Siberian Traps

Geographical extent

Vast volumes of basaltic lava covered a large expanse of Siberia in a flood basalt event. Today the area covered is about 2 million square kilometres (770,000 square miles)—roughly equal to western Europe in land area—and estimates of the original coverage are as high as 7 million square kilometres (2,700,000 sq mi). The original volume of lava is estimated to range from 1 to 4 million cubic kilometres (240,000–960,000 cu mi).

The area covered lies between latitude 50° and 75° north and longitude 60° to 120° east.

Formation

The source of the Siberian Traps basalt has variously been attributed to a mantle plume (e.g. the Iceland plume) which impacted the base of the earth's crust and erupted through the Siberian Craton, or to processes related to plate tectonics. Another possible cause may be the impact that formed the Wilkes Land crater, which may have been contemporaneous and would have been nearly antipodal to the Traps. This controversial scientific debate is ongoing.

The Siberian Traps are considered to have erupted via numerous vents over a period of roughly a million years or more, probably east and south of Norilsk in Siberia. Individual eruptions of basalt lavas could have exceeded 2000 km³.

The presence of extensive tuff and pyroclastic deposits suggests that a number of large explosive eruptions occurred during or before the eruptions of basaltic lavas. The presence of silicic volcanic rocks such as rhyolite is also indicative of explosive eruptions.

Impact on prehistoric life

This massive eruptive event spanned the Permian-Triassic boundary, about 250 million years ago, and is cited as a possible cause of the Permian-Triassic extinction event. One of the major questions is whether the Siberian Traps were directly responsible, or if they were themselves caused by some other, larger event, such as an asteroid impact. A recent hypothesis put forward is that the volcanism was a trigger that led to an explosion of the growth of Methanosarcina, a microbe that then spewed enormous amounts of methane into Earth's atmosphere.

This extinction event, also called the Great Dying, affected all life on Earth, and is estimated to have killed about 90% of all species living at the time. Life on land took at least 30 million years to fully recover from the environmental disruptions which may have been caused by the eruption of the Siberian Traps. Calculations of sea water temperature from δ¹⁸O measurements indicate that at its peak, the earth underwent lethally hot global warming, in which equatorial ocean temperatures exceeded 40 °C (104 °F).

Paleontological evidence further indicates that the global distribution of tetrapods vanished, with very rare exceptions in the region of Pangaea that is today Utah, between latitudes bounded by approximately 40°S to 30°N. The tetrapod gap of equatorial Pangea coincides with an end-Permian to Middle Triassic global "coal gap" that indicates the loss of peat swamps. Peat formation, a product of high plant productivity, was reestablished only in the Anisian stage of the Triassic, and even then only in high southern latitudes, although gymnosperm forests appeared earlier (in the Early Spathian), but again only in northern and southern higher latitudes. In equatorial Pangea, the establishment of conifer-dominated forests was not until the end of the Spathian, and the first coals at these latitudes did not appear until the Carnian, ~15 million years after their end-Permian disappearance. These signals suggest equatorial temperatures exceeded their thermal tolerance for many marine vertebrates at least during two thermal maxima, whereas terrestrial equatorial temperatures were sufficiently severe to suppress plant and animal abundance during most of the Early Triassic.

Nickel deposits

The giant Norilsk-Talnakh nickel–copper–palladium deposit formed within the magma conduits in the main part of the Siberian Traps.