Different triggers for the two pulses of mass extinction across the Permian and Triassic boundary

Abstract

Widespread ocean anoxia has been proposed to cause biotic mass extinction across the Permian–Triassic (P–Tr) boundary. However, its temporal dynamics during this crisis period are unclear. The Liangfengya section in the South China Block contains continuous marine sedimentary and fossil records. Two pulses of biotic extinction and two mass extinction horizons (MEH 1 & 2) near the P–Tr boundary were identified and defined based on lithology and fossils from the section. The data showed that the two pulses of extinction have different environmental triggers. The first pulse occurred during the latest Permian, characterized by disappearance of algae, large foraminifers, and fusulinids. Approaching the MEH 1, multiple layers of volcanic clay and yellowish micritic limestone occurred, suggesting intense volcanic eruptions and terrigenous influx. The second pulse occurred in the earliest Triassic, characterized by opportunist-dominated communities of low diversity and high abundance, and resulted in a structural marine ecosystem change. The oxygen deficiency inferred by pyrite framboid data is associated with biotic declines above the MEH 2, suggesting that the anoxia plays an important role.

Biotic Response to Rapid Environmental Changes During the Permian–Triassic Mass Extinction

“…A closer study of foraminiferal assemblage at the Liangfengya section revealed that foraminifers had two extinction pulses spanning the P-Tr boundary (Liu et al, 2020). Li et al (2021) also found two extinction levels among benthic organisms at the Liangfengya section.…”

“…On the other hand, among different paleogeographic settings, sharply different patterns of the same faunas had also been observed, typified by foraminiferal extinction (Song et al, 2009;Zhang and Gu, 2015;Li et al, 2021). The stratigraphic succession from the end-Permian to Early Triassic interval in the Chongyang section was very clear at the outcrop.…”

“…Multiple studies on PTME have been conducted in various paleogeographical settings (e.g., Jin et al, 2000;Shen et al, 2011;Song et al, 2012;Liu et al, 2020;Li et al, 2021), but many aspects of the extinction, including its pattern and triggers, have long been disputed. Jin et al (2000) proposed that the PTME occurred at the end-Permian as a single abrupt event based on 329 marine invertebrate species from the Meishan section in the South China Block (SCB).…”

“…However, the research on potential triggers of PTME could be affected indirectly by the uncertainty of the PTME process. Li et al (2021) recently proposed that the two phases of PTME had different environmental triggers in the Liangfengya section. Their data confirmed that oxygen deficiency was key in the second pulse of PTME; however, the first pulse might have been triggered by other environmental factors such as high and oscillating temperatures (Sun et al, 2012) rather than an anoxia event (Isozaki, 1997;Grice et al, 2005).…”

Two deep marine oxygenation events during the Permian-Triassic boundary interval in South China: Relationship with ocean circulation and marine primary productivity

“…Therefore, among the multitude of P-T studies in South China, investigations of marine redox conditions have been conducted by applying multiple methods to sedimentary sections that were deposited at different water depths and under various paleogeographic conditions (see literature in Table . 1). The array of intensive studies has resulted in important controversies on how to interpret the marine redox history through the P-T boundary interval (Bond and Wignall, 2010;Loope et al, 2013;Proemse et al, 2013;Xiao et al, 2018;Li et al, 2021;Xiang et al, 2021).…”