Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian–Triassic boundary: link to volcanism

Abstract

Mercury (Hg/TOC) spikes from eight Permian–Triassic boundary (PTB) sections in this study display patterns similar to each other across the so-called extinction interval as well as strong variation in sedimentation rates from section to section. Mercury may have been originated from the synchronous magmatism of the Siberian Traps Large Igneous Province (STLIP).

At the GSSP in Meishan, China, Hg/TOC peaks were observed in the latest Permian mass extinction interval (LPME) and Early Triassic mass extinctions (ETME). The successions at Hovea-3 (Australia), Ursula Creek (Canada), Idrijca (Slovenia), Rizvanuša (Croatia) exhibit Hg/TOC peaks at the LPME and PTB. The Rizvanuša section displays one peak at the ETME horizon, Zal and Abadeh (Iran) successions at the LPME and ETME horizons, while Misci/Seres (Tyrol/Italy) section shows an enrichment at the LPME. The largest Hg/TOC peaks at the LPME, PTB and ETME are, perhaps, linked to the beginning of stage 2 (extrusive hiatus) of the Siberian Traps LIP. The meaning of the Hg/TOC spike between the LPME event and the PTB in seven of these sections is fuzzy.

In the δ202Hg (MDF) vs Δ201Hg (MIF) cross plot, the majority of samples from the extinction interval appear within the volcanic-emission box and a few samples plot in the sediment/soil/peat box. Hg-isotope signatures resulted from mixing processes of volcanic and normal marine sediment Hg, generating four horizontal trends whose Δ201Hg shows negligible to no variation. Less terrigenous-Hg influx was noticed in the sections closer to the STLIP (Rizvanuša, Idrijca and Seres/Misci, all in Europe) in which Δ201Hg (MIF) is close to zero. Marked influence occurs in sections far distant from the STLIP (Meishan, Ursula Creek and Hovea-3) that exhibit negative Δ201Hg (MIF). The two sections from Iran, at intermediate distance from the STLIP, exhibit the highest, positive Δ201Hg values (Abadeh section) and the lowest, negative Δ201Hg values (Zal section). A Δ199Hg (MIF) vs Hg (n·ng−1) cross plot suggests that volcanic Hg has been contaminated by normal marine source-Hg influx in these sections helping to shape two major curved trends. The negative C-isotope excursions and Hg/TOC enrichments in the studied sections are nearly coeval and this supports the hypothesis of synchronism between the Permian–Triassic transition biotic crises (LPME and ETME) and the start of the stage 2 of the Siberian Traps (sill-intrusion style of magmatism).