Comparison of end-Ediacaran to earliest Cambrian microbialites in the Tarim Basin, China: Diversities and paleo-environment

The Ediacaran-Cambrian (E-C) transition represents a crucial interval in Earth's history， with profound biological and environmental changes. Microbialites provide crucial records of organism-environment interactions during this transition. Here， the terminal Ediacaran and early Cambrian microbialite types and their depositional environments in the Tarim Basin were analysed using optical microscopy， SEM (Scanning Electron Microscopy)， and Raman spectroscopy. Three types of microbialites (microbial laminite， stromatolite， and thrombolite) occur in both the Ediacaran Qigebulak Formation and the Cambrian Xiaoerbulak Formation. Moreover， thrombolitic laminite， Renalcis framestone， and foam spongy dolostone are identified in the Xiaoerbulak Formation. The Qigebulak Formation features upward energy-enhancing cycles from intertidal-subtidal to grain bank facies， while the Xiaoerbulak Formation records a sedimentary transition from restricted to open platform environments. Across this interval， microbialites exhibit: (i) a slight decline in microbial carbonate abundance， marked by reduced microbial laminite and increased thrombolite; (ii) increased microbial diversity， evidenced by more varied microbialite types and the preservation of more complex organic matter; and (iii) the emergence of calcified filaments in early Cambrian microbial laminites. These variations likely record microbial evolutionary responses to extrinsic paleoenvironmental changes. These findings are significant for those focusing on paleo-environmental evolution during the Ediacaran-Cambrian transition.