The Ozerninskaya Strata of the Uda-Vitim Zone (Western Transbaikalia, Russia): Composition, Age, and Formation Environment

The results of the lithological and biostratigraphic study of the Ozerninskaya strata, the accumulation of which is associated with the beginning of the early Hercynian stage in the development of the Uda-Vitim structural-formational zone of the Baikal-Vitim folded system and the formation of gold-pyrite-polymetallic ore deposits of the Ozerninsky ore cluster, are considered. The strata is isolated from the Lower Cambrian Oldynda Formation. It is composed predominantly of greywacke arkose and quartz greywacke and includes two substrata. The lower substrata is represented by quartz-feldspar sandstone and siltstone with interlayers and lenses of polymictic conglomerate and gritstone, while the upper substrata is composed of interbedded polymictic sandstone and siltstone, calcareous siltstone and limestone with interlayers of clayey, clayey-siliceous, coal-clayey siltstone and mudstone. The paleontological characteristics of the Ozerninskaya strata determines its stratigraphic belonging to the Lower (Emsian Stage) - Upper (Lower Frasnian Substage) Devonian. The composition, structure, and paleo-biota indicate that the sediments formed in the open shelf sea environment with a significant input of terrigenous component. The lower substrata deposited in the shelf shallow water conditions, with active hydrodynamics, while the upper substrata accumulated in the most submerged parts of the shelf, in areas with stagnant hydrogeological regime.