渝东—湘西地区志留纪小河坝组层序岩相古地理特征及演化

通过对渝东—湘西地区野外露头及相关室内研究,分析了区内志留纪小河坝组沉积环境、层序特征、沉积相展布及其演化特征。将该区小河坝组划分为2个沉积层序,每个沉积层序都由海侵和高位体系域组成。以体系域为编图单元,采用体系域压缩法,编制了渝东—湘西地区小河坝组4张层序岩相古地理图,结果表明:更加精确真实地反映了海陆分布、物源方向及其演化过程,更好地反映了层序格架下的物质聚集分布规律。揭示出研究区早志留世小河坝期碎屑岩沉积的物质主要来自东南部的江南雪峰山隆起,沉积环境由东往西逐渐变深,三角洲平原位于湘西地区,三角洲前缘发育于渝东地区;碳酸盐台地发育于靠近黔中隆起的南部浅水区,沉积环境由南往北逐渐变深,深水陆棚沉积区位于宜宾—重庆一带,该新认识对于更准确地预测渝东-湘西志留系储集体的分布以及下一步油气勘探部署具有重要实际指导意义。

SEQUENCE-BASED LITHOFACIES AND PALEOGEOGRAPHY OF THE SILURIAN XIAOHEBA FORMATION IN EASTERN CHONGQING CITY AND WESTERN HUNAN PROVINCE

We analyzed the sedimentary environment,sequence characteristics,and distribution of sedimentary facies of the Silurian Xiaoheba Formation in eastern Chongqing City and western Hunan Province.The Xiaoheba Formation in this area is divided into two sedimentary sequences,each consisting of a transgressive and a highstand systems tract.Four sequence-based lithofacies and paleogeographic maps of the Xiaoheba Formation have been generated using systems tracts as a mapping units.The maps reveal facies distribution patterns,sediment sources,and their temporal variations.Clastic sediments in the Xiaoheba Formation mainly came from the Xuefeng Mountain to the southeast.The sedimentary environment gradually deepened from east to west.Delta plain facies were located in western Hunan Province,and delta front facies in eastern Chongqing.Shallow water carbonate platforms were developed in the Guizhou Uplift to the south,and the sedimentary environment gradually deepened from south to north.Deep-water shelf was located in the Yibin-Chongqing area.The new data are useful in estimating the Silurian petroleum reservoir in eastern Chongqing and western Hunan.