dominated emplacement to sill dominated emplacement, the latter of which would have liberated the largest amounts of trapped hydrocarbon deposits, coincides with the onset of the main phase of the mass extinction and is linked to a major negative excursion. A 2011 study led by Stephen E. Grasby reported evidence that volcanism caused massive coal beds to ignite, possibly releasing more than 3 trillion tons of carbon. The team found ash deposits in deep rock layers near what is now the Buchanan Lake Formation. According to their article, "coal ash dispersed by the explosive Siberian Trap eruption would be expected to have an associated release of toxic elements in impacted water bodies where fly ash slurries developed. ... Mafic megascale eruptions are long-lived events that would allow significant build-up of global ash clouds." In a statement, Grasby said, "In addition to these volcanoes causing fires through coal, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in earth history." A 2013 study led by Q.Y. Yang reported that the total amounts of important volatiles emitted from the Siberian Traps consisted of 8.5 × Tg CO, 4.4 × Tg CO, 7.0 × Tg HS, and 6.8 × Tg SO. The data support a popular notion that the end-Permian mass extinction on the Earth was caused by the emission of enormous amounts of volatiles from the Siberian Traps into the atmosphere. In addition, these volcanic eruptions released significant quantities of toxic mercury into the atmosphere and ocean, further contributing to large scale die-offs of terrestrial and marine life. A series of surges in mercury emissions raised environmental mercury concentrations to levels orders of magnitude above normal background levels and caused intervals of extreme environmental toxicity, each lasting for over a thousand years, in both terrestrial and marine ecosystems. Nickel aerosols released by volcanic activity further contributed to metal poisoning. Cobalt and arsenic emissions from the Siberian Traps caused further still environmental stress. Choiyoi Silicic Large Igneous Province A second flood basalt event that emplaced what is now known as the Choiyoi Silicic Large Igneous Province in southwestern Gondwana between around 286 Ma and 247 Ma has also been suggested as a possible extinction mechanism. Being about 1,300,000 cubic kilometres in volume and 1,680,000 square kilometres in area, this flood basalt event was approximately 40% the size of the Siberian