Morphologic Association of Microbially Induced Sedimentary Structures As Paleoenvironment Indicator: An Example from Meso- to Neo-Proterozoic Siliciclastics of Southern North China Platform

Microbially induced sedimentary structures (MISS) are derived from the interaction of microbes and sedimentation by various geological processes, and have been studied more often as biosignature for early life, while their significance in paleoenvironmental analysis has not been adequately studied yet. Our study shows that the Ruyang (Pt₂) and Luoyu Groups (Pt₃) in the southern North China Platform are dominated by peritidal silisiclastics with abundant MISS, especially those related with mat destruction, and indicates that the morphologic variation and association of MISS are largely influenced by topography. The topography, to some extent, determines the hydrodynamics, substrate exposure duration and water supplement, and exerts influence on mat growth and their destruction, and in turn influence the morphology of MISS, especially in peritidal environments. From the subtidal to supratidal, four zones have been recognized, each of them with its own distinctiveness in MISS morphological association. The subtidal to lower intertidal zone is short of in situ MISS but has some redeposited mat chips, while the upper intertidal is featured by mat protected ripple marks and chips. The lower supertidal is rich in various MISS, especially sand cracks, for its low hydrodynamics, sufficient water supplement and frequently exposed environment, with thick mats, while the upper supertidal abounds smaller sand cracks than those in lower supertidal zone due to relatively thin microbial mats. Thus, Meso- to Neo-proterozoic MISS from the southern North China Platform show that the morphologic association of MISS can be used as good indicators for paleoenvironmental reconstruction.