HOW CAN CONTINENTAL COLLISION AFFECT TO DEPOSITIONAL SETTINGS: A REVIEW FOR GEOLOGICAL EVOLUTION OF THE SOUTHERN SAKARYA BASIN, NW TURKEY

Study area is located between Göynük (Bolu) and Nallıhan (Ankara), NW Anatolia, to the north of the Neotethyan (Izmir-Ankara-Erzincan) Suture Zone. Southern part of Sakarya basin illustrates uninterrupted sedimentation from Middle Jurassic to Miocene. Middle Jurassic-Lower Cretaceous age pelagic limestones of the Soğukçam Formation is the oldest rock, overlain by the Cenomanian-Campanian age turbiditic Yenipazar Formation and the Maastrichtian age Taraklı Formation shallow marine sandstones with benthical foraminiferas and rudists. Over the Taraklı Formation lies conformably the Kızılçay Group terrestrials, and it exhibits varying facies from north to south of the study area. Coral-bearing Lower Paleocene Selvipınar Formation occurs in the north. 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 of the study area during the Lower Paleocene-Eocene.

The Soğukçam and Yenipazar Formations represent deep marine conditions, while the Taraklı Formation a shallow one in fore-arc basin. This indicates the region underwent a rapid uplift due possibly to initial collision and overthrusting. The Taraklı Formation is seen as a fine-grained sandstone facies in the north; while it is seen as conglomerates with shallow marine sandstones in the south. In the post-Maastrichtian age units, the occurrence and lateral transitions of shallow marine and terrestrial sediments 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. These differences and tectonic consequences represents two different K-T transitions: From shallow marine to terrestrial settings in the south; from marine to shallow marine in the north. It is possible observing the K-T transition between terrestrial settings in south of study area. 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