Diversity and systematics of calcified cyanobacteria and associated microfossils in Cambrian Series 2 shallow-marine carbonates, Yangtze Platform, South China

Calcified cyanobacteria and associated microfossils were systematically investigated in 10 shallow-marine carbonate sections – reefal and non-reefal – from Cambrian Series 2 of the Yangtze Platform, South China. A total of 15 species in 10 genera of calcified cyanobacteria and 5 species in 3 genera of Microproblematica were identified, including 2 new species (Streptubularia robustus sp. nov. and Xianella mollis sp. nov.). Girvanella, Subtifloria, Razumovskia, Acuasiphonoria, Xianella, and Streptubularia are attributed to Oscillatoriales (cyanobacteria); Kordephyton, Bija, Hedstroemia, and Botomaella are attributed to Nostocales (cyanobacteria); Renalcis, Izhella, and Epiphyton are attributed to Microproblematica. This is the first report of Acuasiphonoria, Razumovskia, Subtifloria, Xianella, Bija, and Botomaella from South China, and it advances the fossil record of Acuasiphonoria from the Late Ordovician to the Cambrian Series 2. Comparisons indicate that these calcified assemblages from the Yangtze Platform show close resemblances to those of the Siberian Platform and North China. This establishes a global distribution of at least 15 genera of calcified cyanobacteria in the early Cambrian. These results support the view that cyanobacterial calcification was widespread in shallow-marine environments during the early Cambrian, suggesting significant links to paleo-oceanic and paleo-atmospheric conditions.