First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China

Organic-walled microfossils offer an important window onto the biospheric evolution in pre-Cryogenian and provide biostratigraphic implications for many Proterozoic fossiliferous sequences which are poorly age constrained for the lack of reliable radiometric date. Recently, macroscopic carbonaceous compression fossils have been reported for the first time from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China. However, organic-walled microfossils have never been discovered in the Shiwangzhuang Formation before. To improve our knowledge about Proterozoic biodiversity in North China, we conducted a micropaleontological survey on the argillaceous limestone samples of the Shiwangzhuang Formation, which also contain macroscopic carbonaceous compression fossils, from the Baishicun section in Anqiu, Western Shandong, North China. Our investigation shows that the Shiwangzhuang microfossil assemblage is dominated by smooth-walled sphaeromorphic acritarchs and...