Mammal bearing late Miocene tuffs of the Akkaşda?? region; distribution, age, petrographical and geochemical characteristics

Abstract

The Neogene tuffs of the Akkaşda?? region, in the south eastern part of the Çank?r?-Çorum Basin in Central Anatolia, yielded one of the richest mammalian faunas of Turkey. The main aim of the present study is to provide data on the distribution, age, petrographical, mineralogical and geochemical composition of these tuffs. It is shown that they are primary products of a volcanic process. The Akkaşda?? tuffs are included in a late Miocene sedimentary sequence and were deposited as pyroclastic flow deposits. The gas escape structures (gas segregation pipes) in tuffs and the abundance of pumice and lithic clasts in the lower parts should be mentioned. The age of the tuffs is determined as late Miocene (MN 12 zone) based on the rich mammalian fauna and as 7.1 ± 0.1 Ma on the basis of radiometric dating. The petrographic investigations indicated that the Akkaşda?? tuffs are vitric tuffs. Biotite and lithic clasts occur in a glassy matrix. In addition, they contain feldspar (orthoclase), quartz phenocrysts, oxyhornblende and pumice clasts. With these properties, the tuffs present all characteristics of ignimbrites. Geochemical analyses reveal the calc-alkaline nature and rhyolitic composition of these tuffs. These results show that the Akkaşda?? tuffs show similarities to those of the Nevşehir Plateau which belong to the Central Anatolian Volcanic Province. Because these tuffs are pyroclastic flow deposits, it is thought that the source area should be close to Akkaşda??. Volcanic activity might have caused the mass death of mammals the remains of which are concentrated in several bone pockets. © Publications Scientifiques du Muséum national d'Histoire naturelle, Paris.