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Julius Sovetov, Trofimuk Institute of Petroleum Geology and Geophysics Siberian Branch RAS (Russian Federation)
Sergei Moiseev, Trofimuk Institute of Petroleum Geology and Geophysics of Siberian Branch RAS (Russian Federation)
Vladislav Blagovidov, Novosibirsk State University (Russian Federation)
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The peripheral foreland basin extending in the south-west of Siberian Craton over 3000 km has been formed in the time of Cadomian (Baikalian) Orogeny. The external side the foreland basin was restricted by mountains to which the alluvial plains were joined. The Nepa-Botuoba and Baikit forebulges (anteclises) have separated the foreland basin from intracratonic carbonate platform that extended to north and north-east Siberian Craton boundaries and passed to remnant basin in Patom Upland. In the foredeeps the Late Ediacaran deposits thickness attained 1,5-2 km and in Nepa-Botuoba and Baikit forebulges their stratigraphic analogues are from zero to 100 m. The forebulges about 350 km width extend subparallel to foredeeps and on the scale and active stages may be identify as lithospheral folds.
The forebulges have north-west and north-east strike and the Siberian Craton hence has been pressed at two sides in the initial phase of Gondwanaland assembly. Sindepostional origin of the forebulges is emphasized by disconformities correlated to orogenic stages. The Pre-Katanga regional unconformity related to finish stage of the Siberian Craton compression at the Ediacaran-Cambrian boundary. Preconditions for different facies correlation two facts were used:
(1) the centripetal currents and distribution of clastics in Early Ediacaran and centrifugal these in Late Ediacaran, and consequently (2) sea transgressions direct from south-western marginal seas and carbonate deposits pinch-out to craton in Early Ediacaran and this from northern passive margin to south-western foredeeps in Late Ediacaran.Two main belts of sedimentation were established: (1) foredeeps with fluvial and fluvial-deltaic systems (molasse), (2) forebulges and their slopes with carbonate and terrigene-carbonate bar systems and stromatolitic buildups. In foredeeps the molasse composed of red colour, grey and black clastic deposits of Nemchana Fm., Greben Fm., Aisa Fm., Khuzhir Fm., and Kachergat Fm., and their stratigraphic analogue the phytolithic dolomite with anhydrite nodules make up the Oskoba Fm. and Tira Fm. External correlation chart include a few markers: (1) tillite of Marinoan epoch, (2) postglacial cap-dolostone, (3) high effective sandy fluvial systems related to orogeny onset and finish, (4) incision of river valleys at end of Ediacaran and following regional sea transgression at the time of orogen collapse. Collision and mountains raising manifested in foredeeps as fluvial systems with deep channels which replaced by anastomosing river systems with abundant levee and flood deposits in passive periods. The first stage marked by large flux of sand into basin and formation of regional sandy Bokhan Member.
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