河北承德寒武系凤山组叠层石生物丘中的沉积组构

Sedimentary Fabrics for the Stromatolitic Bioherm of the Cambrian Fengshan Formation in Chengde,Hebei

河北承德路通沟剖面芙蓉统凤山组中部发育厚层块状叠层石生物丘,构成一个淹没不整合型层序的强迫型海退体系域,指示这些叠层石形成于中高能浅海环境。该生物丘宏观上主要由柱状叠层石组成,叠层石内部纹层较粗糙,在构成叠层石的致密泥晶和微亮晶组构中,还见到球粒、底栖鲕粒及凝聚颗粒等多种生物成因颗粒类型,代表着复杂的微生物活动特征,以此而区别于前寒武纪的叠层石。更为重要的是,叠层石生物丘中的致密泥晶基质中发育一些"石松藻(Lithocodium)"状的钙化蓝细菌菌落残余物,以及一些丝状钙化蓝细菌化石,指示了形成叠层石的微生物席为蓝细菌所主导的微生物席。因此,凤山组叠层石生物丘内复杂而特殊的碳酸盐岩沉积组构为研究叠层石形成过程中复杂的微生物代谢活动所产生的钙化作用机制提供了一个宝贵的地质实例。

The stromatolitic bioherm in the middle part of the Furongian Fengshan Formation at the Lutonggou section of Hebei Province was masked by a bed of stromatolite bioherm,and formed forced-regressive system tract within three-order sequences of drowning unconformity type,which suggested the stromatolite developed in a medium-high energy coastal sea. Macroscopically,this bioherm consisted dominantly of columnar stromatolite with the ambiguous lamination. Microscopically,the bioherm was characterized by dense micrite and microspar,and it was well seen in bioherm that involved peloids,benthic oolites and aggregate grains,all of which represented complicated microbial activities,thus it differed from the Precambrian stomatolites. Furthermore,more lithocodium-like colonies of calcified cyanobacteria remnants and some filamentous calcified cyanobacteria fossils developed in the dense micrite matrix of the stromatolitic bioherm,and it demonstrated the microbial mats forming stromatolite were composed of mats leading by cyanobacteria. In general,the complicated and special carbonate sedimentary fabrics within stromatolitic bioherm of the Fengshan Formation provided a precious geological case for the understanding of complicated microbial metabolism in the growth of stromatolites.