DRAINAGE EVOLUTION DURING THE UPLIFT OF THE CENTRAL ANATOLIA PLATEAU

Abstract:

The Central Anatolian plateau formed in the past 8-6 Myrs, associated to a change in tectonic regime, from contraction to extensional escape tectonics. We have examined the response of the river drainage of Central Anatolia to the rise of the plateau uplift and to the formation of the Anatolian microplate, tracking changes in drainage organization. Anatolia experienced widespread rock uplift and erosion in the Late Oligocene, generating a narrow, steep, and quickly eroding mountain range above the future southern plateau margin. A regionally widespread marine transgression resulted from wholesale foundering of this orogen in Early Miocene time. Widespread planation surfaces overlapped by Miocene marine carbonates bevel this topography, indicating that relief had been reduced to a low elevation pedimented landscape by the end of the Middle Miocene. Plateau uplift initiated around 11 My ago in Eastern Anatolia; it was echoed in Central Anatolia by a short-lived phase of contraction and localized uplifts that predate escape tectonics and mark the beginning of the current topographic differentiation of the southern plateau margin. The through-going drainage network inherited disintegrated, and a vast zone of inward drainage formed at the location of the future plateau interior. Between 8 and 6 My, the southern plateau margin (i.e. the Tauride Mountains) emerged. δ¹⁸O analyses on lacustrine and pedogenic carbonates show that the southern plateau margin, if not the plateau interior, had experienced enough uplift by 5 My to generate a substantial rain shadow over the plateau interior. Being disconnected from the regional base level from the start, the plateau interior was able to rise without experiencing substantial dissection. It reconnected to all surrounding sediment sinks (Mediterranean Sea, Black Sea and Persian Gulf) over the past 5 My. We discuss the mechanisms that have driven this reconnection. Bottom-up processes of integration such as drainage divide retreat did not produce any major changes. Top-down processes such as lake overflow and avulsion achieved most of the re-integration. They result from more positive precipitation/evaporation balances, either due to elevation change during plateau uplift or due to tectonic fragmentation of depocenters during the development of escape tectonics.