A volcanic trigger for the Late Ordovician mass extinction? Mercury data from south China and Laurentia

David S Jones,David A Fike,Anna M Martini,Kunio Kaiho

doi:10.1130/g38940.1

David S Jones, David A Fike + Show 2 more

Open Access

https://doi.org/10.1130/g38940.1

Copy DOI

Abstract

The Late Ordovician mass extinction (LOME), one of the five largest Phanerozoic biodiversity depletions, occurred in two pulses associated with the expansion and contraction of ice sheets on Gondwana during the Hirnantian Age. It is widely recognized that environmental disruptions associated with changing glacial conditions contributed to the extinctions, but neither the kill mechanisms nor the causes of glacial expansion are well understood. Here we report anomalously high Hg concentrations in marine strata from south China and Laurentia deposited immediately before, during, and after the Hirnantian glacial maximum that we interpret to reflect the emplacement of a large igneous province (LIP). An initial Hg enrichment occurs in the late Katian Age, while a second enrichment occurs immediately below the Katian-Hirnantian boundary, which marks the first pulse of extinction. Further Hg enrichment occurs in strata deposited during glacioeustatic sea-level fall and the glacial maximum. We propose that these Hg enrichments are products of multiple phases of LIP volcanism. While elevated Hg concentrations have been linked to LIP emplacement coincident with other Phanerozoic mass extinctions, the climate response during the LOME may have been unique owing to different climatic boundary conditions, including preexisting ice sheets. Our observations support a volcanic trigger for the LOME and further point to LIP volcanism as a primary driver of environmental changes that caused mass extinctions.

Highlights

Paleoclimate records indicate global cooling during ~35 m.y. of theEarly and Middle Ordovician, a relatively stable climate in the ~8-m.y.long Katian Age, and a glacial maximum in the Hirnantian Age (445.2– 443.8 Ma) (Trotter et al, 2008; Finnegan et al, 2011; Melchin et al, 2013)
The subsequent rapid expansion of Hirnantian ice sheets resulted in glacioeustatic sea-level fall and decreased temperatures (Finnegan et al, 2011) associated with the first pulse of the Late Ordovician mass extinction (LOME) (Melchin et al, 2013)
We document three Hg enrichments associated with the LOME and suggest that they are markers of large igneous province (LIP) volcanism

Summary

INTRODUCTION

And Middle Ordovician, a relatively stable climate in the ~8-m.y.long Katian Age, and a glacial maximum in the Hirnantian Age (445.2– 443.8 Ma) (Trotter et al, 2008; Finnegan et al, 2011; Melchin et al, 2013). The subsequent rapid expansion of Hirnantian ice sheets resulted in glacioeustatic sea-level fall and decreased temperatures (Finnegan et al, 2011) associated with the first pulse of the Late Ordovician mass extinction (LOME) (Melchin et al, 2013). Lefebvre et al (2010) used a coupled biogeochemical-energy balance model to demonstrate that chemical weathering of a hypothetical late Katian large igneous province (LIP) could have lowered CO2 over millions of years to cause major ice sheet growth. Phanerozoic mass extinctions have been linked geochronologically and mechanistically to the emplacement of LIPs

B Nevada

RESULTS

DISCUSSION

CONCLUSION