Hydrological changes in restricted basins: Insights from strontium isotopes on Late Miocene-Pliocene connectivity of the Eastern Paratethys (Dacian Basin, Romania)

The Dacian Basin was uniquely situated to record late Miocene hydrological changes that influenced depositional environments and faunal dispersal patterns in Central Eurasia’s mega-lake Paratethys. Differences between the high strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) of the waters from Lake Pannon and local Carpathian rivers and low ⁸⁷Sr/⁸⁶Sr of the Eastern Paratethys (Black Sea ‒ Caspian Sea) allow a thorough investigation of connectivity and water fluxes in the transient Dacian Basin. We present a detailed ⁸⁷Sr/⁸⁶Sr record for the Dacian Basin, which provides an exceptional record of basin connectivity from the latest Tortonian (ca. 7.7 Ma) until the early Pleistocene (ca. 1.8 Ma). Data show that a late Tortonian transgression (7.6–7.4 Ma) started with an incursion of Eastern Paratethys waters into the Dacian Basin, after which local rivers became the dominant source for the mostly freshwater environments of the early Messinian. The regional Maeotian-Pontian transitional interval (6.3–5.9 Ma) records a second incursion of Eastern Paratethys waters, but this time with an additional marine (Mediterranean) influx coinciding with a short-lived salinity incursion. During the Messinian Salinity Crisis of the Mediterranean, the Dacian Basin progressively connected with the Eastern Paratethys (5.9–5.5 Ma), after which it became restricted during the peak Mediterranean lowstand (5.5 Ma) and filled with Lake Pannon and local river water (5.5–5.3 Ma). During the Plio-Pleistocene, the Dacian Basin reconnected with the, at that time isolated, Black Sea, which shows similar ⁸⁷Sr/⁸⁶Sr as in the Last Glacial Maximum.