The fluctuating environment associated with the episodic biotic crisis during the Permo/Triassic transition: Evidence from microbial biomarkers in Changxing, Zhejiang Province

摘要

The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyano-bacteria and green sulfur bacteria, the base of the marine ecosystem, to highlight the episodic nature of both the environment and the biotic crisis during this critical period. At least two episodes of cyano-bacterial expansion are documented by 2-methylhopanes ranging from C_(28) to C_(32) in carbon number, indicative of the instable marine ecosystem and the fluctuant aquatic nutrients. Meanwhile, the index of 2-alkyl-1,3,4-trimethylbenzenes (biomarkers of green sulfur bacteria) and the ratio of pristane to phytane (Pr/Ph) witness the fluctuation of sedimentary environmental redox conditions. The above molecular evidence suggests the occurrence of highly fluctuating environmental conditions during the Tr/P transition, which is consistent with, and probably the cause of, the multi-phased biotic crisis and the prolonged faunal recovery.