川东南龙马溪组海相页岩纹层发育特征

Laminae Growth Characteristic within the Lower Silurian Longmaxi Marine Shale in the Southeast Sichuan Basin

纹层作为页岩最富特色的沉积构造,广泛发育于页岩层系中,对页岩储层有着重要的影响,但目前针对海相页岩纹层的研究较少。本文以川东南龙马溪组海相页岩为研究对象,通过岩心、薄片鉴定和扫描电镜等分析,对其纹层发育特征进行研究。结果表明:研究区龙马溪组一段页岩纹层按矿物组分划分,可识别出粘土纹层、石英纹层、碳酸盐岩纹层、云母纹层和黄铁矿纹层5类,按形态可识别出平行纹层、水平纹层、波状纹层以及斜纹层。综合纹层发育特征、沉积构造特征及矿物接触关系,可识别出粘土纹层–石英纹层互层、粘土纹层–碳酸盐互层、石英纹层–碳酸盐互层的三种二元结构类型,以及石英纹层–粘土纹层–碳酸盐岩纹层互层的三元结构类型。综合来看,研究区主要发育粘土纹层和石英纹层,并且纹层发育呈现出自下而上出现频率高–低–高的周期性变化,反映出不同时期的沉积环境具有变化特征。

As the most characteristic sedimentary structure of shale, the laminae are widely developed in shale strata, which have an important impact on shale reservoirs. However, there are few studies on laminae in the marine shale. Based on drilling core, thin section identification and scanning electron microscope (SEM), the characteristics of laminae within the Lower Silurian Longmaxi marine shale in the Southeast Sichuan Basin were investigated. According to the major mineral composition, five types of laminae are identified: clay laminae, quartz laminae, carbonate laminae, mica laminae and pyrite laminae. Based on the occurrence, parallel laminae, horizontal laminae, wavy laminae and twill laminae can be identified. Combining the laminae characteristics, the sedimentary structure and the contact relationship of the minerals, three kinds of dual laminae combination are identified: clay laminae-quartz laminae, clay laminae-carbonate laminae and the quartz laminae-carbonate laminae. In addition, there is a ternary type of laminae, which is quartz laminae-clay laminae-carbonate laminae. In general, the clay and quartz laminae were mainly developed in the study area. The laminae development shows a periodic change of high-low-high development frequency from bottom to the top, reflecting the change of the sedimentary environment in different periods.