Precipitation gradients during the Miocene in Western and Central Turkey as quantified from pollen data

In the present paper, we have analyzed thirty-five palynofloras covering the time span from the Early Miocene (Aquitanian) to the Late Miocene (middle Tortonian) in Turkey. The results obtained are presented in tables and maps showing temporal palaeoprecipitation values. The mean annual precipitation (MAP) exceeds 1200 mm during the Aquitanian and early-middle Serravallian. It is suggested to have been between 1000 and 1300 mm in the latest Serravallian-earliest Tortonian in Western and Central Turkey. In the early-middle Tortonian, the lower boundary of MAP decreases to below 1000 mm in Central and Eastern Turkey. Today, MAPs are represented by lower values around 600-1000 mm in Western and 400-600 mm in Central Turkey. For the driest month (LMP), the rainfall was not distributed homogeneously. In the Aquitanian, the calculations are between 36 and 48 mm with humid conditions in Western and Eastern Turkey. During the Burdigalian and Middle Miocene, the driest month precipitation varied with respect to locations. However, it is clear that there was a reduction in precipitation during the early-middle Tortonian, with values around 26-27 mm in Central and Eastern Turkey. The same pattern is observed for the wettest month precipitation (HMP), with estimates higher than 200 mm during the Aquitanian and earliest Tortonian, although some areas received low rainfall. HMP was reduced between 130 and 140 mm in the early-middle Tortonian. The warmest month precipitation (WMP) varied from 96 to 140 mm except for Konya-Ilgin, Kirsehir-Hacibektas and Manisa-Soma that received 88 mm during the Early-Middle Miocene. In the early-middle Tortonian, the amount of summer rainfall lay between 58 and 88 mm. The reason of the decrease in all rainfall parameters during the early-middle Tortonian could be related to several factors such as climatic cooling, altitude, aridification, palaeotopograhy or continentality. However, it is necessary to indicate that the Tortonian cooling had previously been proposed by Akgun et al. (2007) as the explanation, using a large number of palynological assemblages in Turkey. We also observe a decrease in precipitation parameters during the Middle Miocene. This could be related to fact that either low species diversity can result in wide coexistence intervals or the Monterey cooling event was related to a cooling during the Langhian and Serravallian. (C) 2010 Elsevier B.V. All rights reserved