UNDERSTANDING THE LATE ORDOVICIAN MASS EXTINCTION

The Late Ordovician mass extinction (LOME), which eliminated ~85% of marine species globally was the second most severe biotic crisis in the past 540 million years [1]. The LOME occurred in two pulses, one at the beginning of the Hirnantian stage, corresponding to the lower N. extraordinarius Zone and the other at the base of the N. persculptus Zone of the uppermost Hirnantian. Global cooling and habitat loss resulting from the waxing and waning of glaciers during the Hirnantian have been traditionally held to have caused the LOME [2]. However, the cycles of glaciation and associated sea level change during the Hirnantian likely were more complex than originally assumed. Oceanic anoxia has been linked to the LOME [3, 4], however, temporal changes in global redox conditions that could synchronise with each pulse of the LOME remains elusive. The emplacement of a large igneous province (LIP) also has been hypothesised as a driver for the LOME based on mercury (Hg) enrichments. However, the Hg enrichments in the sedimentary rocks of the Ordovician-Silurian boundary from South China have been argued to be sulphide-hosted rather than of volcanic origin, challenging the hypothesis of a volcanic driver for the LOME. In this presentation, I will present S-isotopic data in particular mass-independent S-isotopic signals [5] and other geochemical data from sedimentary successions from South China and elsewhere. I will discuss the stratospheric volcanic eruptions, ocean chemistry changes and their potential link to the LOME.

[1] Sheehan (2001) doi: 10.1146/annurev.earth.29.1.331

[2] Brenchley et al. (2003) doi: 10.1130/0016-7606(2003)115<0089:HRSISO>2.0.CO;2

[3] Zhang et al. (2009) doi: 10.1130/G25477A.1

[4] Hammarlund et al. (2012) doi: 10.1016/ j.epsl.2012.02.024.

[5] Hu et al. (2020) doi: 10.1038/s41467-020-16228-2