Postglacial Deposits of the Dal’nyaya Taiga Group: Early Vendian in the Ura Uplift, Siberia. Communication 2. Ura and Kalancha Formations and History of the Basin

Аннотация

The paper presents the facies characteristics and sequence-stratigraphic reconstructions of the Lower Vendian postglacial deposits of the Dal’nyaya Taiga Group (Ura Uplift, Patom basin, Siberia). The section is divided into two sequences: the first sequence corresponds to the Barakun Formation; the second sequence, to the Ura and Kalancha formations. Together, they make up a continuous transgressive-regressive succession, with its significant part formed in a deep-water zone of the low-angle (about 1°) homoclinal carbonate–terrigenous and clayey–carbonate ramps. The upper sequence boundary passing along the top of deposits in the Kalancha carbonate platform corresponds to the stratigraphic hiatus at the Zhuya Group base. The fine-grained siliciclastic material, which makes up as much as 50 vol % of the Ura sediments, has an eolian origin. Probably, high activity of eolian processes promoted by a moderately cold arid or semiarid climate at that time was one of the reasons for high bioproductivity in the paleobasin. The consequent large-scale burial of organic matter could foster the reactivation of methanogenic processes. The lithological features of sediments were responsible for their thixotropic state that provoked the slumping of sedimentary masses during high seismic activity.