Postdoctor WANG Jianguo and his teacher CHEN Daizhao focus on the chert successions across the marginal zone of the Middle Yangtze Platform near Dayong in western Hunan, South China.

All these data suggest that the marginal zone chert deposits resulted from a low-temperature, silica-rich hydrothermal system, in which the mounded chert was precipitated around the releasing vents, i.e. as silica chimneys. The vein and splayed brecciated chert, however, was formed along the syndepositional fault/fracture conduits that linked downward, while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor. These petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation; rapid tectonodepositional and oceanic changes during the Ediacaran–Cambrian transition in South China.

Fig. 1. Conceptual model showing the tectono-depositional setting for the development of hydrothermal venting fields and chert deposition on the terraced margin of the Yangtze Platform and further basinward, South China during the Ediacaran–Cambrian transition.(Image by WANG)

Wang et al. Petrology and geochemistry of chert on the marginal zone of Yangtze Platform, western Hunan, South China, during the Ediacaran–Cambrian transition. Sedimentology. 2012, 59: 809-829 (Download Here)