Mercury evidence for combustion of organic-rich sediments during the end-Triassic crisis

Jun Shen,Henrik H Svensen,Runsheng Yin,Shane D Schoepfer,Thomas J Algeo

doi:10.1038/s41467-022-28891-8

Abstract

The sources of isotopically light carbon released during the end-Triassic mass extinction remain in debate. Here, we use mercury (Hg) concentrations and isotopes from a pelagic Triassic–Jurassic boundary section (Katsuyama, Japan) to track changes in Hg cycling. Because of its location in the central Panthalassa, far from terrigenous runoff, Hg enrichments at Katsuyama record atmospheric Hg deposition. These enrichments are characterized by negative mass independent fractionation (MIF) of odd Hg isotopes, providing evidence of their derivation from terrestrial organic-rich sediments (Δ199Hg < 0‰) rather than from deep-Earth volcanic gases (Δ199Hg ~ 0‰). Our data thus provide evidence that combustion of sedimentary organic matter by igneous intrusions and/or wildfires played a significant role in the environmental perturbations accompanying the event. This process has a modern analog in anthropogenic combustion of fossil fuels from crustal reservoirs.

Highlights

The sources of isotopically light carbon released during the end-Triassic mass extinction remain in debate
Global environmental and biotic perturbations, including extreme warming, ocean acidification and anoxia, and a mass extinction, characterize the Triassic–Jurassic (T–J) transition (~201 Ma)[1–4]. These consequences are believed to have been driven by rising atmospheric CO2 levels, which have been linked to the emplacement of the Central Atlantic Magmatic
The negative carbon isotope excursions (CIEs) of the T–J transition ranges in magnitude from

Summary

Introduction

The sources of isotopically light carbon released during the end-Triassic mass extinction remain in debate. Because of its location in the central Panthalassa, far from terrigenous runoff, Hg enrichments at Katsuyama record atmospheric Hg deposition These enrichments are characterized by negative mass independent fractionation (MIF) of odd Hg isotopes, providing evidence of their derivation from terrestrial organic-rich sediments (Δ199Hg < 0‰) rather than from deep-Earth volcanic gases (Δ199Hg ~ 0‰). The magnitude of the CO2 rise (~2–4×) during the T–J transition has been estimated by plant stomatal ratios as well as pedogenic carbonate isotopes[5,6], debate continues regarding the source(s) of excess CO2, with proposals of mantle-derived CO27, heating and devolatilization of organicrich and carbonate-bearing sedimentary rocks[8], and release of methane from permafrost or marine clathrates[9]. Volcanogenic emissions, the largest natural Hg source, supply Hg to the atmosphere with a residence time of 0.5–2 yr, playing a significant role in the global Hg cycle[13]

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