Clastic facies microfossils from the Chuanlinggou Formation (1800 Ma) near Jixian, North China

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Abstract
Abundant organic-walled microfossils are well preserved in petrographic thin sections of shales from the c. 1800 Ma old Chuanlinggou Formation (Changchengian System) near Jixian, North China. The microfossils are compressed parallel to lamination and consist of sphaeromorph acritarchs and filamentous forms. The sphaeromorphs, ranging from 20–200μm in diameter, are more abundant in shales of the base of the Chuanlinggou Formation and assignable to Kildinosphaera, Leiosphaeridia, and Chuaria. They could represent either prokaryotic or eukaryotic organisms. The filaments, 0.5–24μm wide, are apparently unbranched, non-septate, and originally tubular structures. They occur in shales of the upper part of the formation, and include Archaeotrichion, Eomycetopsis, and Siphonophycus. The wider filaments probably represent the empty sheaths of the Oscillatoriaceae, whereas the narrower ones could represent either oscillatoriacean filaments to bacterial filaments. Although the Chuanlinggou microbiota seems to be a highly biased sampling of the Proterozoic life toward degradation-resistant taxa, it is among the oldest clastic microbiotas now known.