河北秦皇岛驻操营剖面张夏组鲕粒滩叠层石生物丘特征及沉积环境

Characteristics and sedimentary environment of stromatolite bioherms in oolitic shoal of Zhangxia Formation in Zhucaoying Section,Qinhuangdao,Hebei

河北秦皇岛驻操营剖面寒武纪地层出露完整且连续,在苗岭统张夏组顶部发育叠层石生物丘。结合野外资料和镜下观察,分析研究区柱状(穹窿状)叠层石特征及沉积环境。结果表明:河北秦皇岛寒武系张夏组顶部强迫型海退体系域发育叠层石生物丘与高能鲕粒滩相灰岩,二者交互产出,代表华北地台寒武纪海平面缓慢下降过程的碳酸盐沉积。张夏组叠层石致密泥晶中可见保存较好的丝状钙化蓝细菌鞘化石及窗格状组构,揭示叠层石形成于光合作用微生物席或微生物膜复杂的钙化作用;可见少量与硫酸盐还原细菌诱发沉淀作用有关的黄铁矿残余物。该结果为研究寒武纪叠层石沉积环境提供实例。

The Cambrian strata of Zhucaoying Section in Qinhuangdao,Hebei are intact and continuous,and stromatolites are developed in the top of Zhangxia Formation of Miaoling Series.Based on field data and microscopic observation,the characteristics and sedimentary environment of columnar(domal)stromatolites are studied.The results show that stromatolite bioherms and high energy oolitic shoal limestones are developed in the forced regressive system at the top of the Cambrian Zhangxia Formation in Qinhuangdao,Hebei,which are produced in an interactive manner,representing the carbonate deposition during the slow sea level decline in the North China Platform during the Cambrian.The well-preserved filamentous calcified cyanobacteria sheath fossils and window-like fabrics can be found in the dense micrite of the stromatolites from the Zhangxia Formation,suggesting that the stromatolites were formed by the complex calcification of photosynthetic microbial mats or microbial membranes.A small amount of pyrite residue associated with precipitation induced by sulfate reducing bacteria was observed.The results provide an important case for studying the sedimentary environment of Cambrian stromatolites.