Late Miocene Euphrates River drained into a partially desiccated eastern Mediterranean

Abstract Although the Euphrates River—stretching ~3,000 km across Western Asia—has shaped the region’s geology for millions of years, the timing of its origin and the evolution of its course remain enigmatic. So far, two contrasting hypotheses have been proposed to explain the fluvial system’s Late Neogene path: termination in Anatolia at a palaeo-lake or the Mediterranean, or a southeastward continuation to Arabia. Here we use seismic-reflection and topographic data to show that two previously identified sedimentary accumulations—deposited during the terminal phase of the Late Miocene Messinian salinity crisis—resulted from dual riverine systems that drained into a partially desiccated eastern Mediterranean before avulsing toward the Persian Gulf and converging to form the modern Euphrates River. From probabilistic sediment-budget modelling, we show that although the latest Messinian drainage basins were an order of magnitude smaller than their present-day extents, the total palaeo-discharge exceeded that of the modern Tigris, Euphrates and Nile rivers combined, indicating intense palaeo-precipitation and high palaeo-relief. These results suggest that plate-margin deformation both controlled the fluvial avulsions that diverted the Euphrates River from the Anatolian–Eurasian Plate to the Arabian Plate, and established the conditions necessary for the development of the alluvial Fertile Crescent.