Lake level changes and paleo-precipitation estimations based on colluvial stratigraphy of Holocene sediments in West Anatolia (Simav Graben)

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Ocakoğlu F.



Time-controlled quantitative climate data are crucial for reconstructing past environmental contexts of human history. In west Anatolia, the Simav Graben used to be occupied by a lake. However, today it is drained and associated with Holocene sediments that record lake level changes. An initial drill-core at the lake's centre reveals an arid phase before ca. 14 ka (i.e. prior to the Late Glacial warming) followed by a wet phase (marshes and lake) throughout the Holocene. Along the lake's margin, two additional sediment sequences contain a detailed Holocene record of changes in humidity throughout the Simav Graben's watershed. Classification of the shoreline facies from these sequences records drought events marked by colluvium prograding towards the lake. Using 13 radiocarbon dates, sedimentary facies suggest rapid lake contraction phases grossly around 8.0, 3.9, 2.9, 2.4 and 2.0 ka. After the drier periods, recorded by phases of terrestrial progradation, lake level increase is marked by retrogradational lake muds and peats onlapping the colluvium, consistent with increases in total lake volume. Based on modern lake morphology, climate and runoff data, and the elevations recorded by the shoreline facies identified within the marginal Holocene sedimentary sequence, we constructed a paleohydrologic balance model and a precipitation curve. According to the model, annual precipitation may have been fallen below 460 mm during the 8.2 ka event, and 468–478 mm during the 4.2 ka and 3.2 ka events – demonstrating an extreme decrease in precipitation compared to the earlier wet phases. In turn, Holocene Archaeology in West Anatolia outlines (i) a widespread abandonment and/or notable fire events at the end of the Early Bronze Age III (ca. 4.2 ka), and (ii) a high level of social instability at the beginning of the Early Iron Age (ca. 3.2 ka). The correlation between the timing of lake level falls at Simav (water volume depletion caused by drying trends) at 8.0 ka, 3.9 ka and 2.8 ka and cultural fluctuations suggest that drought events may have played a major role in these socio-political changes in western Anatolia. Furthermore, the high lake-level stages (associated with precipitation >500 mm) coincide with the Late Chalcolithic to Early Bronze Age I transition as well as the Hellenistic and Roman periods, both times of economic stability and growth in the region.