Cretaceous geological evolution of the Pontides

Abstract

Abstract The Pontides forming the southern continental margin of the Black Sea consist of the Strandja, İstanbul and Sakarya zones. The Zonguldak-Ulus Basin, located in the NE part of the İstanbul Zone, has traditionally been viewed as opening during the Barremian and deepening until the Albian under the control of normal faults. New outcrop data indicate that the southern and eastern parts of this basin facing towards the Intra-Pontide Ocean in the south were already open during the Berriasian or earlier. Uplift and erosion of the Zonguldak-Ulus Basin during the Cenomanian is attributed to collision of the İstanbul and the Sakarya zones along the Intra-Pontide Suture. The Sinop Basin in the Sakarya Zone opened during Hauterivian–Barremian time. Sedimentation in this basin continued in a deepening environment until the development of the Pontide Magmatic Belt during the Turonian. The contact between the İstanbul and the Sakarya zones is represented by a shear zone that consists of siliciclastic distal turbidites, debris-flow deposits and radiolarian cherts imbricated with Middle Jurassic–Lower Cretaceous magmatic arc fragments. This shear zone is interpreted as being the eastern continuation of the Intra-Pontide Suture, separating the İstanbul and the Sakarya zones. The Western Black Sea Basin to the north of the Pontides possibly opened in two stages. In the first stage, coeval with the opening of the Zonguldak-Ulus Basin, the rifting was a wide-rift style and caused thinning of the continental crust. During the Turonian–Santonian, the Pontide Magmatic Belt started to develop as an extensional arc, and caused break-up of the already thinned crust and the start of oceanic spreading in the Western Black Sea Basin.