川南—黔北地区下志留统龙马溪组沉积相展布及演化

Distribution and evolution of sedimentary facies of the Lower Silurian Longmaxi Formation in southern Sichuan and northern Guizhou area

川南-黔北地区下志留统龙马溪组发育了一套富含有机质的页岩,属于浅海陆棚沉积环境,基于野外实测剖面和岩心观察,结合有机碳含量(TOC)以及测井资料等,对龙马溪组进行了详细的沉积相研究。根据岩性标志,沉积构造特征,古生物特征,地球化学特征,识别出龙马溪组浅海陆棚相,包括浅水陆棚亚相和深水陆棚亚相。并进一步划分出风暴层,砂泥质浅水陆棚,泥质浅水陆棚,灰泥质浅水陆棚,灰质浅水陆棚,浊积砂,砂泥质深水陆棚,泥质深水陆棚,灰泥质深水陆棚等微相。龙马溪组自下而上划分出SSQ1和SSQ2两个沉积旋回,整体显示出水体变浅的趋势,并控制富有机质黑色页岩储层的分布。SSQ1的TST中泥质深水陆棚微相是最有利页岩储层发育的有利相带。

Organic-rich black shale,which is formed in shallow shelf sedimentary environment,is widely developed in the Lower Silurian Longmaxi Formation in southern Sichuan and northern Guizhou area.Based on the data of field measured profiles,drill core observation,testing of organic carbon content(TOC),and logging results,the sedimentary facies of Longmaxi Formation has been studied in detail.According to lithology markers,logging facies,and characteristics of sedimentary tectonics,paleotology and geochemistry,we identified neritic shelf facies composed of shallow shelf subfacies and deepwater shelf subfacies.The neritic shelf facies can be divided into storm layer,shallow sandy and muddy shelf,shallow muddy shelf,shallow gray and muddy shelf,shallow gray shelf,turbidite deposit,deep sandy and muddy shelf,deep muddy shelf and deepgray and muddy shelffurtherly.The Longmaxi Formation can be divided into SSQ1 and SSQ2 sedimentary cycles,which indicate a sea-level falling and affect the distribution of organic-rich rservoir of black shale.The deepwater muddy shelf microfacies in TST of SSQ1 are the best shale reservoir.