Facies characteristics of Jurassic–Lower Cretaceous successions at Kösrelik–Kösrelikızığı (North of Ankara, Turkey)

Abstract

Jurassic–Lower Cretaceous rocks in the Kosrelik and Kosrelikizik areas (North of Ankara, Central Turkey) which were deposited in a tectonically controlled basin have outcrops in a very restricted area but they carry very important evidences for elucidating the Late Jurassic paleogeography of the Ankara region subjected to heavy tectonic activities during Hettangian–Oxfordian, especially during Sinemurian. Detailed facies analysis of sequences in the study area indicates that the deposition took place in two different tectonically controlled depositional settings, 3 km apart from each other. At the east of the study area, the succession is represented by Hettangian–Sinemurian aged basin sediments lying on the basement rocks with angular unconformity, but succession at the west comprises sediments of Oxfordian pelagic carbonate platform (PCP) overlying the basement rocks with angular unconformity. The PCP sediments were overlapped by radiolaria bearing pelagic limestone, Oxfordian–early Cretaceous in age, under relatively calm environmental conditions. Anomalies in C and O isotopes, trace elements and rare earth element values coincide with the periods of fast changes in the environmental conditions. The sedimentological and geochemical data indicated that the area was deepened and shallowed several times until early Cretaceous.