摘要： 快速海进页岩的特征及形成机理是细粒储层地质学研究的重点之一。地震层位追踪、连井地层对比、X衍射全岩分析、总有机碳测试和场发射扫描电镜分析表明,川南地区五峰组—龙马溪组快速海进页岩位于龙马溪组最底部,对应于笔石带LM1。该页岩石英平均含量49.3%(其中黏土级石英含量85%),方解石平均含量10.5%,白云石平均含量8.4%,黏土矿物平均含量23.4%。向盆地方向,石英含量增加,黏土矿物含量降低。快速海进页岩形成于相对海平面快速上升阶段,页岩厚度0.5~2.8 m,由盆地边缘向盆地中心逐渐增厚。页岩平均TOC含量5.4%,由盆缘向盆地中心逐渐降低,纵向TOC含量剖面呈现4种叠置样式。该套页岩的矿物组成和厚度分布与沉积时期的快速海进、生物及火山作用密切相关。快速海进导致陆源供给减少,故页岩厚度较小; 生物及火山作用导致页岩以微晶石英为主,盆地中心厚度较大。该套页岩的高TOC含量与水体缺氧、低沉降速率和高初级生产力有关。水体缺氧导致有机质保存能力增强,低沉积速率可减弱有机质的稀释,而初级生产力高可增加有机质的供给。该套页岩TOC含量平面变化及叠置样式与水深有关。随着水深增加,有机质沉降过程中的降解和再循环增加,故TOC含量降低。同时,随着水深增加,沉积物可容空间增大,从而形成不同的TOC含量叠置样式。

关键词: 海进页岩, 分布模式, 富集机理, 五峰组, 龙马溪组, 川南地区

Abstract: The characteristics and formation of the MF(maximum flooding)black shale are one of the focuses of fine-grained reservoir geology research. Seismic interpretation,well correlation,X-ray diffraction whole rock analysis,total organic carbon(TOC)test and field emission scanning electron microscope analysis show that the MF black shale of the Longmaxi Formation in the southern Sichuan Basin is in the basal part of the Longmaxi Formation,corresponding to the graptolite belt LM1. The shale has an average content of 49.3% quartz(85% clay-sized),10.5% calcite,8.4% dolomite and 23.4% clay minerals. The quartz content increases while the clay mineral content decreases basinward. The MF black shale formed during the stage of rapid relative sea level rise,with a thickness of 0.5-2.8 m and gradually thickening basinward. The average TOC content is 5.4%,which exhibits a gradual decrease towards the basin and forms four distinct stacking patterns in the vertical TOC content profile. The mineral composition and thickness distribution of the shale are closely related to the rapid transgression,biology and volcanism during the sedimentary period. The rapid transgression has led to a decrease in terrestrial sediment input,resulting in a reduction in shale thickness. Additionally,biological activity and volcanic influences have resulted in a prevalence of microcrystalline quartz and an increase in shale thickness towards the basin. The high TOC content of this shale is related to anoxic water,low sedimentation rate,and high primary productivity. Anoxic water body enhances preservation of organic matter. Low sedimentation rates can weaken the dilution of organic matter,while high primary productivity can increase the supply of organic matter. The planar variation and stacking style of TOC content in this set of shale are related to water depth. With increasing water depth,there is an amplified degradation and recycling of organic matter during sedimentation,leading to a decline in TOC content. Simultaneously,as the water depth rises,the sediment accommodation space also increases,resulting in distinct stacking patterns of TOC content.

Key words: transgressive black shale, distribution pattern, enrichment mechanism, Wufeng Formation, Longmaxi Formation, southern Sichuan Basin

中图分类号: 

• P512.2