河北承德路通沟剖面寒武系层序地层划分

层序地层学是地层学研究中的第三次革命,其强调年代地层框架内的沉积相关系和地层结构。河北路通沟剖面寒武系地层连续,层序界面清楚而独特,沉积现象丰富,是进行华北地台寒武系层序地层划分的典型地点之一。该剖面岩相类型以泥晶灰岩、鮞粒灰岩及白云岩为主,发育潮坪相、颗粒滩相、缓坡相及陆棚相等沉积相。在新的年代地层框架下,依据沉积相的垂向叠加样式及其反映的长周期旋回特征,将路通沟剖面寒武系划分为9个三级层序,以第三统徐庄组组成的三级层序(TST+CS+HST)为界,整个沉积序列从混积潮坪相沉积变为缓坡型碳酸盐岩沉积,层序也从以"TST+HST"为主的沉积序列转变为以"CS+HST"为特征的淹没不整合型层序序列。芙蓉统中众多的叠层石生物丘暗示:寒武系末期贫乏骨骼的风暴海洋中微生物碳酸盐岩随后生动物辐射也在增加的特殊沉积现象。基于沉积相叠置方式及旋回特征对路通沟剖面寒武系的层序地层研究,将为探索华北地台东北部广泛分布的寒武系地层的层序划分提供一个典型的实例,为今后大范围的追索和对比提供更多的思考途径。

Sequence-stratigraphic division of Cambrian in Lutonggou section, Chengde City, Hebei Province

The third revolution of stratigraphy was that of sequence stratigraphy, which uniquely focused on analyzing changes in facies and characteristics of strata. Lutonggou section in Hebei Province, characterized by sequential strata, evident and special sequence boundary and an ocean of sedimentary phenomena, is favorable for the sequence-stratigraphic division of the Cambrian in the North China Platform. Lithofacies in this section principally consist of micrite,oolitic limestone and dolomite, and sedimentary facies include tidal-flat facies, beach facies, ramp facies and shelf facies. The Cambrian strata in Lutonggou section can be divided into 9 third-order sequences according to the characteristics of sedimentary facies stacking patterns and long-periodic cycle change under the new chronostratigraphic system. Cambrian depositional succession, that was bounded by the third-order sequence"TST+CS+HST"formed by Series 3 Xuzhuang Formation, changed from the mixed tidal flat to the ramp carbonate deposits. At the same time, the sequence type changed from the succession dominated by the"TST+HST"to the drowning unconformity dominated by the"CS+HST". Furthermore, abundant stromatolite bioherms suggest a special depositional phenomenon that the skeleton- poor stormy sea in the late Cambrian was marked by the increase of microbial carbonate together with the radiation of metazoan. The sequence stratigraphy research on the Lutonggou section of Cambrian strata based on the characteristics of facies superposition and cycling will give a typical example for the sequence stratigraphy division of widespread Cambrian strata in the northeast of North China Platform, and also provide more ideas for the widespread tracking and correlation.