Keywords: 
• sedimentary evolution /
• rimmed carbonate platform /
• reef-bank facies /
• Lianglitage Formation /
• Upper Ordovician /
• Tazhong area

Abstract: Tazhong area is located in middle Central uplift in Tarim Basin. The at the north is Manjiaer depression, and the south is Tanggubazi depression. Its strike direction is NW-SE. Based on the datas of seismic, well logging and core, the authors establish the sequence stratigraphic framework and the evolution of the sedimentary facies of Lianglitage Formation in the Tazhong area.
The depositional rimmed platform include open platform facies and platform margin facies in Lianglitage Formation depositional stage in the Tazhong area. The open platform facies can be divided into patch reef, grain bank, tide flat, interbank sea, intra-platform bottomland. The platform margin facies can be divided into reef mound, carbonate mud mound, granule shoal, interbank sea. The Lianglitage formation's sedimentary sequence can be dividied into transgressive systems track and highstand systems track, and they contain ten parasequence sets. The transgressive systems track contains parasequence sets from 1 to 4, which are retrogradational stacking or aggradational stacking. Their lithology are mainly mudstone and grainstone with interbed biolithite. The highstand systems track includes parasequence sets from 5 to 10, which are aggradational stacking or progradational stacking. Their lithology are grainstone and biohermal limestone with interbed lime mudstone.
In the transgressive systems track, the sedimentary trap gradually cover the whole research area. In the parasequence sets 1 to 2, the Z20—Z11—Z4—T162—T78 wells and the Tazhong NO.1 fault are the boundaries of platform margin/open platform and platform margin/slope. The northwest of T86—Z18—T21 wells is blockmass. In this period, the open platform mainly deposit interbank sea, and the intra-platform bottomland distribute in the T10—T11 wells and T79—T43 wells. The width of platform margin is about 1～10 km, and its length is about 160 km. It also mainly deposit the interbank sea, and the granule shoal develop longitudinal zonality. In the parasequence sets 3 to 4, the blockmass boundary shrink to the western part of Z19—Z17—T45 wells. The Z18—Z20—Z4—T162—T262 wells and the Tazhong NO.1 fault are the boundaries of platform margin, open platform, slope. In this period, the water circulates unobstructedly, so that form the aggradational stacking and retrogradation stacking parasequence sets, which form the thick grainstone and micrite in both platform margin and open platform. The width of platform margin is about 2～10 km, and its length is still about 160 km. Because the deposition range of granule shoal and mud mound gradually expand, the rimmed sedimentary character become obvious.
In the highstand systems track, the accretion rate of accommodation is equal to (or smaller than) the rate of sedimentation, so that form the aggradational stacking and progradational stacking. In the parasequence sets 5 to 7, the range of platform margin expand, its width is about 3 km to 14 km, and its length is about 210 km. A lot of carbonate mud mound deposit, and the reef mound deposit in the range of T83 well to T78 well. The granule shoals have the largest sedimentary trap and thickness, longitudinally stacked with the reef mound, so that form the rimmed system of platform margin. The range of intra-platform bottomland diminish, while the range of grain bank expand. The patch reefs deposit in the higher sedimentary topography or previous grain bank. In the parasequence sets 8 to 9, the differentiation of sedimentary topography is obvious, and the uplift of reef-bank complex alternatively distribute with the lower interbank sea. The intra-platform bottomland distribute among the inherited deposit range of patch reef and grain bank in the open platform, and their sedimentary range become maximum in this period. The sedimentary cycle of patch reef and grain bank are 1 to 2, and the thickness is about 50 m to 100 m. The width of platform margin is 4 km to 14 km, and the length is 210 km. The range of T54 well to T78 well deposit lots of reef mound, and the range of T54 well to Z19 well deposit the carbonate mud mound. The granule shoal deposit widely, and it stacked with reef longitudinally form 1 to 2 sedimentary cycle, which the thickness is about 100 m to 200 m. The rimmed platform become a pattern essentially. In the parasequence sets 10, the accretion rate of accommodation is equal to the rate of sedimentation. The open platform mainly deposit the grain bank and interbank sea, and the range of interbank sea diminish apparently. The patch reef only deposit in local area like T77 well、T35 well. The range of platform margin diminish between the Z162—Z4—T62 well to the Tazhong NO.1 fault. Its width is 1 km to 12 km, and the length is about 100 km. It mainly deposit the granule shoal and interbank sea, the reef only deposit in local area. In this period, the depositional topography between platform margin and open platform appear apparently high low differentiation, so the rimmed platform is mature and formalized.