Siberian Traps - Geological Setting

The main surface outcrop of the volcanic rocks (predominantly basaltic lavas and tuffs) are found on the Siberian Craton (east and south of the thick-dashed line on the map, right), and on the Taimyr Peninsula. However, extensive subcrops of basalt also occur beneath the West Siberian Basin (or Siberian Platform) (Surkov, 2002), beneath the Yenesei-Khatanga Trough, and beneath the Kara Sea; the total area (and volume) of these 'hidden' basalts may exceed those of the main outcrops to the east. Sporadic outcrops of Permo-Triassic basalt occur in the Urals and in the Kuznetsk Basin, and our recent dating studies have shown that many of these are contemporaneous with the Permo-Triassic boundary (Reichow et al., 2009)

Intrusive rocks occur throughout the region, especially on the Siberian Craton around the main outcrops of lavas, and basaltic pyroclastic rocks are abundant in the lower parts of the volcanic succession (Fedorenko et al., 1996; Sharma, 1997; Ross et al., 2005).

On the craton, the basalts erupted onto, or intruded into, Palaeozoic sedimentary sequences, including the coal-bearing Permo-Carboniferous Tunguska sequences. In the West Siberian Basin, the basalts lie on top of Palaeozoic or Proterozoic basement, although the precise nature of this contact is poorly constrained from borehole and seismic data.

Figure Caption. Map of western Siberia showing the extent of the Siberian Traps (lavas, tuffs and intrusives, green) on the Siberian Craton, and the postulated subcrop extent of Permo-Triassic basalts beneath the West Siberian Basin (red). Also shown are some of the commericial boreholes in the West Siberian Basin, many of which have yielded basaltic rocks, and the main N-S rift systems, the Urengoy (Ur) and Khodosey (Kh) Rifts. Outcrops of Permo-Triassic basalt are found in Taimyr, the Ural Mountains, Central Asian Foldbelt, and Kutznetsk Basin (or Kuzbass). Map modified from Reichow et al. (2009) and Saunders and Reichow (2009).

The Siberian Craton is old, cold and thick, unlike the much younger lithosphere of the WSB, which is young, thin and hot. Furthermore, whereas the Craton has remained stable since the Permian (and probably for a long time before that), the Palaeozoic surface of the West Siberian Basin has subsided. Not only has this resulted in deep burial of the basaltic sequences, but it has helped create substantial oil and gas fields - some of the world's largest (Peterson and Clarke, 1991).

Deep, north-south trending rifts occur within the WSB. These are termed the Urengoy (central WSB) and Khodosey (eastern WSB) rifts. Now buried beneath several kilometres of sediment, these structures contain thick sequences of Permo-Triassic basalt (see review by Saunders et al., 2005). The relative timing between rifting and volcanism remains unconstrained.