The Stratigraphic Comparison And Sedimentary Characteristic Of Akeshake Group Of The Lower Carboniferous In Bole Basin

The Bole Basin Carboniferous stratum develop abundant shale,which has the basic geological conditions of shale gas reservoir.Based on the data of outcrop profile and paleontology,combining with previous research results,and guided by the theory of classical sequence stratigraphic framework,this paper study on sequence division and stratigraphic comparison for the 44 outcrop profiles in Bole Basin.It shows that the Akeshake group can be divided into two three-stage sequences,which SQ₁ is the lower subgroup of the Akeshake group and SQ₂ is the upper subgroup of the Akeshake group,thus establishing the Bole basin Lower Carboniferous Akeshake group sequence stratigraphic framework.In total,the stratum thickness show the trend of thinning from southwest to northeast and northwest to southeast.The Akeashake group is characterized by clastic rocks and carbonate rocks mixed sedimentation.It can be determined develop the delta,carbonate platform,volcanic debris flow and littoral-neritic sea sedimentary system by analyzed the sedimentary facies and abundant outcrop and paleontology data.Bole basin is located in the southern margin of Baerkashi-west Junggar late Paleozoic residual ocean basin at the Akeshake group deposition period.The sediment sources are mainly originated from the northern Tacheng ancient land and the southwest Yining ancient land.The ocean area of Bole basin was enlarged after a short period of volcanic activity,and almost completely covered by seawater in the early of early Carboniferous period?SQ₁?.The deep shelf sediments are developed in the area of Bole City-Jinghe County,and the volcanic debris flow deposits are developed in the east of Bocan 1 well.The delta front was developed in the Wenquan County-L3 well and Sailimu Lake-L3 well area by the control of the Tacheng and Yining ancient land source.the seawater gradually receded to the southwest in the end of early carboniferous?SQ₂?,the sedimentary range of deep shelf is decrease.On the contrary,The sedimentary area of delta front is enlarged.As a whole,the Akeshake group experienced two stage of regression.This paper considers that Bole basin favorable sedimentary environment of shale is deep shelf facies by the comprehensive study on the paleogeographic background,sedimentary characteristics and sedimentary facies distribution.The thick black mudstone is developed in the area of Bocan 1 well-Bole City by the control of the two-way source,which provides a favorable theoretical basis for the next shale gas exploration and development.