川北米仓山地区灯影组微生物碳酸盐岩发育特征

Characteristics of microbial carbonate rocks in Upper Sinian Dengying Formation of Micang Mountains,North Sichuan,China

四川盆地北部上震旦统灯影组是天然气的重点勘探层位。应用沉积学理论,参考微生物岩研究最新进展,以川北米仓山地区杨坝灯影组剖面为研究对象,通过剖面实测、薄片鉴定,发现灯影组白云岩中发育大量球状蓝细菌、丝状蓝细菌。前者形成了房室型、树枝型、链球型蓝细菌集合体;后者形态可分为管型、叠层型、凝块型。岩石学特征研究揭示蓝细菌参与到碳酸盐岩的沉积和成岩作用中,形成了叠层石、凝块石、团块、核形石,并对砂屑进行了局部钻孔改造。这些微生物形成了黏结型生物礁、骨架型生物礁,广泛发育在潮间-潮下带中。在此基础上,建立了微生物碳酸盐岩沉积模式。

The Upper Sinian Dengying Formation in the north of Sichuan Basin is the important natural gas exploration target. Based on the sedimentary theory, the late advances in the microbialites research and the studies of outcrops and thin sections, it is found that there are widespread coccoid cyanobacteria and filamentous cyanobacteria in the Upper Sinian Dengying Formation of Micang Mts. located in the north of the Sichuan Basin. The coccoid cyanobacteria form chambered, dendritic, and hammer-ball like morphology, whilst the later form tubal, stromatolithic and clotted shapes. The prokaryotic bacteria take part in the processes of deposition and diagenesis of carbonate rocks in the Dengying Formation to accommodate stromatolites, thrombolites, aggregates and oncolites, and in particular to bore to the intraclasts. The microbes build the frame microbial reefs and agglutinated microbial reefs widely developed in intertidal and subtidal environments. Accordingly, the sedimentary model of microbial carbonate rocks is established.