High-resolution variation in ostracod assemblages from microbialites near the Permian-Triassic boundary at Zuodeng, Guangxi region, South China

Abstract

After the end-Permian mass extinction (EPME), the marine environment was considered extremely toxic, mainly due to anoxic and high-temperature conditions and ocean acidification; consequently, the ecosystem contained few organisms. This paper describes a new ostracod fauna from the microbialite-bearing Permian-Triassic (P-Tr) strata at Zuodeng, Guangxi region, China. One thousand and seventy ostracod specimens were extracted from forty-eight samples. Fifty-three species belonging to fourteen genera were identified. Ostracods, primarily from the family Bairdiidae, were extremely abundant in the microbialites, which suggests that ostracods were opportunists that could survive the EPME within this special microbial ecosystem with sufficient food and scarce competitors and predators rather than undergoing a rapid and early recovery after the EPME event. Ostracods having simultaneous Paleozoic and Meso-Cenozoic affinities coexisted in this fauna. The similarities and differences among the ostracod faunas in the microbialite sections of the P-Tr boundary around the Paleo-Tethys indicate that there was a long-distance dispersal of ostracods, but the faunas maintained endemism at the species level. Previous studies have regarded microbialites as whole units, and it is difficult to detect environmental changes within a microbialite interval based on paleoecological groups of (super)families. In this study, high-resolution sampling was applied to identify changes in the ostracod abundance, diversity, assemblages and proportion of five dominant species in the section, which exhibited an evolutionary trend from the “Bairdia” group to the “Liuzhinia antalyaensis-Bairdiacypris ottomanensis” group. Furthermore, the transition of the ostracod fauna could be divided into six stages according to changes in the dominant species groups, suggesting that the microbialite environment was not entirely monotonous but fluctuated during the postextinction interval.