Study on Cretaceous sedimentary paleoenvironment and sedimentary characteristics of Kedong tectonic belt in southwestern depression of Tarim Basin
Despite the great exploration potential of the Cretaceous in Kedong tectonic belt of southwestern depression of Tarim Basin,controversy still exists about the understanding of its sedimentary evolution.In this paper,the sedimentary paleoenvironment and sedimentary evolution of the Cretaceous in Kedong tectonic belt were discussed based on the trace element test results of fine sediments of Kizilsu Group and Kukebai Formation in Kedong 101 Well,as well as the core,outcrop and logging data.The results show that the mean values of paleoclimate indices Sr/Cu,Rb/Sr and δEuN of Kizilsu Group and Kukebai Formation are 56.37,0.12 and 1.48,respectively,and the average values of redox indices U/Th,V/Cr,V/(V+Ni)and δCeN are 0.29,0.52,0.62 and 0.86,respectively.The average values of ω(Li)and Sr/Ba are 26.27 μg/g and 0.014,respectively.Trace elements suggest an arid,highly oxidized,and low-salinity terrestrial freshwater environment.During the sedimentation process of the Kizilsu Group and Kukbai Formation,the drought intensity and salinity from bottom to top show an increasing trend,and the oxidation intensity shows a decreasing trend.Sedimentary facies of Cretaceous in Kedong tectonic belt is characterized by the evolution of braided river delta-tidal flat,in which the Kizilsu Group and Kukbai Formation develop shallow water braided river delta deposits with a relatively fast sedimentation rate,and the Dongba Formation develops marine tidal flat deposits.Laterally,Cretaceous in Kedong tectonic belt shows a decreasing trend of sediment grain size from west to east.Compared with the eastern region,the braided river delta plain of the lower part of the Kizilsu Group is relatively well developed,the delta front sand body of the Kukebai Formation is thicker and the grain size is relatively coarser,while the intertidal zone of the Dongba Formation is more developed in the western region.
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