【摘要】 华北地台的寒武系苗岭统,大致包括毛庄组、徐庄组、张夏组和崮山组,这些组分别组成相应的三级沉积层序,在它们的顶部集中发育着鲕粒滩相灰岩而构成强迫型海退沉积,成为时间特化的相,代表着鲕粒主导的特别的寒武纪碳酸盐岩台地类型,表现在浅海陆架中大面积分布鲕粒滩,而且在这样的鲕粒滩中生长和发育着微生物碳酸盐岩主导的生物丘;河北省秦皇岛市驻操营剖面的张夏组上部鲕粒滩相灰岩中的生物丘正是上述现象最为典型的代表。虽然类似的现象曾经被描述为"藻坪"沉积,或者笼统地归为"微生物礁",但是,河北省秦皇岛市驻操营剖面的张夏组上部鲕粒滩相灰岩中的生物丘,以下现象不但将其特征化而且代表着壮观的沉积学现象:(1)在强迫型海退体系域的下部与鲕粒滩相灰岩交互产出的主要是柱状叠层石生物丘;(2)在张夏组顶部则以集中产出的均一石和树形石生物丘为特征;(3)下部的柱状叠层石生物丘中主要包括石松藻(Lithocodium)-孢网菌(Bacinella)状组构的钙化蓝细菌;(4)在上部集中产出的均一石与树形石生物丘,则发育着丝状钙化蓝细菌、基座菌(Hedstroemia)和附枝菌(Epiphyton)之类的多样化的钙化蓝细菌。由于石松藻(Lithocodium)-孢网菌(Bacinella)状组构的钙化蓝细菌是一种灭绝了的浅海生命形式,而且是不知道分类位置归属的生命形式,尤其是石松藻(Lithocodium)状组构近年来在寒武纪微生物碳酸盐岩研究中多被解释为"硅质海绵骨针的网状物"或"非骨针角质海绵骨骼纤维",再考虑到均一石自从命名以来很少描述在古老的地层记录之中,因此,驻操营剖面张夏组上部多样化微生物碳酸盐岩所主导的生物丘,以及生物丘中特别而且多样的钙化蓝细菌化石构成,为了解蓝细菌主导的光合作用微生物席复杂的钙化作用形成微生物碳酸盐岩提供了较为典型的实例。更多还原

【Abstract】 The Cambrian Miaolingian of the North-China Platform is chieflyconstituted by the Maozhuang,the Xuzhang,the Zhangxia and the Gushan Formations,and these Formations respectively make up the corresponding third-order depositional sequences.The time-specific facies represented by oolitic grainstones of the carbonate bank that is commonly makes up the forced-regressive system tract for each third-order depositional sequence also marks a special type of carbonate platform dominated by ooids,which is characteristic of the large-scale distribution with large acreage of oolitic-grainstone bank with the growth of bioherm dominated by microbial bioherms.Carbonate bioherms within the oolitic-grainstone bank at the Zhucaoying section in Qinhuangdao city of Hebei province can be considered as a typical example.Although similar deposits have described as the deposit of the "algal falt"deposit within the oolitic graonstone bank as well as grouped into the microbial reef,following features not only characterize the bioherm within the oolitic graonstone bank at the Zhucaoying section in Qinhuangdao city of Hebei province but also represent a grand sedimentological phenomenon:(1) massive and thick-bedded carbonate bioherms of the column stromatolite with the alteration of massive and thick-bedded oolitic grainstons of the carbonate bank are developed in the low part of the forced regressive system tract;(2) carbonate bioherms dominated by leiolites and dendralites are centralized in the top part of the Zhangxia Formation;(3) within column stromatolites are observed particular fossils of calcified cyanobacterias,i.e.the fossils belonging to the Lithocodium-Bacinella group;(4)several varieties of calcified cyanobacterias,such as the fossils of filamental cyanobacterias,the Hedstroemiaand the Epiphyton,are found within the carbonate bioherms dominated by leiolites and dendralites.Lithocodium and Bacinella are now extinct,shallow marine life forms of unknown taxonomic origin,which are frequently described in the Mesozoic strata.No examples of modern leiolite have been published,and a few examples are described in ancient stratigraphical records.More importantly,the depositional fabric that is similar to the Lithocodiumor the Lithocodium-like fabric is commonly interpreted as "the network of silicious sponge spiculas"or "the skeleton fibre of non-spicula keratose demosponges"during the study on the microbial carbonate of the Palaeozoic.Therefore,the bioherm dominated by microbial carbonates enriched with many varieties of fossils of calcified cyanobacterias in the upper part of the Zhangxia Formation at the ZHucaoying section is an important example for the further understanding of microbial carbonates resulted from the sophisticated calcification of microbial mats or biofilms.更多还原