MIOCENE TO PLIOCENE PLATEAU DEVELOPMENT AND PRECIPITATION PATTERNS IN CENTRAL ANATOLIA

Long-term stable isotope records of continental depositional systems represent increasingly important tools for paleoenvironmental, paleoclimatic, and paleoaltimetric reconstructions within continental interiors. A rapidly growing number of studies within the Earth’s major mountain ranges has demonstrated that the growth of topography and orogenic plateaus profoundly influences local, regional, and hemispheric climate and hence precipitation patterns. In contrast, such records are almost absent for the Anatolian plateau, an important topographic element in the Alpine-Himalayan chain and an area most likely to be strongly affected by future climate change and water scarcity.

Here, we present oxygen, carbon, and hydrogen isotope data from Neogene-to-recent fluvio-lacustrine and pedogenic environments, stream and lake waters with the ultimate aim of reconstructing past precipitation changes, plateau aridification and ideally surface uplift histories of the Neogene Central Anatolian Plateau (CAP). Our long-term objective is to assess the role of climatic and orographic factors that have governed the distribution (and isotopic composition) of precipitation across the CAP from the Neogene to recent. Such data is fundamental for our understanding of the geodynamic and sedimentary history of orogenic plateaus in general and for the role of surface uplift along the plateau margins in the Pontide and Tauride mountains. Our approach is to cross-calibrate modern patterns of isotopes (oxygen and hydrogen) in precipitation with pedogenic carbonate oxygen and carbon isotope data across topographic barriers that today strongly control the distribution of rainfall along the plateau margins and within the plateau interior. We then compare these patterns with Miocene-to-Pleistocene lacustrine and pedogenic records to assess a) the role of late Neogene (ca. 8-0 Ma) surface uplift in the Pontide mountains, b) the importance of rain shadow development in the lee of the plateau margins, and c) the potential effects of Mediterranean aridification during the Messinian (at ca. 5.9 to 5.5 Ma).

Based on ca. 200 hydrogen and oxygen isotope data from modern streams and rivers we can document the orographic effect of the southern plateau margin onto the hydrogen and oxygen isotopes in precipitation with apparent oxygen isotope lapse rates that fall within the global average (0.2-0.4 ‰/100 m) and a leeward decrease in the oxygen isotope ratios of ca. 3-4 ‰ compared to sea level.

Miocene-to-recent lacustrine and pedogenic carbon and oxygen isotope profiles from the southern plateau margin into the plateau interior (Ermenek, Ankara, Cankiri, Kastamonu basins) document that to first-order similar-to-modern lake isotope records characterize the late Neogene with strongly evaporative lake systems dominant in the Pliocene. We specifically focus on fault-bounded basins in the Ecemis basin immediately behind the southern plateau margin. Here, our data indicate that surface uplift of the souther plateau margin (and hence the Pontide Mountains) most likely occurred in a time-transgressive fashion with the western termination clearly characterized by a phase of relatively young (8-5 Ma) surface uplift. This pattern is less obvious further East where lacustrine and pedogenic isotope records are consistent with a phase of earlier (Early to Mid-Miocene) rain shadow development. Based on our current long-term stable isotope data we preliminarily conclude that surface uplift of the Central Anatolian Plateau occurred at different rates and magnitudes along the Pontide Mountains which places indirect constraints on plate boundary and mantle dynamics but also hosts a series of questions regarding animal and plant migration, changes in precipitation-controlled plant communities and ecosystems as well as late Neogene biodiversity in the Eastern Mediterranean region.

The data presented here are part of the ESF Eurocores TopoEurope inititiative: “Vertical Anatolian Movements Project”.