Microbially induced sedimentary structures from the Xinji Formation (Cambrian Series 2), Western Henan, North China

Abstract

Abundant well-preserved microbially induced sedimentary structures (MISS) are exposed in the Xinji Formation, the earliest Cambrian sedimentary unit in North China. The MISS herein are categorized into microbial mat growth structure (wrinkle structures and mat biolaminites) and microbial mat destruction structure (sand cracks and 'Manchuriophycus' structures). The MISS developed on the surface of thick quartz sandstones, as well as the lithologic interface between thin sandstone and mudstone. Most of the sand cracks lack the direct evidence of microbial activities, whereas the mat biolaminites that consist of filamentous mica, clay minerals, and quartz grains may record the in situ microbial mats. The Xinji Formation deposited along with the Cambrian explosion when biodiversity and abundance of metazoan stayed relatively low. Besides, the intermittently exposed tidal flats are not the ideal place for early life, which exacerbated the ecological vacuum therein. The massive occurrence of the MISS in the siliciclastic rocks of the Xinji Formation indicated that the tidal flat setting during this period was still beneficial for accumulations of microbial mat because of the deficient grazing metazoans and weak bioturbation.

Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition

“…Furthermore, such taxa were not preferentially impacted during the White Sea-Nama extinction. Sedimentological evidence suggests that shallow marine environments characterized by organic mats were present during the Nama assemblage (4,26) and likely continued into the early Cambrian (9,27). Thus, these habitats were still available long after this event.…”