Depositional Environments of Prospective for Shale Gas Silurian Deposits of the East European Platform, Ukraine

The marine deep-water sediments of Silurian and Ordovician extend in south-eastern direction from the Polish border to Romania. Nature and intensity of the processes, which had an impact on the formation of the Silurian strata have been determined by the location of the region, which tectonically belonged to the zone of peri-cratonic subsidence, and paleooceanographically was the floor of the peri-continental sea. The continuous Silurian-Lower Devonian sequence shows almost sub-meridional strike of the clearly defined facial zones and significant increase of the thickness of stratones in western direction. Stratigraphically the Silurian sections made up of rather variable poly-facial sequences of the lagoon, shallow water, open shelf and slope sediments of the ancient basin. Their location and boundaries were changing with time and therefore the area of occurrence of similar facies at different stratigraphic levels do not coincide. The continental slope in paleo-basin was geomorphologically formed at the end of Ludlow, when the trough of the Teysseyre-Tornquist Zone rose and an intense subsidence started in it. At the beginning of Devonian the uplift movements at the platform caused the gradual shallowing and regression of the paleo basin, the eastern coastline of which in Pragian has moved to the TTZ.