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The Siberian Traps - Lithostratigraphy

The lithostratigraphy of the Siberian Traps has been described in four main regions: Noril'sk, Putorana, Nizhnyaya-Tunguska, and Maymecha-Kotuy. Reviews are available in Fedorenko et al. (1996) and Sharma (1997).
The thickest part of the sequence (ca. 3500 m), at Noril'sk, is characterised by a wide variety of rocks types, including tuffs, picrites, basalts, and more evolved rocks such as basaltic andesite. The sequence is divided into 11 suites (or formations) on the basis of petrology and geochemistry, and these are grouped into two main sequences (Lower and Upper; the Upper sequence is volumetrically the more important).
At Putorana, where the sequence reaches 1800 meters in thickness, most of the rocks are homogeneous basaltic lavas, and have been correlated in the basis of their composition with part of the Upper Sequence at Noril'sk. The sequence at Nizhnyaya-Tunguska (up to 1000 meters thick) is dominated by basaltic tuffs, but the uppermost suites comprise basalt lavas.
Thick sequences of basalts and highly-alkaline rocks such as basanites occur in Maymecha-Kotuy, some 800 km to the northeast of Noril'sk. Unusual alkali picrites known as maymechites (pronounced 'meemesheets') occur in this region. Kamo et al. (2003) have confirmed that the Maymecha rocks were emplaced at the same time as the lavas at Noril'sk.
Reichow et al. (2002, 2005) have correlated the basalts from the West Siberian Basin with the low-Ti basalts of the Upper Sequence at Noril'sk, especially the Nadezhdinsky Suite. There is currently no correlation between the suites on the Siberian craton with those in Taimyr.
Figure Caption: Composite volcano-stratigraphic section of the Siberian Traps, modified after Sharma (1997), and based on Zolotukhin and Al'Mukhamedov (1988), Sharma (1981) and Fedorenko et al. (1996).

Magnetostratigraphy. The Ivakinsky suite at the base of the Noril'sk succession has reversed (R) polarity, whereas the younger suites are normally (N) magnetised (Lind et al., 1994; Campbell et al., 1992). However, Mitchell et al. (1994) have suggested that a small batch of samples from Nizhnaya-Tunguska have R polarity. This is despite them being correlated (on the basis of composition) with the N polarity Upper Sequence at Noril'sk. Either the geochemical correlation is incorrect, or there is at least one interval of reversed polarity that is not preserved within the Noril'sk succession. Samples from Maymecha-Kotuy have N-R polarity, and the successions found in deep drill SG-6 are N-R-N-R-N (Westphal et al., 1998; Gurevitch et al., 2003). These data suggest that the magmatism occurred over a longer time span than indicated by the radiometric dating.