Regional investigation of extinction-recovery patterns during the Toarcian (Lower Jurassic) hyperthermal event

The Toarcian Stage of the Lower Jurassic marks a period of extreme environmental perturbations, including changes to the global carbon cycle, rapid warming to 'hyperthermal' conditions, and increased continental weathering and run-off.

These events have been linked to the eruption of the Karoo-Ferarr Large Igneous Province in the contemporary Southern hemisphere.

In many of the marine sedimentary basins in the Northern hemisphere the hyperthermal conditions led to stagnation, consequent sediment and water column de-oxygenation and the deposition of distinctive organic-rich laminated black shales (linked effects often termed the Toarcian Oceanic Anoxic Event - TOAE).

These challenging conditions caused an extinction event in the macrofauna (particularly the benthos) and in microfossil groups.

Recovery from this event was slow (several millions of years) and occurred only when environmental conditions improved after the TOAE.

The TOAE and associated pattern of extinction and recovery is well recorded in the Cleveland Basin of Yorkshire, and further afield in Germany and France. It has also recently been recognized globally, in, for example, Canada.

However, in many marine basins in Southern Europe laminated black shale facies are either weakly developed, or absent, yet there are still distinct patterns of biotic turnover during the Toarcian Stage as well as evidence for rapid and extreme warming.

This strongly indicates that while changes in marine oxygen levels during the Toarcian where regional in extent, warming was a global phenomenon and had a primary control on both environmental and biotic changes.

As such, the Toarcian Stage has lessons to teach us about the consequences of anthropogenic global warming now and in the future.