Stratigraphic and Sedimentological Characteristics of Jurassic–Lower Cretaceous Sediments at Kösrelik–Kösrelikiziği (North of Ankara, Turkey)
Jurassic–Lower Cretaceous rocks to the northeast of Ankara (central Turkey) were deposited in a tectonically controlled basin that was aligned SW–NE. Vertical and lateral lithological variations in the sequence resulted from synsedimentary tectonism. The Jurassic–Lower Cretaceous sequence in the study area overlies the weakly metamorphosed Late Triassic rocks (the Karakaya Complex) with an angular unconformity. The sequence begins with interbedded deltaic conglomerate and sandstone (the Çoraklıktepe Member). The Sinemurian–lower Pliensbachian sandy limestone overlies the coarse sandstone with both a lateral and vertical transition. The sandy limestone is red in colour and highly fossiliferous. Crinoidal limestone and ammonite-bearing marl rest on the sandy limestone, signifying a rapidly deepening depositional environment. It is overlain by red marl containing brachiopods and bivalve coquina interbeds. The intermediately bedded pseudonodular limestone with abundant ammonites, crinoids, brachiopods, and bivalves is found above the red marl. Following synsedimentary tectonism, thick nonfossiliferous mudstone was deposited over the ammonite-bearing rocks (the Uzundere Member), indicating that the area shallowed during the early Pliensbachian. During the late Pliensbachian–early Toarcian, detritic rocks were deposited followed by a progressive change to deposition of variegated red limestone. This typical ammonitico-rosso facies wedges laterally into green mudstone (the Beytepe Member). After the Bajocian, the area rapidly shallowed and thick interbedded sandstone and mudstone (the Turnaçeşme Member) were deposited over the entire basin. Due to post-Callovian block faulting in the area, the base topography of the basin was changed. For that reason, in the northern part of the study area, the pelagic carbonate platform sediments (the Çakırlardere Formation) containing abundant ammonite and pelagic oolite were deposited directly onto the basement rocks. This points to the development of shallow areas offshore as a result of synsedimentary faulting. The pelagic ooid-bearing limestone grades laterally and vertically into cherty limestone. During the Oxfordian–Early Cretaceous, the area deepened and limestone with Radiolaria (the Soğukçam Formation) was deposited.
KeywordsAnkara Jurassic Ammonitico-rosso Pelagic oolite PCP Hardground
- Alkaya, F. (1998). Kösrelik–Kızık (Ankara) Alanı Sinemuriyen–Bajosiyen (Alt-Orta Jura) Istifinin Ammonit Faunası ve Stratigrafisi, Cumhuriyetin 75. yıldönümü Yerbilimleri ve Madencilik Kongresi Bildiri özetleri, 137–138 (in Turkish).Google Scholar
- Deli, A. (2005). Alacaatli-Beytepe-Etimesgut (GB Ankara) Bölgesi Jura-Kretase Çökellerinin Sedimantolojisi. Selçuk Üniv.Fen Bil. Enst. Doktora tezi, p. 233 (unpublished, in Turkish).Google Scholar