西藏改则地区上三叠统日干配错组鲕粒滩相灰岩沉积特征及其环境意义

西藏改则地区上三叠统日干配错组发育了一套台地相碳酸盐岩沉积，在该套碳酸盐岩沉积中以存在大量鲕粒滩为特色。鲕粒滩可以进一步划分为开阔台地浅滩和台地边缘滩。鲕粒滩岩石类型分析表明，该套碳酸盐岩为镶边台地型沉积，开阔台地内浅滩为异地鲕和原地鲕混杂堆积，台缘浅滩鲕粒主要为原地鲕。台缘鲕粒滩为一个三级海侵体系域内部的次一级进积序列，具有潮下型米级旋回的特点，每层鲕粒滩相鲕粒灰岩的类型较为单一，大小均匀，各层鲕粒灰岩间鲕粒类型不同，具有从微晶鲕→放射鲕→同心鲕过渡的趋势，向上鲕粒粒径变大，沉积厚度明显增加。

Oolitic Limestone Sedimentary Characteristics and Its Environmental Significance of the Upper Triassic Riganpeicuo Formation,Gaize Area,Tibet

Upper Triassic Riganpeicuo Formation in Gaize area, Tibet, developed a set of platform facies carbonate sediments which are a characteristic of multi-layer oolitic beaches, and these multi-layer oolitic beaches could be further divided into open platform shoal and platform margin beach.Analysis of rock types showed that this set of carbonate sedimentary succession was formed in the fringe platform sedimentary environment and the intraplatform shoal developed melange of in situ and allogeneoolitic oolitics, while the platform margin beach developed mainly in situ oolitic. Platform margin oolitic beach was a subsequence of progradational sequences in three-order transgressive system tract, and had characteristics of subtidal type meter-scale cyclic. Each oolitic limestone layer was relatively single in type and uniform in size, and the oolitic type was different among the oolitic limestone layers which possessed the trend of changes from omicrite to radial, and to concentric ooides. The size of oolitic increased and sedimentary thickness increased markedly from lower to upper.