A Study of the Cretaceous-Tertiary Sequence Stratigraphy of Tarim Basin, Xinjiang

According to the comprehensive analyses of the depositional sequence of the Cretaceous Tertiary outcrop sections in Tarim basin, combined with the seismic sequence and drilling information, the authors hold that the Cretaceous Tertiary strata can be divi ded into 30 depositional sequences in the southwestern depression and 24 depositional sequences in the northwestern depression. This suggests that, due to their different tectonic settings and sedimentary environments, the 3rd order sequences in these two depressions cannot be correlated directly one by one. Ordered stacking of several 3rd order sequences forms 2nd order supersequence and the system tracts of the supersequences. The ordered stacking has three types, namely progradation association, retrogradation association and aggradation association. Each supersequence is formed by different types of 3rd order sequence group. On the basis of the study of 2nd order sequences, the Cretaceous Tertiary strata may be subdivided into 4 supersequences, which can be correlated synchronously in Tarim basin, and the cycles of relative sea level reflected by them are basically the same. The Cretaceous Tertiary strata in south Tibet were also influenced by seawater of the Tethys. The depositional sequences and sea level changes in Tarim basin are consistent with those in south Tibet. This proves that these two areas are both influenced by Tethyan tectonic movement and eustatic change. The rapid uplifting of the Qinghai Tibet plateau and the relative subsidence of the Tarim basin since Miocene have resulted in the difference between these two areas in sequence types and rates of sea level change.