Oligocene to Pliocene palaeogeographic evolution of the Çankırı-Çorum Basin, central Anatolia, Turkey

The Çankırı-Çorum Basin is one of the largest basins of Central Anatolia to have developed Oligocene to Quaternary terrestrial environments. The basin contains significant raw materials for industry and energy, but the determination of their distribution patterns requires a good knowledge of the stratigraphic and spatial distribution of deposits. Besides, evolving tectonic regimes in the basin and the sedimentary sequences controlled by them can play key roles in revealing the regional paleogeography. On the basis of a new chronological framework provided by mammalian fossils and sedimentological data, ten sedimentary formations have been identified for the Oligocene-Pleistocene time interval. From the oldest to the youngest these are the Ä°ncik, Güvendik, Kızılırmak, Kılçak, Kumartaş, Hançili, Bayındır, Akkaşdağı, Bozkır and Değim formations. During Early Oligocene times, an alluvial fan and braided and meandering rivers deposits developed at the northern and eastern rims of the basin, whereas lacustrine products dominated by evaporitic deposits occurred in vast areas at the center. In Late Oligocene, the lake area contracted and dominant floodplains and braided rivers took place in the central area of the basin. During Early-Middle Miocene, large lacustrine areas dominated by organic/clastic deposits developed in the northern and middle parts of the basin; lake shore facies were formed in northern parts of the basin and on some paleohighs surrounding the lake. In the Orta and Şabanözü regions volcanic activity started during the Middle Miocene and lasted until the beginning of Late Miocene. During Late Miocene, there were different types of lacustrine environments in the northern and southern parts of the basin: a hypersaline lake characterized by evaporitic deposits in the north and carbonate-rich shallow lakes and swamps in the south. A younger evaporitic lake formed in Early Pliocene in the northern part of the basin and covered vast areas. Its deposits are as thick as 400 m. From Late Pliocene, the thick sedimentary sequences deposited during the Oligocene-Early Pliocene interval become fragmented and deformed by a tectonic wedge bounded by a normal fault in the west and a thrust in the east. Sedimentary products of this tectonic regime are represented by thick alluvial fan sequences of the Değim Formation.