川西南犍为地区下三叠统嘉陵江组沉积相及其演化特征

Sedimentary Facies and Their Evolution Characteristics in Jialingjiang Formation of Qianwei Area, Southwest Sichuan Basin

以岩心精细描述、薄片鉴定和测井曲线分析为基础 ,通过对川西南犍为地区嘉陵江组的岩石类型组合、古生物化石、沉积结构、沉积构造和沉积序列等沉积相标志的详细研究 ,结合区域沉积背景 ,认为犍为地区嘉陵江组为半局限海 -局限海台地沉积 ,进一步识别出混积潮坪、潮缘滩、半局限泻湖、局限泻湖和蒸发潮坪等 5种沉积亚相类型 ;在此基础上 ,通过连井沉积相横剖面对比和重点层段沉积相平面分布特征的研究 ,揭示出嘉陵江组的沉积相演化规律由下至上从混积潮缘到潮下低能 ,再到潮上蒸发环境 ,构成一个完整的海进—海退发展旋回 ;

Based on sophisticated observations on cores, thin sections and analysis on logging curves, combined with through study on sedimentary characteristics, such as lithologic types and associations, palaeobiologic fossils and textures, sedimentary structures, and considering regional sedimentary background, it is recognized that Jialingjiang Formation in Qianwei area is characterized by semi-restricted to restricted marine platform deposits.Five sedimentary subfacies could be subdivided: the mixing tidal flat subfacies, the peritidal bank subfacies, the semi-restricted subfacies, the restricted lagoon subfacies, and the evaporate tidal flat subfacies. With the above results, and through the study on facies correlation of three well sections and facies distribution of three key reservoir formations, it is pointed out that the sedimentary environment evolution of Jialingjiang Formation from the botteom upwards is from mixing deposit, Through subtidal deposit with low energy, to supratidal evaporate deposit. This history formed a complete developing cycle from marine transgression to regression. It is quite possible that the peritidal bank subfacies with grain rock type and evaporate tidal flat subfacies with dolomite rock type could be favorable reservoir layers.