Geological Backgrounds Of Siberian Traps

 Geological Backgrounds Of Siberian Traps

The Siberian Carton is old, cold and thick, unlike the much younger lithosphere of the WSB, which is young, thin and hot. Furthermore, whereas the Carton has remained stable since the Permian (and probably for a long time before that), the Paleozoic 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).

Map of western Siberia showing the extent of the Siberian Traps (lavas, tuffs and intrusives, green) on the Siberian Carton, ins, Central Asian Fold belt, and Kutznetsk Basin (or Kuzbass).

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 kilometers of sediment, these structures contain thick sequences of Perm o-Triassic basalt . The relative timing between rifting and volcanism remains unconstrained. 

The main surface outcrop of the volcanic rocks (predominantly basaltic lavas and tuffs) are found on the Siberian Carton (east and south of the thick-dashed line on the map, right), and on the Taimyr Peninsula. However, extensive sub crops 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 Perm o-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 Perm o-Triassic boundary (Reichow et al., 2009)

Intrusive rocks occur throughout the region, especially on the Siberian Carton 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 carton, the basalts erupted onto, or intruded into, Paleozoic sedimentary sequences, including the coal-bearing Perm o-Carboniferous Tunguska sequences. In the West Siberian Basin, the basalts lie on top of Paleozoic or Proterozoic basement, although the precise nature of this contact is poorly constrained from borehole and seismic data.