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

This study provides a new magnetostratigraphy for the stratigraphic interval that includes the late Miocene Haliminhani and Hayranli 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 Haliminhani and Hayranli 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 Haliminhani and Hayranli fossil mammal-bearing levels. Published bulk carbonate delta C-13 and delta O-18 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 delta C-13 and delta O-18 values shows two intervals of increased delta C-13 (by ca. 6-8 parts per thousand) that are followed by a similar decrease over total time intervals of ca. 150 kyr. The increase in delta C-13 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 delta O-18 during peaks in delta C-13 make temperature an unlikely driver and we surmise that adjustments to nutrient input to the basin were responsible for changes in delta C-13. Overall, the results suggest that the Pikermian chronofauna of the Sivas Basin thrived under relatively stable local hydrological and climatic conditions. At Haliminhani, 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.

Automated summary

This study presents a new magnetostratigraphy for the late Miocene period in the Sivas Basin, Turkey. The findings suggest that the Pikermian chronofauna thrived under stable hydrological and climatic conditions in the basin, and it shares high faunal similarities with the European Mammal Neogene.