Home – Home – Jornals – Russian Geology and Geophysics 2012 number 9

The problem of the Late Meso-Cenozoic tectonics and geodynamics of the southern framing of the Siberian Platform is discussed. This area abounds in Late Meso-Cenozoic structures composed of sedimentary deposits. Analysis of voluminous geologo-stratigraphic, geophysical, and geochronological (track dating) data showed that these structures, including the Baikal Rift Zone, resulted fr om the far-range impact of two collisions related to the prolonged convergence of the North China and Indian continents with Eurasia, which took place in the Late Jurassic-Paleocene and Cenozoic, respectively. The synchronous occurrence of two great tectonic events led to the formation of a complex structure and a sedimentary basin, which are of different geodynamic nature and cannot be united into the same sequence of Late Cretaceous-Cenozoic formation of the Baikal Rift Zone.
The Baikal system of shears and conjugate rifts formed in the Pliocene-Quaternary as a result of the far-range impact of the Indo-Eurasian collision. The latter led to the accumulation of the upper layered undeformed seismostratigraphic complex in all three Baikal basins. The sediments in Central Baikal are up to 3 km thick, and in the Selenga River valley they reach 5-6 km in thickness. The active intracontinental rift structures are characterized by zonal sedimentation. The middle layered deformed seismostratigraphic complex 1-1.5 km thick is recognized in all three Baikal basins and is similar to the Upper Oligocene-Lower Pliocene sediments of lacustrine-littoral, deltaic, and lacustrine facies widespread throughout the Baikal and Altai-Sayan regions and in Mongolia, wh ere they formed in the environments of large lake systems. As a result of the deformations caused by the Indo-Eurasian collision, the Upper Oligocene-Lower Pliocene sediments were involved in the Pliocene-Quaternary ramp and inilateral-ramp structures in intermontane basins of the Altai-Sayan region and in Mongolia. The lower seismically transparent seismostratigraphic complex occurs only in South Baikal and Central Baikal. It is 1 km thick in the east and up to 4-5 km thick in the west. The complex is a fragment of the Late Cretaceous-Paleogene lacustrine-river sediments of the large fore-Baikal piedmont basin, which formed at the final stage of evolution of the vast Mongolo-Okhotsk orogen.