Magnetostratigraphy of the Pikermian fauna-bearing late Miocene Sivas Basin (central Anatolia, Turkey): fluvio-lacustrine sedimentation under stable climatic conditions across the Tortonian-Messinian boundary

Abstract

This study provides a new magnetostratigraphy for the stratigraphic interval that includes the late Miocene Haliminhanı and Hayranlı mammal fossil assemblages of the Sivas Basin (central Anatolia, Turkey). The fossil assemblages show high faunal similarities to the Pikermian chronofauna, which forms part of the Old World Savannah Paleobiome that formed during a time of global cooling, aridification, and grassland expansion. Previous biostratigraphic age estimates placed the fossil horizons within European Mammal Neogene (MN) zones MN11-MN12, which tentatively places the Anatolian Haliminhanı and Hayranlı localities in the ca. 9 to 7 Ma time interval. Nearby dated sites harboring Pikermian fauna in Turkey, Greece, and Bulgaria range in age between 11 and 7.3 Ma. Our new magnetostratigraphy in 140 m thick fluviolacustrine deposits refines the age estimate for the Sivas Basin to 8.0–6.5 Ma for the Haliminhanı and Hayranlı fossil mammal-bearing levels. Published bulk carbonate δ13C and δ18O values of the fluvio-lacustrine beds indicate a positive water balance and suggest no significant long-term changes in hydrology and primary productivity within the former Sivas Basin lake. Further inspection of the δ13C and δ18O values shows two intervals of increased δ13C (by ca. 6–8‰) that are followed by a similar decrease over total time intervals of ca. 150 kyr. The increase in δ13C in a lacustrine carbonate can be related to an increase in biogenic productivity, which may result from changes in nutrient input and temperature. The absence of simultaneous changes in δ18O during peaks in δ13C make temperature an unlikely driver and we surmise that adjustments to nutrient input to the basin were responsible for changes in δ13C. Overall, the results suggest that the Pikermian chronofauna of the Sivas Basin thrived under relatively stable local hydrological and climatic conditions. At Haliminhanı, the Pikermian fauna flourished well into the Messinian, as opposed to Greek and Bulgarian sites where faunal turnover was proposed to have occurred under a cooling climate and aridification across the Tortonian-Messinian boundary.