Paleoenvironmental evolution of the Eastern Paratethys: Tracing the Tethys Ocean legacy through geochemical proxies

Abstract

During the Oligocene to Miocene, the Paratethys Sea emerged as the northern offshoot of the Tethys Ocean, separated from the Mediterranean by the Alpine-Himalayan mountain range. Its history was characterized by the opening, restriction and closure of marine gateways, resulting in significant paleoenvironmental changes, including episodes of anoxia and extreme salinity fluctuations. This study investigates the paleoenvironmental evolution of the Paratethys Sea by focusing on variations in salinity and paleoventilation through advanced geochemical analyses of key sections (Belaya, Panagia, Zhelezhny Rog) in the northern Caucasus and Taman Peninsula of Russia, spanning 42 to 4 Ma. We apply a suite of geochemical proxies to reconstruct paleosalinity [e.g., using the boron/gallium (B/Ga), strontium/barium (Sr/Ba), sulfur/total organic carbon (S/TOC) ratios] and paleoredox conditions [e.g., using the organic carbon/phosphorus (Corg/P) ratio as well as trace-metal enrichment factors such as ZnEF, VEF, and MoEF]. Our results indicate that Paratethys was influenced by both global and local events, with regional factors becoming increasingly significant as isolation and fragmentation progressed. Paleoventilation proxies reveal two main episodes of anoxia: the Kuma Anoxic Event, a regional event exhibiting oceanic anoxic signatures that encompassed the time of the Middle Eocene Climatic Optimum (MECO) and; the Maikop Persistent Basin Water Stratification (PBWS) event, coinciding with the Eocene-Oligocene Transition (EOT) and lasting until the Middle Miocene Climatic Optimum (MMCO), reflecting characteristics of an enclosed sea; and a weaker, less stable suboxic-anoxic episode in the late Miocene, associated with Megalake Paratethys. Paleosalinity proxies depict both transitions from marine to brackish conditions, such as the late Maikop salinity decrease and significant short-lived marine episodes, such as the MMCO-related mid-Langhian flood (14.8 Ma), the Badenian-Sarmatian Extinction Event (12.65 Ma) and the Intra-Maeotian Event (6.8 Ma). These findings emphasize the critical role of marine connectivity as a trigger of salinity and ventilation changes in the Eastern Paratethys's evolution, laying the groundwork for future studies on restricted basins.