Middle–Late Miocene Paleogeography of the Eastern Paratethys. Part I. Introduction. Tectonic Structure of the Basins. Seismostratigraphic Analysis

The history of the evolution and disintegration of the giant inland sea of the Eastern Paratethys is described and illustrated in seven paleogeographic maps for relatively short time intervals from the end of the anoxic regime in the Tarkhanian time 14.9 Ma, to the catastrophic regression in the terminal Sarmatian 7.9 Ma, when the sea level dropped by 450–500 m. The Paratethys emerged in the Late Eocene–Early Oligocene at the rear of the Tethys Ocean closure front and consisted of two large basins: the Carpathian (Central Paratethys) and the Euxine-Caspian (Eastern Paratethys). In the south, the Neogene basins were limited by the Dinorides, Pontian structures, and the Lesser Caucasus and Elburz orogens. Of these basins, the West and East Black Sea and South Caspian basins were the deepest. At the end of the Middle Miocene–Late Miocene, the Eastern Paratethys also included the Dacian Basin. The transgressive-regressive history of the Eastern Paratethys and the evolution of its inhabitants followed its varying connections with open basins: when they expanded, the World Ocean level was established in the Eastern Paratethys, and it was populated by Mediterranean marine organisms. When the straits closed, the Paratethys became a vast isolated or semi-isolated sea-lake, with the water level and salinity depending on the ratio of river runoff and evaporation, and a highly endemic biota was quickly formed in the basin. The tectonic structures that were active during the Neogene and influenced the history of the Paratethys evolution are discussed. Based on seismostratigraphic analysis of regional profiles, the regional structure of sedimentary strata for various facies zones of the Eastern Paratethys was studied. The main indicators of a water level drop and erosion base-level changes are identified. The shallowest shelf areas contain extended parallel horizons, while the deeper parts of the shelves and troughs are characterized by clinoforms. Sections of deep basins show parallel reflections complicated by landslides and alluvial fans near the slopes. In almost all zones, the section is disrupted by erosional unconformable boundaries formed during regressions. Their greatest number is observed on the northern shelf, where sea level fluctuations are most distinctly manifested. Only the largest middle and terminal Sarmatian regressions are identified in the troughs and on the slopes. Complete Miocene successions with conformable boundaries are known in the central parts of the deep basins.