川北山前带寒武系筇竹寺组富有机质页岩发育模式

Developmental models of organic-rich shales in the Cambrian Qiongzhusi Formation in the piedmont zone of northern Sichuan Basin

张明何 魏祥峰 高波 戎佳 刘珠江 燕继红 杨琪航 王佳乐 刘慧萍 游浪 刘自亮

Minghe ZHANG Xiangfeng WEI Bo GAO Jia RONG Zhujiang LIU Jihong YAN Qihang YANG Jiale WANG Huiping LIU Lang YOU Ziliang LIU

研究川北山前寒武系筇竹寺组富有机质页岩分布、主控因素及沉积模式，对该地区页岩气勘探具有重要意义。利用野外地质调查、钻井和岩心资料，结合岩石薄片鉴定、全岩X射线衍射分析、总有机碳含量（）测定等分析测试资料，研究川北山前带筇竹寺组富有机质页岩的沉积模式、分布及主控因素。研究表明：①筇竹寺组页岩主要为强脆性硅质页岩和中等脆性硅/黏土混合质页岩，根据总有机碳含量（）—沉积构造—矿物组分将其划分为16种岩相类型川北山前带寒武系筇竹寺组页岩主要为富有机质纹层状强脆性硅质页岩相、富有机质层状强脆性硅质页岩相和含有机质层状强脆性硅质页岩相。其中前两类岩相为页岩气主要勘探开发岩相；②富有机质页岩普遍高于2 %，富有机质页岩具南厚北薄、西厚东薄分布的特征，有机质丰度具南高北低、西高东低的特点；③拉张槽及区域内隆-凹相间的古地理格局是筇竹寺组富有机质页岩差异分布的主要原因，区内不均衡构造演化加剧了页岩的非均质性展布；繁盛发育的低等浮游生物及细菌等提供了丰富的有机质来源，早期快速海侵下缺氧的深水环境利于有机质的保存，晚期摩天岭古陆和汉南古陆的持续隆升对有机质富集起抑制作用；④海平面升降和古气候演变控制了富有机质页岩在纵向上呈旋回性分布。

Investigating the distributions， dominant controlling factors， and sedimentary patterns of organic-rich shales in the Cambrian Qiongzhusi Formation in the Micang-Daba piedmont zone of the northern Sichuan Basin holds great significance for shale gas exploration within. Based on data from field geological surveys， drilling， and core observation， as well as analytical and test data derived from rock thin section observations， whole-rock X-ray diffraction （XRD） pattern， and total organic carbon （） content determination， we explore the sedimentary patterns， distributions， and dominant controlling factors of organic-rich shales in the Qiongzhusi Formation， piedmont zone of the northern Sichuan Basin. The results indicate that shales in the Qiongzhusi Formation consist primarily of highly brittle siliceous shales and moderately brittle silica-clay mixed shales. In terms of their content， sedimentary structures， and mineral components， these shales can be categorized into 16 lithofacies types， with the organic-rich laminated siliceous shale facies of high brittleness， organic-rich bedded siliceous shale facies of high brittleness， and the organic matter-bearing bedded siliceous shale facies of high brittleness dominating. The former two dominant shale facies are identified as the primary targets for the exploration and production of shale gas. The organic-rich shales， with content typically exceeding 2 %， are thicker in the south and west but thinner in the north and east， corresponding to a higher organic matter abundance in the south and west and lower abundance in the north and east； The intracratonic sag and the paleogeographic patterns exhibiting alternating uplifts and sags within are identified as the primary causes of the differential distribution of organic-rich shales in the Qiongzhusi Formation. The imbalanced structural evolution in the zone enhances the heterogeneous distribution of shales. The flourishing lower plankton and bacteria serve as substantial sources of organic matter. The anoxic deep-water environment under rapid transgression in the early stage creates favorable conditions for the preservation of organic matter， whereas the continuous uplift of the Motianling and Hannan oldlands in the late stage inhibits the organic matter enrichment. The eustatic movements and paleoclimate evolution govern the vertical cyclic distribution of organic-rich shales.

10.11743/ogg20240407