Литосфера (Feb 2018)
Sedimentology and stratigraphic correlation of Vendian deposits in the southwestern Siberian Craton: Major contribution of an exocratonic clastic source to sedimentary systems
Abstract
The study focuses on the sedimentation and stratigraphy of a large Vendian (Ediacaran) sedimentary basin in the southwestern Siberian craton, with implications for the origin of its units and subunits. Sediments are been correlated along the craton edge and inward into the craton interior using stratigraphic sequences, including glacial and post-glacial deposits. Clastic complexes in the Vendian: upper Chapa, Taseeva, Oselok, and Baikal groups composed of fluvial deposits are of special importance for correlations. The structure of the continental Aysa Fm. of the Oselok Group in the Sayany area has been characterized in detail, based on universal classification of lithofacies and their sequences, and correlated with sediments in the craton interior. There are two Ediacaran subunits: a continental-marine complex below and a continental complex above. The continental-marine subunit in the subsided craton margins was deposited mainly upon postglacial plains (sandurs) and marginal sea shelves, with contributions from intracratonic clastic sources. The deposits of the continental subunit belong to centripetal fluvial systems directed from distant craton-margin mountain upland toward the epicontinental sea in the central Siberian craton. The continental subunit is composed of large sections of red and variegated fluvial deposits from a foreland basin which was accumulated mainly in foredeeps in the over-compensation setting and partly reached the slopes of forebulges. Big deep sand rivers with large channel bars were formed at early and late during orogenic activity, while perennial anastomosing and braided mud-sand rivers with levees originate during passive stages of orogeny. The largest progradation of fluvial systems onto the Siberian craton is marked by channel deposits of the lower members from the Nemchanka, Moshakovka, Aysa, Khuzhir and Kachergat fms., as well as by the Bokhan sandstone member of the Chora Fm.
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