Abstract
The end-Permian mass extinction (EPME) was the most severe mass extinction event of the Phanerozoic, and was associated with the development of global oceanic anoxia. The intensification of ocean anoxia preceded the EPME, but the degree of intensity and timing of oceanic redox changes in the mid-Panthalassa Ocean remain debated. Here we present the results of geochemical and multivariate statistical analyses of a late Guadalupian to Lopingian (middle–late Permian) bedded chert succession from the Iwaidani section, Japan, which preserves pelagic deep-sea facies from the ocean floor to the lower flank of a mid-Panthalassan seamount. The entire section yields a low manganese-enrichment factor (MnEF <1), suggesting that suboxic conditions has appeared in the depositional environment already in the late Guadalupian. Enrichment factors of other redox-sensitive trace-elements (e.g., vanadium and uranium) and principle component analysis (PCA) of major element data show the development of suboxic to weakly anoxic conditions across the Guadalupian/Lopingian boundary. Subsequently, anoxic conditions, as inferred from enrichments in U, Mo, Ni, Cu, Zn, and Tl, were developed during the middle Lopingian. Extremely high concentrations of U and Mo (enrichment factors of ∼6 and ∼5,500, respectively) indicate that H2S-rich euxinic conditions developed during the latest Lopingian and around the time of the EPME. The cause of the shift toward more reducing conditions in the early–middle Lopingian is unknown, but PCA results suggest that the euxinic conditions occurred in association with intensified continental weathering in response to a temperature rise during the ca. 200 kyr before the EPME.
Highlights
The Permian/Triassic boundary (PTB) marks the most severe mass extinction of the Phanerozoic, characterized by the loss of ∼80% of marine invertebrate species (e.g., Erwin, 1994; Payne and Clapham, 2012; Stanley, 2016)
No correlations were found between these terrigenous elements and elements such as P, FIGURE 8 | CaEF, PEF, BaEF, middle REEs (MREE)/MREE*, Ce/Ce*, and PC3 score plotted with stratigraphy
Based on the geochemical interpretations of redox-sensitive elements and principal components from the Iwaidani section, we discuss the redox history of the Guadalupian–Lopingian deepsea Panthalassa, and compare our results with the PTB section at Gujo-Hachiman, where deep-sea oxic-dominated conditions have been proposed for the same period (Wignall et al, 2010; Fujisaki et al, 2019)
Summary
The Permian/Triassic boundary (PTB) marks the most severe mass extinction of the Phanerozoic, characterized by the loss of ∼80% of marine invertebrate species (e.g., Erwin, 1994; Payne and Clapham, 2012; Stanley, 2016). The contents of redox-sensitive trace-metals (e.g., U, Mo, and V) and quantitative analysis of framboidal pyrite size distribution from a PTB section at Gujo-Hachiman in Japan (Figure 1) show that the Lopingian deep-sea was dominated by oxic conditions, but that the oxygen minimum zone (OMZ) rapidly expanded at shallower depths in the mid-Panthalassa immediately before the EPME (Algeo et al, 2010, 2011b; Wignall et al, 2010; Fujisaki et al, 2019). Uranium isotopic studies of shallow-water carbonates from the Tethyan and Panthalassic oceans suggest that the global marine redox conditions during the Guadalupian and Lopingian (late Permian) were similar to those of the modern ocean, and that a major expansion of oceanic anoxia began ≤70 kyr before the EPME (Brennecka et al, 2011; Elrick et al, 2017; Zhang et al, 2018a; Zhang et al, 2020). The duration and intensity of the EPMErelated deep-sea anoxia remain debated
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