Late Cenozoic base-level variations of the Caspian Sea: A review of its history and proposed driving mechanisms

The Caspian Sea is characterized by significant variations in its base level during the late Cenozoic and provides an important repository for long-term records of both regional climate and tectonics due to its position within the interior of the Eurasian continent and at the northern margin of the ongoing Arabia–Eurasia collision zone. The Caspian also serves as an important moisture source for eastern Eurasia, including the northern Tibetan Plateau, and thus the history of Caspian base-level variations represents an important, and poorly understood constraint on paleoclimate reconstructions throughout Eurasia. Prior work in the Caspian region has largely focused on developing biostratigraphic age divisions and investigating the history of connection between the Caspian, Black, and Mediterranean seas, as well as the global ocean. Recent geochronologic work in the Caspian and related basins has questioned previous correlations of hydrologic events in these different basins. As a result, prior estimates of the chronology and magnitude of Caspian Sea level variations may be incorrect. Here we synthesize previous work to develop a new Caspian base level curve starting at the beginning of the Meotian regional stage (~7Ma). We also present a new synthesis of potential driving mechanisms for the large variations in Caspian base level and speculate on a possible cause for the enigmatic Akchagyl transgression. This synthesis highlights the dynamic range of Caspian Sea level, which varied from 200m above to in excess of 1000m below its current level during the Late Cenozoic, and provides a basis for future work investigating the tectonic and climatic drivers behind variations in Caspian base level. •A new synthesis of previous Caspian Sea base-level estimates from 7Ma to present.•A new review of potential driving mechanisms for Caspian base level.•Presents hypothesis for cause of previously enigmatic Akchagyl transgression.