The Depostional Facies And Facies Models Of The Middle-Upper Ordovician Carbonate Rocks In The Southern Margin Of Taibei Uplift, Tarim Basin

Bioherms and shoals of platform-rim facies with favorable reservoir are well developed in the Middle-Upper Ordovician of Northern Tarim Basin and are the major targets of gas and petroleum exploration within Tarim Basin.In the present paper the sedimentology and paleogeography of the carbonate rocks in the Middle-Upper Ordovician of Southern margin of Tabei Uplift are studied by means of observations and analysises of the cores and thin-sections from 8 key wells in the area, and the following conclusions are drawn. They are:1. Limestone is the predominant rock type in the Middle-Upper Ordovician of Southern margin of Taibei Uplift, and may be divided into packstone-micrite, bioclastic limestone and limestones with other characteristics. Of them,the packstone-micrite is the most common. The Middle-Upper Ordovician formations are stable in the lateral extension, but change distinctly in their vertical succession. The Penglaiba Formation comprises mainly micrite and dolomite, the Yingshan Formation is made of brown-greyish calcarenite and beige-colored micrite. The Yrjianfang Formation is represented by light brown-greyish sparry bioclastic calcarenite and sparry oolite limestone with some intercalation of wackstone. The Tumuxiuke Formation is characterized by grey bioclastic micrite,brown nodular micrite,brown nodule-like micrite and fuchsia marl and mudstone. The lithologies of the Lianglitage Formation include grey nodule-like bioclastic micrite,thrombolite,reef limestone and bindstone, and muddy bands or laminations are common in the formation. And the Sangtamu Formation is characterized by a mixture of terrigenous detrital sediments and Carbonate deposition.2. Three facies zones may be recognized in the Ordivician of the Southern margin of Taibei Uplift. They are carbonate platform, platform margin-slope and shallow-marine shelf. And the 3 facies zones may be subdivided into 7 subfacies, including restricted platform, open platform,ramp that bears the reef knolls,submerged platform, platform margin, front platform slope and shallow-marin shelf. Six sedimentary stages may be distinguished in the Ordivician. Restricted facies is recorded in the Penglaiba Formation, open platform in the Yingshan Fromation, platform margin facies in the Yrjianfang Formation, submerged platform facies in the Tumuxiuke Formation, platform slope facies in the Lianglitage Formation, and shallow marine shelf facies in the Sangtamu Formation.3. Four typies of carbonate platforms may be distinguished in the Ordovician of the region. They are rimmed carbonate platform, ramp, submerged platform and distally steepened ramp. The rimmed carbonate platform is represented by the Yingshan Formation, ramp by the Yrjianfang Formation, submerged platform by the Tumuxiuke Formation, and distally steepened ramp by the Lianglitage Formation.