Stratigraphic Characteristics And Sedimentary Environment Of The Lower Cretaceous Shengjinkou Formation Of The Changji Area,Xinjiang

This paper mainly studies the stratigraphic characteristics and sedimentary environment evolution of the Shengjinkou Formation in Changji area,Xinjiang.Through field measurements of typical profiles and indoor thin-slice observations,combined with particle size analysis and carbon and oxygen isotope analysis,five main terrigenous clastic rocks were identified,and the lacustrine facies of the Lower Cretaceous Shengjinkou Formation were divided into lakeside subfacies,and subdivided into beach-bar microfacies,sand-mud mixed beach microfacies and mudflat microfacies.Gain the following new knowledge:The Cretaceous Shengjinkou Formation(K₁sh)was mainly composed of a set of terrigenous clastic sediments.There are three different sedimentary sequences in the Shengjinkou Formation:The bottom of the formation is feldspar-clastic sandstone,which has the characteristics of fine upper and lower coarse;The middle section of the formation is dominated by siltstone and silty claystone;The lithology of the upper part of the mouth formation is micro-fine sandstone and feldspar shale sandstone,which has a thick sedimentary sequence.The grain size parameters show that with the basin subsidence during the Cretaceous period,the shallow lake deposits formed by the strata.The bottom,middle,and top of this group show the difference in sedimentary hydrodynamics of the Shengjinkou Formation,reflecting the evolution characteristics of alternating flow velocity at that time.Carbon and oxygen isotopes indicate that the carbon and oxygen isotope composition of the sandstone calcite cements in this group has the characteristics of marine carbonate composition.The analysis of paleo-salinity and paleo-temperature shows that the sedimentation of the Shengjinkou Formation is affected by the burial depth,and it has a mixed fluid environment during its formation.Provenance analysis shows that the source area of the sediment comes from the northern Tianshan.Comprehensive regional geological data concluded that:the influence of Yanshan movement,uplift in the Early Cretaceous of North Tianshan up,Junggar Basin internal slow overall settlement,the study area is located in the southern margin of victory Chrysostom group of shallow lacustrine sedimentary basin environment.During the uplift of the North Tianshan Mountains,the detrital materials that were denuded continuously entered the lake basin and settled along with the changes in hydrodynamics.The shore lake subfacies of the Shengjinkou Formation are further refined from bottom to top into beach bars,sand-mud mixed beaches and mud flats.The study further analysis is important in the Junggar Basin evolution.