Abstract: A set of rudist bioherms is developed in the Upper Cretaceous Yigeziya Formation in the front area of the Kunlun Mountains in the southwestern part of the Tarim basin.Laterally it stretches like a string of beads for about 300km from west to east along the line linking Akecheyi ,Wuyitag,Yigeziya,Tuyeloke,Artashi and Momoka.The bioherm base is marked by well-developed source rocks-algal mi-crite-in the lower part and a bioclastic shoal in the upper part,the bioherm core consists of clustered rudist limestone,and onlap may be observed at the algal-mat top.Both the underlying rocks and covers of the bioherms are gypseous mudstone,thus forming a trap.