Seminar: Using sedimentary geochemistry to unravel episodes of major climate change

Using sedimentary geochemistry to unravel episodes of major climate change

Lawrence Percival (University of Lausanne, Switzerland)

The last 500 million years of Earth’s history have been punctuated by numerous episodes of abrupt climate change and mass extinctions, the best known (though not largest) of which was the extinction of the dinosaurs 66 million years ago. Whilst this event has been famously and compellingly suggested to have been caused by an asteroid impact, many of the other climate/extinction events record little or no evidence for such impacts, and have instead associated with large scale volcanic activity during the emplacement of Large Igneous Provinces (LIPs). LIP volcanism represents the geologically abrupt emplacement of millions of cubic kilometres of (chiefly) basaltic magma, and the ages of basalts from many LIPs are broadly the same as established dates of extinction/climate change episodes.

However, precisely matching the timing of LIP volcanism with the onset of climate change and extinctions, and establishing a mechanism linking these phenomena, remains a challenge. In this talk I will present geochemical data from numerous sedimentary records of two Mesozoic events: the end-Triassic mass extinction (201.5 Ma) and the Toarcian Oceanic Anoxic Event (~183 Ma). Carbon-isotopes can be used to trace major perturbations to the global carbon cycle (such as input of isotopically light methane/CO2, or the large-scale burial of organic matter). Osmium isotopes can be used to track increases in volcanic activity and/or continental weathering rates. Mercury concentrations can be used as another proxy of volcanism. Therefore, by combining these proxies in sedimentary records of these two events, it is possible to show how multiple surface processes on Planet Earth were operating and interacting during times of major environmental perturbation.