New study of microbial mats from the Mesoproterozoic Jixian Group, North China: Evidence for photosynthesis and oxygen release.

• Microbial mats from the Jixian Group, North China were systemically investigated and three types of them were recognized. • Five kinds of sedimentary structure which were built by or related to microbial mat were recovered. • Bottleneck structures and bubble structures have been recovered and studied for the first time. Microbial mats were well established and widespread during the Proterozoic eon, playing a pivotal role in atmospheric oxygen content. In this study, microbial mats were systematically investigated from the 1600 Ma to 1400 Ma Jixian Group, North China. Three types of microbial mats were recognized, including Microbial Mat dominated by Filaments (MMF), Microbial Mat dominated by Coccoids (MMC), Microbial Mat dominated by Filaments and Coccoids (MMFC). These microbial mats were mainly built by Siphonophycus kestron , Siphonophycus solidum , Myxococcoides sp. and Coniunctiophycus majorinum. Due to in situ preservation, five sedimentary structures related to photosynthesis and oxygen release were discovered in these microbial mats. The alternating light-dark laminae and bottleneck structure may be caused by immediate mineralization and phototropism of filaments in a hypersaline environment. Bubble structure, fenestrae structure and hourglass structure probably were related to oxygen release, and their emergence fill the gap between oxygenic photosynthesis of microbial mat and atmospheric oxygen content in Proterozoic eon. [ABSTRACT FROM AUTHOR]