The legacy of the Tethys Ocean: Anoxic seas, evaporitic basins, and megalakes in the Cenozoic of Central Europe

Abstract

At the end of the Eocene, the demise of the Tethys Ocean led to the formation of one of the largest anoxic seas in the last 50 million years of Earth history. This long-lived anoxic water body, named Paratethys, covered large parts of central Eurasia and functioned as a major carbon sink for 15-20 million years, characterised by the deposition of cherts, anoxic turbidites and black shales. The anoxic episode was followed by a phase of instable connectivity where full marine episodes alternated with evaporitic crises and lacustrine episodes, resulting in the deposition of marine molasses, evaporites and continental-lacustrine sediments. Finally, Paratethys transformed into a megalake that progressively filled with clastic sediments from the neighbouring mountain ranges. Paratethys was tectonically fragmented in numerous sub-basins that spread W-E from the Alpine and Carpathian orogens to the East European Platform. Most Paratethyan stratigraphic records from Central and Eastern European tectonically-active regions are not complete and thus hamper paleogeographic and paleoenvironmental reconstructions. The only exception is the Outer Carpathian Basin, located in the external part of the Carpathian arc in Central Europe, that preserved a complete record of Tethys demise and the rise and fall of Paratethys. The Outer Carpathians sedimentary successions show various lithologies that reflect an interplay of interbasinal connectivity and water exchange with the global ocean. Here we review the stratigraphic schemes of the different tectonic domains of the Outer Carpathians and describe the most complete records to produce a Carpathian-wide framework for the Eocene to Miocene evolution of Paratethys, the lost sea of Eurasia. Finally, we focus on the paleogeographic reconstructions of the interbasinal Paratethys connections and discuss how marine connectivity influenced anoxia and hypersalinity and impacted the Cenozoic depositional environments in central Europe.