LATE MIOCENE TO PLIOCENE PALEOENVIRONMENT AND SURFACE UPLIFT OF THE CENTRAL ANATOLIAN PLATEAU AND ITS SOUTHERN MARGIN (TURKEY)

The Central Anatolian Plateau (CAP), Turkey, is bordered to its south and north by steep mountain belts that emerged ~8-7 m.y. ago from the Mediterranean and Black Seas and currently form orographic barriers. We document and quantify surface uplift of the southern CAP margin by providing an oxygen isotope-based paleoclimate and -elevation reconstruction of lacustrine carbonate from Upper Oligocene to Pliocene continental basins in the CAP interior. Knowledge of the onset, duration and rate of orographic barrier formation is crucial for understanding the geodynamic drivers of surface uplift, as well as the impact of surface uplift on climatic conditions. The geochronological framework is based on existing mammal, radiometric and paleomagnetic age constraints, as well as new ⁴⁰Ar/³⁹Ar and paleomagnetic data. Our preliminary paleoenvironmental and -temperature reconstruction is based on δ¹⁸O, δ¹³C and br-GDGTs (branched Glycerol-Dialkyl-Glycerol-Tetraethers) records from soil and lacustrine carbonates.

We interpret the gradual ~4 ‰ decrease of δ¹⁸O values of lacustrine carbonate in the southern plateau interior between ~11 and 5 Ma to reflect the Late Miocene development of an orographic barrier along the southern plateau margin. Estimated paleoelevations indicate that the orographic barrier reached present-day elevations of ~2 km by 5 Ma. The timing of surface uplift and contraction in the forearc suggests that subduction beneath Anatolia and associated crustal shortening was the main driver of surface uplift.

The chronologies of the sampled sections indicate that lacustrine sedimentation in the eastern CAP ceased by ~5-4 Ma; δ¹⁸O records provide no evidence for an evaporative regime during final sedimentation. The eastern CAP is currently drained by rivers to the Black Sea, the Mediterranean and the Persian Gulf, and stratigraphic relationships show that river incision predates ignimbrite emplacement at 3 Ma. Therefore, lake avulsion and river incision may have led to drainage of the lake system. Mean δ¹³C values in lacustrine and soil carbonates drop from +2 to -8 ‰ between ~11 and 5 Ma. We seek to interpret the 10 ‰ drop in mean δ¹³C values during a time of surface uplift and increased aridity in the Eastern Mediterranean, as well as a turnover from tropical evergreen to deciduous forest and woodland vegetation.