While marine biodiversity decreases, the ocean system is experiencing great changes, including sea surface temperature rising ( Seager etВ al., 2019), dissolved oxygen concentration declining ( Breitburg etВ al., 2018), and seawater acidification ( Ishida etВ al., 2021). Thus, it has been suggested that Earth might be entering the sixth mass extinction ( Ceballos etВ al., 2017 Cowie etВ al., 2022). Current declines of biodiversity were about 1,000 times the background rate of extinction throughout geological time ( Pimm etВ al., 2014), which may approach or exceed the magnitude of previous extinction events ( Ceballos and Ehrlich, 2018). They occurred five times in the past 600 million years (Myr) of EarthвЂ™s history, known as the вЂњBig Five,вЂќ each resulting in the loss of 75%вЂ“96% of marine species biodiversity ( Raup and Sepkoski, 1982 Erwin etВ al., 2002 Rong and Fang, 2004 Fan etВ al., 2020) and alteration of ecosystem structures ( Aberhan and Kiessling, 2015). Mass extinctions were defined as the substantial increase in loss of taxon during a relatively short interval of geologic time, in other words, extinction rates significantly above background levels ( Raup and Sepkoski, 1982 Sepkoski, 1986 Hallam and Wignall, 1997). Our study is an example of the wider debate about biotic response to rapid environmental change for both the PermianвЂ“Triassic transition and modern days. Thus, anoxic conditions might be the main cause of the PTME at deeper-water settings. At the Early Triassic mudstone with bottom-water settings in Chibi, the appearance of abundant small pyrite framboids (diameters of 4.74вЂ“5.96 Ојm), an indicator of intensified oxygen deficiency, was simultaneous with the two-step reduction of benthic diversity and abundance. The early Triassic transgression prompted some small foraminifers to migrate back to original platforms and flourish briefly as disaster forms. A plausible survival strategy for small-sized foraminifers was to migrate to deeper water to avoid extreme heat in shallow water. At the first pulse, large foraminifers were prominent victims in both shallow- and deeper-water settings. Benthic abundance in Chibi reduced by two steps at the two claystone beds (Beds 10 and 18): bioclastic content dropped from an average of 50% in Beds 1вЂ“9 to 10% in Beds 11вЂ“17 and then to less than 5% in Beds 19вЂ“23, suggesting a two-pulse extinction. Whereas for the fauna in Chibi, the benthos was relatively abundant (20%вЂ“55%) with more trace fossils and lacking calcareous algae. The end-Permian regression, marked by a karst surface, provided a plausible explanation for this extinction pattern. At Chongyang, abundant benthos (over 80%), including rugose corals, fusulinids, calcareous algae, and large foraminifers, disappeared precipitously at the topmost of Changxing Formation grainstone, which suggested complete damage of the benthic ecosystem, confirming a sudden single-pulse extinction pattern. We here investigated fossil assemblages and sedimentary microfacies on high-resolution samples from two adjacent sections of the South China Block: Chongyang from shallow-water platform and Chibi from deeper-water slop. The divergent patterns of PermianвЂ“Triassic mass extinction (PTME) have been extensively documented in varying water depth settings. 5Institute of Cultural Heritage, Shandong University, Qingdao, China.3 Institute of Geological and Mineral Resources Survey of Henan Geological Bureau, Zhengzhou, China

3School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan, China.2Key Laboratory of Environment Change and Resources Use in Beibu Gulf (Nanning Normal University), Ministry of Education, Nanning, China.

1Institute of Marine Sciences, Guangdong Provincial Key Laboratory of Marine Disaster Prediction and Prevention, Shantou University, Shantou, China.

Guoshan Li 1,2,3*, Yongbiao Wang 3вЂ , Sheng Li 3,4, Tan Wang 3, Wei Liao 5, Baozhu Deng 3 and Zhongping Lai 1*

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