Sedimentary Characteristics And Tectonic Evolution Of The Early Carboniferous Akeshake Formation In The Atengtao Mountain Area Of Yining Block

In this paper,the Early Carboniferous Akeshake Formation in the Atengtao Mountain area of the Yining Block is taken as the research object,profile?rock assemblage?basic sequence?size analysis?biological characteristics?U-Pb geochronology of detrital zircon?stratigraphic correlation and depositional environment are analyzed in the section.The main achievements are as follows:The rock assemblages of the Early Carboniferous Akeshake Formation in Atengtao Mountain area can be divided into two major assemblages: terrigenous clastic rocks and shallow Marine carbonate rocksAngular unconformity contact exists between the Early Carboniferous Akeshake Formation and the lower early Carboniferous Dahalajunshan Formation in the Atengtao Mountain area.The contact surface is a phase transition surface,and the two are depositional unconformity,Which belong to sequence unconformable contact.Angular discordant contact was observed between the Akeshake Formation and the overlying late Carboniferous Yishijilike FormationPalynology samples were collected from the clastic rock section of the Akeshake Formation in this study.Palynology assemblages were relatively monotonous and poorly preserved.However,in terms of such poor composition,Auroraspora and Lycospora were the main assemblages,suggesting that the Early Carboniferous epoch was more likely.Coralline in shore-neritic facies and brachiopods were collected from carbonate rocks of the Akeshake Formation with abundant fossils,Such as Gigantoproductus sp.,Kueichouphyllum sp.,Neolithostrotion sinense.Age determined as Early Carboniferous.Detrital zircon U-Pb chronology shows that the youngest detrital zircon age was 325±5 Ma,suggests that at the time of this set of gravel deposits,upstream have age was 325±5 Ma source of material supplies for the strata of rock mass,the age of zircon magma crystallization age,so the rock combination comprehensive the above information age should be later than 325 Ma,To sum up,The age of Akeshake Formation in the Atengtao Mountain area is in Early Carboniferous.The clastic rocks of the Akeshake Formation in the Atengtao Mountain area are derived from :(1)volcanic rocks and intrusions of the Dahalajunshan Formation in the periphery of Atengtao mountain;(2)Early late Carboniferous volcanic debris in the early paleozoic Nalati Island arc belt in the south.The source model indicates that when the clastic rocks of The Akeshake Formation were deposited in the Atengtao Mountain area,the uplift of the Dahalajunshan Formation was denuded,which contributed a large amount of pyroclasts.In the southern Nalati tectonic belt,volcano-magmatic rocks are exposed and the topography is high in the south and low in the north.At the same time,detrital zircons record that volcanic activity remained in the Yining Block in the late Early Carboniferous period,and some volcanic materials were added to the sedimentary areaBased on the study of the basic sequence,particle size analysis,biological characteristics and stratigraphic correlation of the akshak formation,the sedimentary facies of this set of stratigraphic clastic rocks are identified as fan delta plain subfacies,fan delta front subfacies and coastal shallow subfacies.The sedimentary facies of carbonate rocks include the foot facies of carbonate platform,the front slope facies of carbonate platform and the organic reef facies of the platform edge.The tectonic evolution of Atengtaishan area from late Devonian to Early Carboniferous is discussed in this paper...