Evidence for enhanced aridification since 13 Ma in the Qom back-arc basin, Central Iran

The Iranian Plateau was once occupied by the Neotethys Sea, which connected with the Indian Ocean in the southeast and the proto-Mediterranean in the west during most of the Cenozoic era. However, the Neotethys Sea has undergone a stepwise retreat, and the Tethyan Seaway also closed in the Miocene driven by both Arabia Eurasia collision and global eustatic sea-level drop. Changes in the land-sea distribution and uplift of the Zagros Mountain belt must have affected paleoclimatic changes in Iran. To date, a high-resolution paleoclimatic record is lacking for Iran. In this paper, we present new environmental magnetic and color parameter data for terrestrial sediments in the Qom back-arc basin, Central Iran from the middle to late Miocene (17-11.5 Ma). All of our parameters indicate an abrupt climatic change at-13 Ma. We suggest that the less reddish color and a shift in environmental magnetic parameters after-13 Ma implies weakened chemical weathering under a colder/drier climate. Enhanced aridification was mainly controlled by closure of the Tethyan Seaway and shrinkage of the Neotethys Sea after-13 Ma, which greatly reduced moisture transport to the downwind Central Iran by westerlies, whereas the rain shallow effect of the initially uplifted Zagros Mountain belt and reduced seawater evaporation related to lower sea-surface temperatures after the Mid-Miocene Climatic Transition only played minor roles. Therefore, our results provide a window to discuss relationships between plate tectonic movements, land/sea distribution, and climatic change in a tectonically active region during the late Cenozoic.