Paleobiodiversity and paleoenvironments of the eastern Paratethys Pleistocene lacustrine-palustrine sequence in the Baklan Basin (SW Anatolia, Turkey)

The Lower-Upper Pleistocene sedimentary record of the Baklan Basin, a long-lived continental half-graben basin in SW Turkey, is characterized by shallow lacustrine and palustrine deposits. The paleoenvironmental changes recorded in the basin succession allow for a multiproxy approach in reconstructing the paleoclimatic, paleoecological, and paleobiogeographical evolution of southwestern Anatolia during the Early-Late Pleistocene. Based on sedimentological, paleontological, and geochemical data, three main types of depositional intervals have been identified, corresponding to different phases of a lake expansion cycle: The first interval is characterized by the perennial shallow lake environment (PSL deposits), which represents the very early stage of the Early Expansion System Tract (VEEST). This suggests a very early stage of lake transgression in arid climate conditions. The second interval is represented by the palustrine carbonate lake center environment (PLC deposits), which corresponds to the late stage of the Early Expansion System Tract (LEEST). This indicates a late early stage of lake transgression in semiarid to subhumid climates. The third interval is marked by the palustrine lake margin environment (PLM deposits), which represents the Late Expansion System Tract (LEST) under humid conditions. The Lower-Upper Pleistocene successions of the Baklan Basin provide an excellent example of lacustrine and palustrine deposition in a laterally extensive, low-gradient, shallow lake system in the semi-isolated Pontocaspian freshwater to slightly brackish water (oligohaline-low mesohaline) long-lived lake. The presence of Pontocaspian ostracod and mollusc faunas in the studied successions indicates that the largest major Caspian transgression around 2.6 millon years ago extended to SW Anatolia. The studied successions represent a rich archive of landscape, climate, and biotic development in the eastern Paratethys region during the Early-Late Pleistocene. The biogeographic signature of fossil faunas (mammals, ostracods, molluscs, and fishes) and floras (Characeae) is predominantly modern Palearctic and Holarctic, with a minor amount of endemic Pontocaspian elements. This study presents the Pleistocene Pontocaspian species of the Anatolian lakes that may have served as refugia for the Palearctic taxa during adverse time intervals. Consequently, this study shows that Lower-Upper Pleistocene lacustrine to palustrine sedimentation in the Baklan Basin has been controlled by the combination of tectonics, climate changes, and the largest major Caspian Sea transgression. The findings of this study could be used to evaluate the impact of similar allocyclic factors on the sedimentological, hydrological, and geochemical development of other intermontane lake basins.

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