MISS in Mesoproterozoic Nonstromatolitic Limestones: A Case Study of the Third Member of Gaoyuzhuang Formation at Qiangou Section in Beijing

The Precambrian carbonate rocks are commonly characteristic of stromatolitic carbonate succession. However, in the western segment of Yanshan area, the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section in Yanqing, Beijing, is made up of a set of particular limestone succession with the sparseness of stromatolites. This limestone succession has been defined as the nonstromatolitic carbonate succession, which is a typical example in which three third-order sequences can be discerned according to the cyclicity reflected by successions of sedimentary facies. Within these third-order sequences, there are many subtidal carbonate cycles made up of both the medium- to thin-bedded aphanitic micrites and the thin-bedded marls in the transgressive and the early high-stand system tracts, and many grotesque sedimentary structures are widespread in the bedding planes of aphanitic micrites. These sedimentary structures, including the domal structure, the irregular reticular and chaotic tepee ridges, and the palimpsest ripple, make up an association of the microbial-induced sedimentary structure (MISS). Therefore, both the special MISSs and the particular lithological types make the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section to become the representative of the Precambrian nonstromatolitic carbonate succession. More importantly, this succession was formed during the golden age of stromatolite and could provide useful information for the further understanding of the evolving carbonate world of the Precambrian.