Sequence Lithofacies Paleogeography of Cambrian in Tarim Basin

Based on the materials of outcrops,wells data and seismic data,and guided with sequence stratigraphy theory,the sequence stratigraphy of Cambrian in Tarim basin is divided into three second-order sequences(SS1,SS2,SS3) which belong to the typeⅡsequence,developing TST and HST,and fourteen third-order sequences.Combined with the characteristics of sedimentary facies,six sequence-based lithofacies paleogeographic maps of Cambrian are compiled with the mapping units of sedimentary system tracts.The result shows a rapid and short-term sea level rise in TST and a long slow sea level decline in HST during deposition ages of both SS1 and SS2.The depositions in the middle and western regions of Tarim basin changed from restricted platform and open platform deposition in TST to evaporation platform and restricted platform lagoon in HST.The eastern region of Tarim basin accepted the shelf and basin filling.at this time,the whole basin area was relatively large.In the SS3 period,the platform and open platform deposition existed in the middle and western regions of Tarim basin,In comparison with the SS1 and SS2,the deposition areas became small,and the shelf deposit area expanded.The deposition environment in the eastern part of basin gradually turned to carbonate platform in the SS3 HST.