四川盆地磨溪—高石梯地区下寒武统龙王庙组颗粒滩特征及分布规律

以四川盆地磨溪—高石梯地区下寒武统龙王庙组颗粒滩为研究对象,结合钻井、测录井、岩心和薄片等资料,对龙王庙组颗粒滩特征、分布规律和主控因素进行了综合分析。研究区内颗粒滩岩石类型主要有两类:一类为具有明显颗粒结构的颗粒云岩,以砂屑云岩或鲕粒云岩为主;另一类为具有残余颗粒结构的晶粒云岩。颗粒滩主要发育向上变浅、粒度变粗的沉积序列,垂向上,与下部细粒沉积物可构成滩间海—颗粒滩、局限潟湖—颗粒滩等沉积相序;横向上,颗粒滩连续性较好,具有大面积连片分布的特征,自西北—东南向发育程度呈逐渐增大的趋势。进一步分析后认为,海平面的相对变化和沉积水体能量高低决定了龙王庙组颗粒滩的发育特征和叠置样式,不同级次海平面的升降变化使颗粒滩发育层位和发育程度得以定型,而沉积时期的古地貌则最终决定了龙王庙组颗粒滩平面分布的差异性。

Characteristics and distribution of grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area,Sichuan Basin

In this paper,the authors focused on grain bank of the Lower Cambrian Longwangmiao Formation in Moxi-Gaoshiti area,Sichuan Basin. Combined with abundant materials,such as drilling and logging data,cores and thin sections,the characteristics,distribution and its major controlling factors of grain bank in the Longwangmiao Formation were synthetically analyzed. There are two main rock types of grain bank in research area,one is grain dolostone with obvious granular structure,which is dominated by dolarenite and oolite dolostone,and the other is crystal grain dolostone with residual granular structure. Grain bank mainly has upward shallowing and granularity coarsening sequences,and could constitute sedimentary sequences of interact bank sea-grain bank and restricted lagoon-grain bank with lower fine-grained sediment in the vertical direction. In the lateral direction,grain bank has good continuity and is characterized by continuous distribution in a large area. On the plane,the development degree of grain bank increases gradually from northwest to southeast. Further analysis shows that the development characteristics and superimposed pattern of grain bank in the Longwangmiao Formation were determined by the relative sea-level change and sedimentary energy variation,the development horizon and degree of grain bank were formed by different grades of sea level fluctuation,and thepalaeogeomorphology finally determined the difference of planar distribution of grain bank during the depositional period of Longwangmiao Formation.