Middle–Late Miocene Paleogeography of the Eastern Paratethys. Part VII. Regression of the Terminal Sarmatian: Paleogeography and Chronology of Events

The lost connection with open basins and the arid conditions of the second half of the Tortonian resulted in a negative water balance of the Late Sarmatian basin in its terminal stage and in a rapid drop of its level. The Sarmatian basin therewith broke up into several separate basins. Although the Caspian and Euxinian basins likely underwent intermittent disconnections during the Late Sarmatian, faunal similarities suggest the persistence of a unified and impoverished Khersonian ecosystem. The disconnection of the Dacian Basin and the West Kuban Trough probably occurred only at the very peak of the regression, about 8 Ma. After the separation, each of the residual basins had its own history, determined by their balance of runoff and evaporation. For the Dacian and West Kuban basins, through which all the river runoff from the outer Carpathians and the platform passed, a freshwater regime and discharge of excess water into the Euxinian basin are inferred. In the Dacian Basin, with moderately arid climate, the water level drop, according to seismic data, is estimated from ‒50 to ‒200 m; in the West Kuban depression, from ‒300 to ‒350 m; and in the Euxinian, from ‒450 to ‒500 m. The beginning of the Maeotian transgression, recognized from the appearance of marine Maeotian benthic fauna and diatoms in the Euxinian and Dacian basins, is dated as 7.65 Ma. The shallow-water sedimentation of coastal lagoon facies therewith still persisted in the areas of outer shelf of the preceding Middle‒Late Sarmatian sea.