COLLAPSE AND RECONSTRUCTION OF MARINE COMMUNITIES OVER THE PERMIAN-TRIASSIC TRANSITION: PALEOECOLOGICAL ASSESSMENT OF THE END-PERMIAN MASS EXTINCTION AND SUBSEQUENT RECOVERY

The Permian-Triassic (P-Tr) transition witnessed the most devastating biotic crisis in Phanerozoic history and drastically altered the balance of the biosphere and its subsequent evolution. This biotic crisis has been well demonstrated by numerical data of taxonomic changes. Recent studies also reveal that this event has resulted in severe ecological collapse and degradation. The ecologic method has also been treated as a very important measure of biotic recovery following this event. Collapse and subsequent restoration of marine communities and effects of the P-Tr environmental perturbations on community structure are still being deciphered despite several past studies. As a result, this study aims to assess the P-Tr ecological crisis and subsequent recovery by analyzing marine communities throughout the Changhsingian to Middle Triassic interval. Here, we analyze 60 Changhsingian shelly communities, 70 Early Triassic communities and 20 Middle Triassic communities from 26 outcrop sections exposed in South China based on our recently obtained field data and these published by Yin et al. (1995). Diversity indices (i.e. Dominance, Shannon and Simpson indices, Equitability and Fisher alpha) were calculated using the paleontological statistical analysis package PAST. The variation curves of the Shannon indices evaluating the community diversity and Dominance and Equitability both evaluating the evenness of the communities appear consistent with carbon isotopic excursion curves which could be the proxies of either environmental perturbations or biomass changeovers during the P/Tr event and its aftermath. Other palaeoecologic parameters (i.e. extent of biotrubation, tiering, ichnofauna, benthic Bambachian megaguilds and biosedimentary structures) (Fraiser & Bottjer 2005) have also been utilized to indicate ecological crisis and subsequent recovery during the P-Tr transition.