羌塘盆地中部上三叠统“甲丕拉组”沉积演化及研究意义

Sedimentary Evolution of the Upper Triassic Jiapila Formation at the Middle Qiangtang Basin and its Geological Significance

通过区域对比,根据岩石类型及其组合(岩性、颜色、层型、颗粒类型)、沉积旋回垂向序列、地质体几何形态、层内和层面的结构构造特征及其变化、生物类型及其组合、自生矿物和地球化学等相标志,将羌塘盆地中部甲丕拉组沉积相划分为大陆相区的洪积相、河流相,过渡相区的三角洲相和海洋相区的潮坪相、局限海台地相、沿岸沙坝相、火山喷发相和台地边缘浅滩相等9种类型,由沉积相组合总结了沉积相分布模式;在局限海台地相中发现了Quemocuomegalodon sp.和Neomegalodon cf.ampezzanus(Hoernes)化石及石膏矿点,石膏岩薄片中常见有重晶石和土状萤石等伴生,暗示该组局限台地相中有寻找沉积型重晶石、天青石、萤石和钾盐等矿产的潜力;同时由生物和沉积特征推断当时为半封闭较局限的干燥炎热浅水环境;该资料为区内及邻区认识与对比印支运动阶段"构造域"的转换提供了重要信息。

Based on the facies marks including sediment-style and assemblages（lithology,color,strata type,grain type）,vertical depositional features,fabric and construct characters,and biotic assemblages as well as authigenic mineral and geochemical characteristics,9 types of sedimentary facies in the Jiapila Formation within Yangtze source region can be recognized：pluvial facies,fluvial facies,detal facies,tidal flat facies,subtidal facies of restricted platform,longshore bar facies and volcanic eruption facies,as well as platform marginal facies.The bivalves fossil of Quemocuomegalodon sp.and Neomegalodon cf.ampezzanus（Hoernes） as well as gypsum deposit were discovered in the restricted platform.Moreover,barite,fluorite and other minerals were found in the gypsum deposition;therefore,all of these suggest that the deposit of lazurite,barite and fluorite are the prospecting potential in the restricted platform facies.The biologic features and sedimentary characteristics of the Jiapila Formation suggest that it was sedimented in shallow-water environment with high rate of evaporation.The new data on the sedimentary facies of the formations provide important information to understand the regional tectonic-paleogeographic environment during the Indosinian movement.