis of the predecessor's sequence division scheme by recognizing the termination relationship of reflections on the sequence boundaries and the unconformity surface.Dividing the depositional sequence of third-order cycle by transgressive-regressive sequence model and clarifying the internal sequence stratigraphic structure by using seismic line drawing techniques.The sedimentary environment and phase distribution pattern of the continental shelf,land slope and deep sea basin are determined according to the changes of the top and bottom surface morphology and thickness of the stratigraphy.The characteristics of sequence stratigraphic framework since the Middle Miocene in typical seismic profiles can be summarized by using transgressive-regressive sequence model to divide the genetic unit and dentifying of transgressive system tracts with regressive system tract.On this basis,the sedimentary sequence divided by this paper and the five regional unconformities identified by previous generations from the Middle Miocene are compared with global sea-level change curves to analyze the relationship between the development of sedimentary sequences and global sea-level changes.Through the above work,the following conclusions have been made:(1)Through reflection termination analysis,14 third-order sequence interfaces have been identified since the Miocene in the study area.From bottom to top,they are: SB1,SB2,SB3,SB4,SB5,SB6,SB7,SB8,SB9,SB10,SB11,SB12,SB13,SB14;which are divided into 14 third-order sequences,from the bottom to the top,they are: SQ1,SQ2,SQ3,SQ4,SQ5,SQ6,SQ7,SQ8,SQ9,SQ10,SQ11,SQ12,SQ13,SQ14.(2)The sedimentary strata in the continental shelf area of the study area are mostly aggradation stacking,and the characteristics of the seismic reflection are mainly medium frequency and medium-strong amplitude more than continuous reflection,and the characteristic of the delta phase short axis discontinuous reflection.The depositional strata of the continental shelf and the upper continental slope are mainly composed of the retrogradation stacking during the transgressive period,descending type foreset stacking and progradation stacking during the regressive period and the seismic reflection characteristics are mainly the middle-low frequency weak-medium amplitude discontinuous reflection.There are mostly vertical aggradation stacking,showing blank reflection,disorderly reflection or low frequency weak amplitude continuous reflection in deep water area.(3)In the SQ1 to SQ13 sequence,the transgressive system tract and the regressive system tract are developed.The delta facies sedimentary strata are developed in the region of the south-west and southeast of the SQ1 to SQ6 sequence,and the SQ2 and SQ5 regressive system tract in the southwest of the south-west developed the retrogradation of slope fan and a pelvic floor fan,and the region of slope in the southeast SQ6 to SQ14 developed argillaceous wedge,which is converging to the basin direction.Transgressive system tract developed depositional strata for the retrogradation stacking in the shelf edge and inner slope,the seismic characteristics are mainly low frequency middle amplitude relatively continuous reflection.The regressive system tract is mainly marked by the accumulation stacking,the foreset with aggradation,the descending type foreset of the shelf edge,the deep water fan progradation,and the characteristics of seismic reflection are mainly low frequency weak-medium amplitude and continuous reflection.The shelf break with overall northward migration since the Middle Miocene.(4)The sedimentary sequence divided by this paper are compared with global sea-level change curves and the curve of third-order sea-level change of other regions.It is concluded that the development of sedimentary sequence in this area is closely related to the change of the global sea-level,and the previous views on the tectonic control of the development of the sedimentary sequence in this area are inaccurate.