| Summary: | © 2018 Elsevier B.V. The sub-meridional seaway that connected Paleo-Arctic and Paleo-Tethys basins was one of the most important geographical attributes of the Late Paleozoic Pangean landscape, paleogeography and paleoclimate. Existing models about the timing of the disconnection of the Paleo-Arctic and the Paleo-Tethyan oceans is controversial and poorly documented. Warm-water benthic foraminifera (WWBF) were utilized to establish the precise timing of the closure of the Urals-Precaspian-Paleo-Tethys Seaway (UPTS) during Cisuralian time. The WWBF of Paleo-Tethys and those of the Ural—Precaspian Basins during the Gzhelian-Asselian, display a considerably high level of similarity. Beginning from the Sakmarian, the faunas of these two regions became dissimilar, suggesting a break in the connection between the Paleo-Tethys and Ural-Precaspian Basins. Sedimentological evidence (olistostromes and seismites) of the final collision of the Eastern Ural, Kazakhstania, Scythian-Turan plates with the southeastern part of the Russian Platform during Late Paleozoic also supports the emergence of the Precaspian Isthmus at the Asselian-Sakmarian transition. Oceanic currents in the Precaspian and the Southern Ural Basins before the Sakmarian were directed northward and later changed to the south. The biotic and sedimentologic features clearly suggest the UPTS closure and the origination of Precaspian Isthmus during the Asselian-Sakmarian transition. The abrupt changes in the oceanic circulation triggered changes in atmospheric CO2, atmospheric circulation and, possibly, albedo feedback. The emergence of the Precaspian Isthmus induced an increase in the poleward salt and heat transport towards mid- to lower latitude Gondwana and Cathasia margins. The warm water currents and moisture along the margins of Gondwana caused a rapid increase in the precipitation necessary to build significant ice sheets during the early-middle Sakmarian.
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