Sills and gas generation in the Siberian Traps

Abstract

On its way to the surface, the Siberian Traps magma created a complex sub-volcanic plumbing system. This resulted in a large-scale sill emplacement within the Tunguska Basin and subsequent release of sediment-derived volatiles during contact metamorphism. The distribution of sills and the released sediment-stored gas volume is, however, poorly constrained. In this paper, results from a study of nearly 300 deep boreholes intersecting sills are presented. The results show that sills with thicknesses above 100 m are abundant throughout the upper part of the sedimentary succession. A high proportion of the sills was emplaced within the Cambrian evaporites with average thicknesses in the 115-130 m range and a maximum thickness of 428 m. Thermal modelling of the cooling of the sills shows that the contact metamorphic aureoles are capable of generating 52-80 tonnes of CO m with contributions from both marine and terrestrial carbon. When up-scaling these borehole results, an area of 12-19 000 km is required to generate 1000 Gt CO This represents only 0.7-1.2% of the total area in the Tunguska Basin affected by sills, emphasizing the importance of metamorphic gas generation in the Siberian Traps. These results strengthen the hypothesis of a sub-volcanic trigger and driver for the environmental perturbations during the End-Permian crisis.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

New constraints on the age, geochemistry, and environmental impact of High Arctic Large Igneous Province magmatism: Tracing the extension of the Alpha Ridge onto Ellesmere Island, Canada

“…However, it has been argued that the release and distribution of magmatic volatiles is greatly reduced in submarine environments compared to subaerial eruptions (e.g., Percival et al, 2018). Furthermore, a submarine LIP erupting through ocean crust would not generate the additional volatiles compared to a LIP erupting through a sedimen-tary basin, through thermal metamorphism of sediments (e.g., CO 2 , CH 4 , CH 3 Cl, CH 3 Br, CO 2 , and Hg) (Svensen et al, 2018a;2018b;Grasby et al, 2019).…”

Placing our current ‘hyperthermal’ in the context of rapid climate change in our geological past

“…Many of these LIPs are not only associated with vast outpourings of volcanic rock at the surface, but they are also frequently associated with magma intruding into sedimentary rocks in the subsurface. Gases such as CO 2 and SO 2 are released directly from the surface volcanism, but as Svenson et al [70] discuss, the sedimentary rocks intruded by sills and dykes undergo significant metamorphism, releasing vast quantities of a variety of other gases (CO 2 , CH 4 , CH 3 Cl and CH 3 Br). Importantly, the emplacement of such intrusives is geologically fast and can dominate the greenhouse gas budget; indeed, just approximately 1% of the total area of the Tunguska Basin affected by sill intrusion could generate 1000 Gt CO 2 (272 Pg C [70]).…”

“…Gases such as CO 2 and SO 2 are released directly from the surface volcanism, but as Svenson et al [70] discuss, the sedimentary rocks intruded by sills and dykes undergo significant metamorphism, releasing vast quantities of a variety of other gases (CO 2 , CH 4 , CH 3 Cl and CH 3 Br). Importantly, the emplacement of such intrusives is geologically fast and can dominate the greenhouse gas budget; indeed, just approximately 1% of the total area of the Tunguska Basin affected by sill intrusion could generate 1000 Gt CO 2 (272 Pg C [70]). The recent high-precision dating of the sill emplacement in Siberia and its coincidence with the negative carbon isotope excursion at the P-T extinction event [39] strengthens this link.…”

Field evidence for coal combustion links the 252 Ma Siberian Traps with global carbon disruption

“…Siberian Traps magmas were chambered within, and intruded through, the Tunguska sedimentary sequence (Il'yukhina and Verbitskaya, 1976). The Tunguska Basin varies between 3 and 12 km thick, and includes carbonates, evaporites, oil and gas, and coal (e.g., Svensen et al, 2018). Coal strata range in age from Carboniferous to Permian, with a cumulative coal thickness of ∼100 m (Ryabov et al, 2014).…”