陇东地区延长组细粒沉积物特征

Characteristics of Fine-Grained Sedimentary in Yanchang Formation in Eastern Gansu Province

在大量钻井、测井资料的基础上,采用岩心分析、地球化学测试等方法,从湖泊演化过程中水体盐度、氧化还原条件、生产力变化及地球化学特征等方面,对鄂尔多斯盆地陇东地区细粒沉积物特征、分面规律及其主控因素进行了研究,取得的主要认识有:鄂尔多斯盆地陇东地区延长组长7段沉积期,气候温暖潮湿,半深湖-深湖大面积分布,富有机质细粒沉积物发育,该期形成的富有机质页岩主要受湖盆底形、砂体沉积模式的影响。尤其长73亚段沉积期为细粒沉积物主要发育期,快速湖侵,湖水深度和范围急剧增加,湖泊表层水体与底层水体存在盐度分层,形成大面积缺氧环境,有利于大规模发育富有机质页岩。深湖区平缓地带,陆源碎屑供给不足,有机碳含量高,有机质类型好(以Ⅰ、Ⅱ型为主),半深湖区斜坡带发育物源来自于陆地的粉砂质泥岩,干酪根以Ⅱ型为主,同时发育Ⅲ型干酪根。

Based on the drilling and logging data,this paper comprehensively analyses the distribution rule and major controlling factors of the fine-grained system in Eastern Gansu in Ordos Basin from such aspects as the enrichment mechanisms of organic matter,the changes of salinity,redox condition and productivity through core description and geochemical test.The results show that during the deposition of the Chang 7Member,mainly developed in this area were semi-deep to deep lakes with warm and moist climate,which is the advantageous sedimentary enviorenment for organic-rich shale mainly controlled by the sandbody architecture and the shape of lake basin.During the deposition of the Chang 73 Member,depth and scope of the lake sharply increased with water invading rapidly.The salinity difference between the circulation between upper surface water and lower water in the deep lake resulted in the formation of large-area anoxic environment in the deep lake,which is favorable for the development of organic-rich shale.In silent deep-flat lake that is far away from the delta front and in short of material supply,organic-rich shale was well developed,with high organic carbon content and mainly typeⅠ andⅡ kerogen.In slope semi-deep lake close to the delta front with sufficient material supply,wavy-massive silty mudstone was developed,mainly with typeⅡ and Ⅲ kerogen.