Basal Cambrian Microfossils from the Yangtze and Tarim Blocks
Our study confirms the occurrences the characteristic basal Cambrian AsteridiumComasphaeridiumHeliosphaeridium (ACH) small acanthomorphic acritarch assemblage in these two formations. These acritarchs include abundant Heliosphaeridium ampliatum (Wang, 1985) Yao et al., 2005, rare Comasphaeridium annulare (Wang, 1985) Yao et al., 2005, and a new acritarch form of moderate abundance. In addition, these basal Cambrian successions also contain clustered coccoidal microfossils, several filamentous cyanobacteria [Cyanonema, Oscillatoriopsis, and Siphonophycus], and the tabulate tubular microfossil Megathrix longus L. Yin, 1987. Some of these taxa (e.g., H. ampliatum, C. annulare, and M. longus) have a wide geographic distribution but occur exclusively in basal Cambrian successions, supporting their biostratigraphic importance. Comparison between the stratigraphic occurrences of microfossils reported here and skeletal animal fossils published by others suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.