Prehistoric mega-lake sediment offers key insight into how inland regions responded to ‘super-greenhouse’ event

A pioneering new study, carried out by a team of British-based researchers, has analysed sediments from the site of the vast lake which formed in the Sichuan Basin, in China, around 183 million years ago in the Jurassic period.

The study showed that an accelerated hydrological cycle operating in this region at the time brought an increased supply of nutrients to the lake, which in turn encouraged biological productivity. As a result, the team were able to find an abundance of dark-coloured, organic-rich sediments deposited in the area.

These organic-rich sediments are similar to those found deposited in many of the world's oceans at the same time, suggesting that both systems drew vast quantities of carbon dioxide from the atmosphere, consequently aiding global recovery from climate change, but at the same time losing the dissolved oxygen crucial to larger aquatic organisms.

The research is published in the scientific journal Nature Geoscience.

Professor Stephen Hesselbo, a Professor of Geology at the University of Exeter's Penryn Campus, in Cornwall and co-author of the research, explained: "This research is exciting because for the first time we can connect the profound environmental changes that took place in Jurassic oceans to changes of similar magnitude in lakes and track the resultant carbon burial."

Until now, the vast majority of research on these so-called 'super-greenhouse events' has been conducted on material deposited in marine environments.

However, this latest study examined sediments from the vast former lake in China -- more than twice the size of England and almost four times the size of Lake Superior -- which formed when warming atmospheric temperatures, due to the massive release of greenhouse gases such as carbon dioxide and methane, led to increased rainfall in continental interiors and high nutrient levels in lakes as well as oceans. Ironically, the oxygen-depleted conditions that ensued led to deposition of black shales, exactly the rock type now exploited as a source of oil and gas.

Professor Hesselbo added: "What the team has managed to do here is to apply a whole range of quite sophisticated dating techniques that demonstrate synchrony of major environmental changes across the globe at the time -- highlighting the very great extremes to which the planet's climate can be pushed from massive carbon emissions, albeit naturally caused in this case."