Sedimentary factories and ecosystem change across the Permian–Triassic Critical Interval (P–TrCI): insights from the Xiakou area (South China)

Abstract

The Permian–Triassic mass extinction included a potentially catastrophic decline of biodiversity, but ecosystem change across this event remains poorly characterized. Here we reconstruct sedimentary factories and ecosystem change across the Permian–Triassic Critical Interval (P–TrCI) in the Xiakou area (South China). Six microfacies (MF) were classified. The succession begins with a eukaryote-controlled carbonate factory (MF-1) that passes upward into an organomineralization-dominated carbonate factory (MF-2–3). Organic-rich marls atop these units reflect carbonate factory collapse (MF-4). Organomineralization-driven carbonate formation restarts prior to the Permian–Triassic boundary (MF-5) and subsequently develops into a mixed carbonate factory where organomineralization and biomineralization are almost equally important (MF-6). MF-1 reflects oxygenated shallow water environments. In contrast, MF-2–6 were all deposited in somewhat deeper environments, some of which episodically exhibited elevated salinities, oxygen depletion, and, possibly, euxinic conditions. Our results demonstrate that distinct changes in carbonate production styles, biodiversity, and environmental conditions are not synchronous at Xiakou. Furthermore, the Xiakou record is strikingly different to that of other localities, even from the same area (e.g., the Global Stratotype Section and Point section at Meishan). Together, these findings highlight the enormous complexity of the P–TrCI and calls simplified views of the Permian–Triassic mass extinction into question.

Ecosystem changes through the Permian–Triassic and Triassic–Jurassic critical intervals: Evidence from sedimentology, palaeontology and geochemistry

“…Section upwards, δ 13 C org generally shows a slightly increasing trend (Table 1; Fig. 9; Pei et al ., 2021, table 1, fig. 2).…”

“…2). As detailed below, the section mainly comprises grey to black limestones, intercalated with black mudstones (Pei et al ., 2021). Several volcanic ash beds/layers occur throughout the section (for example, beds/layers P 15‐1 , P 15‐3 , T 2 , T 4 , T 13 and T 15 ) (Fig.…”

“…This trend is only interrupted by bed P 5 , which shows a higher δ 13 C carb value of 2.4‰ (Table 1; Fig. 9; Pei et al ., 2021, table 2, fig. 10).…”

“…It is important to note that δ 13 C org values of P–T samples reported in this study are not identical to those reported in Pei et al . (2021) because they were re‐measured for this study.…”

“…The Meishan record comprises palaeontological evidence for two mass extinction episodes (ME 1 and ME 2) across the P–T boundary (Song et al ., 2013), which are correspondingly identified in the Xiakou section (Fig. 2; Pei et al ., 2021).…”