The Siberian craton occupies the region between the Yenisey River on the west and the Lena River in the east. This region is known also as East Siberia. Total area is about 4,000,000 sq km. The central and southern parts of the craton constitute the Lena- Tunguska oil-gas province. The sedimentary section begins with Upper Proterozoic Riphean clastics and carbonates. Overlying these rocks discordantly is a section that consists of clastics, carbonates, and salt of Late Proterozoic Vendian, Cambrian, Ordovician, and Silurian age.
A series of elongate arch-like highs and linear anticlines extends along the southeast border of the Siberian craton. Their genetic nature is debated. The dimensions and morphology of these arches and anticlines are not typical of platform structures. They extend 500-600 km along the long axis and have amplitudes of 2000-2500 m. They are asymmetric with steep inner northwest flanks and gentle outer southeast flanks; axial planes are tilted toward the craton. These anticlines are thrust one upon the another. Anticlines predominate over synclines up to complete absence of the latter. Fronts of tectonic slices in the crystalline basement commonly correspond with the anticlines and arches.
Under reverberation folding is understood a complex of plicative-fault structures in the sedimentary cover of a craton that formed in part by the action of the frontal portion of overthrusting sheets of crystalline basement and in part by tangential pressure from allochthonous basement highs and processes involving salt. Four types of reverberation folding are recognized here.
The first of these, the tectono-type of which is the Zhilagov arch, was formed by tectonic activity of the crystalline basement - by frontal thrusting of a basement high.
The second kind (Shamanov high is the tectono-type) results from the action of tectonic slices that do not involve the entire sedimentary cover but only that part of the section below the salt. These are small highs 3-5 by 6-8 km. They coincide with frontal basement highs.
The third variety (Bozhekhan arch is the tectono-type) developed where a thrust passed into higher parts of a thrust sheet from displacement along the surface of the basement. Particularly interesting here is Pokrovka high in sediments of the Mota and Ushakov Formations.
The fourth type (Markovo arch is the tectono-type) has developed by horizontal displacement of the supra-salt complex along plastic salt. The section consists of three parts: sub-salt, salt, and supra-salt. The most deformed is the middle (salt) of the Lower Cambrian. It occurs in overturned anticlines. In the overlying Middle and Upper Cambrian are gentle arches. The Lower Cambrian and Vendian are practically horizontal.
Petroleum is expected to be found in these allochthonous structures.
(Taken largely from Sizykh, 1995; digested in Petroleum Geology, vol 31,
no. 2, p. 144-145.)
Copyright 2000, James Clarke. You are encouraged to print out this News
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My wife Lori joins me in wishing God's Blessing on all of you for a Joyous
Christmas and (continued next week!)...