Tectonic evolution of the central part of Nallihan wedge (Nallıhan-Cayirhan, Ankara)

Related to rifting, the basin began to deepening and the neritic limestones of the Soğukçam Formation deposited. Ocean became deeper and deep sea shales of the Yenipazar Formation were deposited. At the end of Upper Cretaceous, the basin started to become shallow and even the region locally eroded due to the uplift. These events indicate the closure of the Neo-Tethys Ocean. The data about the Cretaceous-Eocene period is limited in the study area. The study area is situated in the south of the Intra-Pontide Ocean. The Karakaya Complex exists between the Intra-Pontid and İzmir-Ankara oceans. There is no Paleocene unit in the study area. Because of the collision, the sea had almost disappeared at the end of the Lower Eocene and erosion and sedimentation had started at the same time. The conglomerates of Kızılçay Formation contains metamorphic pebbles which indicates the uplift of the basement units during the closure of Intra-Pontide Ocean. In the Middle Eocene, the region had become a ramp basin and the andesitic and rhyolitic volcanism increased related to the collision activity. The shallow sea environment was still in the northwestern part of the basin in this period. This basin had tightened, uplifted and become folded by the reason of the N-S compression and eroded until Early Miocene. During this event, unconformable contact between Karakaya Complex and Kızılçay Formation was structurally dislocated. At the same time, eastern part of the basin had become an intermontane basin. N-S-trending compressional regime had turned into NNW-SSE-trending regime during Lower-Middle Miocene and in the meantime the basin was a swamp/lake. Associated with this compressional regime, the Eocene units continued to uplift and they gave material to the Miocene rocks by means of erosion. The Neogene basin started to uplift and the environment evolved to a river in the Upper Miocene. For this reason, Lower-Middle Miocene and Upper Miocene units display local unconformities in the region. Open folds had formed in the Lower-Middle Miocene rocks and this unit started to erode in Upper Miocene because of the compression. In the Pliocene, the basin was dominated by alluvial fans and river.