CRETACEOUS-PALEOGENE DEPOSITIONAL SETTINGS AND GEOLOGICAL EVOLUTION OF THE SOUTHERN SAKARYA ZONE, NW TURKEY

The Göynük (Bolu) and Nallıhan (Ankara) area, NW Anatolia, lies to the north of the Neotethyan (Izmir-Ankara-Erzincan) Suture Zone. It comprises units ranging from the Jurassic to Miocene ages. Middle Jurassic-Lower Cretaceous age pelagic limestone of the Soğukçam Formation is the oldest exposed rock unit, overlain by the Upper Cretaceous Gölpazarı Group. The Gölpazarı Group includes the Cenomanian-Campanian age turbiditic Yenipazar Formation and the Maastrichtian age sandstones of the Taraklı Formation. Over the Taraklı Formation lies conformably the Kızılçay Group, and it exhibits varying facies from north to south of the study area. In the north, there occurs the coral-bearing Paleocene Selvipınar Formation. In the south, instead, there are clastics of the Kızılçay Group overthrust by the Soğukçam Formation. Clastics and bituminous shales of the Kızılçay Group indicate a terrestrial setting in the study area during the Lower Paleocene-Eocene.

The Soğukçam and the Yenipazar Formations represent deep marine conditions, while the Taraklı Formation a shallow one with a rudist, mikro and macrofossil content. This indicates the region underwent a rapid uplift due possibly to initial collision and overthrusting during pre-Maastrichtian times. The occurrence and lateral transitions of shallow marine and terrestrial sediments in the post-Maastrichtian age units suggest a progress of uplift, but at different rates at different locations; at a relatively fast rate in the south and a slow rate in the north. The presence of tectonic features such as E-W oriented folds, overturned folds and faults are related to shortening during a collisional stage that affected the whole region.