Sheet-like microfossils from hydrothermally influenced basinal cherts of the lower Cambrian (Terreneuvian) Niutitang Formation, Guizhou, South China

Early diagenetic cherts in basinal shales of the lower Cambrian (Terreneuvian) Niutitang Formation, exposed in the Yangtiao section, Majiang, Guizhou Province, South China, contain abundant sheet-like microfossils. The sheets are carbonaceous, rich in complex aromatic molecules, sinuously folded and, commonly, tightly enrolled. Their regular thickness, lack of evidence for cellular structure, occasional ornamentation by finger- or hair-like projections, and infrequent attachment to one another eliminate ripped up microbial mats and blade-like algae as biological sources. More likely, the Niutitang sheets represent surficial coverings of animals. In the absence of information on sheet morphology, it is difficult to constrain systematic interpretation further, but other Ediacaran and Cambrian fossils suggest that a cnidarian affiliation is plausible. The siliceous sequence of the lowest Cambrian Niutitang Formation was deposited under a relatively stable anaerobic environment, episodically influenced by hydrothermal fluids. Thus, it is probable that the sheets were transported into the basin from oxic shelves or sank to the bottom from oxygenated surface waters. In either event, these problematic remains provide new evidence of biological diversity in early Cambrian oceans.