LATE CENOZOIC PALEOENVIRONMENTAL ISOTOPE RECORDS OF THE CENTRAL ANATOLIAN PLATEAU, TURKEY

The geochemistry and sedimentology of lacustrine and pedogenic carbonates are a powerful tool to reconstruct paleoclimatic and paleoecological conditions of the environment in which they formed. Sedimentological and oxygen and carbon stable isotope analyses were carried out on Neogene to Quaternary carbonate nodules from paleosols and lacustrine carbonates in the Central Anatolian Plateau (CAP). At current, there is no consensus about the Cenozoic environmental dynamics in Central Anatolia mainly because quantitative information on late Neogen climate, lake hydrology and timing of the uplift of the Tauride Mountain range bordering the plateau are missing. Here we use carbonate δ¹⁸O values to reconstruct oxygen isotopic compositions of Neogene meteoric waters and compare these records to the modern isotopic pattern of surface waters on the CAP.

The oxygen isotopic composition of lacustrine and pedogenic carbonates indicates that most of these carbonates formed from water with δ¹⁸O values approximately 3 to 8 ‰ more positive compared to recent meteoric water on the plateau. This depletion in ¹⁶O can be attributed to mainly two effects: stronger plateau evaporation and/or a weaker rainshadow. Field observations, such as evaporate minerals in the lacustrine limestones, and analytical results indicate, especially in the north of the CAP interior (Ankara area), an arid climate with shallow, hydrologically closed, saline lakes in the Neogene. At the southern margin of the plateau (Ecemiş Fault Zone) Neogene lakes were probably hydrologically transient with reconstructed meteoric water δ¹⁸O values being ~ 5 ‰ more positive than the modern values, overall suggesting that rainshadow development post-dated deposition in the Neogene Ecemiş Fault Zone basins.