Photozoan carbonate factory nourished by cyanobacterial bloom of the Cambrian Miaolingian: An example from the Wolongshan section in Shou county of Anhui procince, North-China platform
Abstract:Since there are lots of intricate and difficult problems having only conjectural answers, describing, characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums. Carbonate factory are actually refer to production system, its original define refer to the clear neritic marine environment with the depth less than 15 m in which assemble most of carbonate producers. In the later, a double subdivision of the shallow carbonate production system has been proposed according to the energy resource, i.e. the photozoan and heterozoan factories, which represent some conceptual advancement. Along with the further understanding of styles of carbonate precipitation, a threefold subdivision of the benthic carbonate production systems enriched with wisdoms on basis of the carbonate factory principle has been proposed on a geologic scale, i.e. (1) T-factory, in which the T is derived from tropical or “top-of-the-water-column”; (2) the C-factory, in which the C stands for cool-water or controlled precipitation; and (3) the M-factory, in which M represents microbial, micrite, or mud-mound. Two aspects of particularities characterize the carbonate factory of the Cambrian Miaolingian: the first is the photozoan, the second is the microbial (the nourished by cyanobacterial bloom); so it can be discerned two particular carbonate factories, i.e. the photozoan T-factory predominated by radial ooids that are induced by photosynthetic biofilms and the photozoan M-factory predominated by microbial reefs that are built by cyanobacterial mats and also occupied the shallow environments normally filled by the T-factory. The Gushan Formation of the Cambrian Miaolingian at the Wolongshan section in Shou county of Anhui province in southern North-China Platform makes up a third-order sequence bound by drowning unconformity that is marked by an upward shoaling succession from the shelf muddy shales of the condensed section to the oolites covered by microbial reefs (leiolites) of the forced regressive system tract. A sedimentary succession from a grain bank predominated by microbial radial ooids to a microbial reef predominated by leiolites constitute the forced regressive system tract of this third-order sequence. Within the dense and dark micrites making up the core and the cortex of radial ooids as well as the clump or clot among ooids there are high-density preservatation of filamentous Girvanella that is relatively certain to analogical to the modern cyanobacterium Plectonema, which demonstrate that these radial ooids are products induced by photosynthetic biofilms and further delegate a particular photozoan T-factory. Within the leiolites making up the microbial reef overlying the oolite that represent the photozoan T-factory, the high-density preservation of filamentous Girvanella that are more than one half of volume indicates that this set of microbial reefs represents a particular photozoan M-factory. Thus, a special evolutionary succession from a photozoan T-factory to a photozoan M-factory was formed in the calcite sea with the cyanobacterial bloom of the Cambrian Miaolingian under the atmosphere with the most high content of carbon dioxide and relative high content of oxygen. These observations and researches provide a rare example and a insight into the further understanding of a photozoan factory of microbial carbonates of the Cambrian Miaolingian that is formed by organomineralization tied to the cyanobacterial bloom, which is coincided with metazoan radiation benefited from the evolution of biomineralization.
