ORIGINAL Quaternary evolution of the Gulf of İzmit (NW Turkey): a sedimentary basin under control of the North Anatolian Fault Zone Erdal Dolu & Erkan Gökaşan & Engin Meriç & Mustafa Ergin & Tolga Görüm & Hüseyin Tur & Berkan Ecevitoğlu & Niyazi Avşar & Muhittin Görmüş & Fatmagül Batuk & Buğser Tok & Oktay Çetin Received: 20 February 2006 / Accepted: 16 January 2007 / Published online: 27 February 2007 # Springer-Verlag 2007 Abstract The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started to accumulate during a progradational phase, in a south-facing half- graben. A coarse-grained sedimentary unit prograding into the gulf from the south since 200 ka B.P . indicates a Geo-Mar Lett (2007) 27:355–381 DOI 10.1007/s00367-007-0057-3 E. Dolu Institute of Marine Science and Management, Istanbul University, Vefa, 34470 Istanbul, Turkey E. Gökaşan (*) : T. Görüm Natural Science Research Center, Yıldız Technical University, Beşiktaş, 34349 Istanbul, Turkey e-mail: egokasan@yildiz.edu.tr E. Meriç Moda, Hüseyin Bey Sok. 15/4, Kadıköy, 34710 Istanbul, Turkey M. Ergin Faculty of Engineering, Department of Geological Engineering/ Geological Research Center for Fluvial, Lacustrine, and Marine Environments (AGDEJAM), Ankara University, Tandogan, 06100 Ankara, Turkey H. Tur Faculty of Engineering, Department of Geophysical Engineering, Istanbul University, Avcılar, 34850 Istanbul, Turkey B. Ecevitoğlu Department of Geophysics Engineering, Ankara University, Tandoğan, 06100 Ankara, Turkey N. Avşar Engineering-Architecture Faculty, Geology Department, Çukurova University, Balcalı, 01330 Adana, Turkey M. Görmüş Engineering-Architecture Faculty, Department of Geology, Süleyman Demirel University, Çünür, 32100 Isparta, Turkey F. Batuk Faculty of Civil Engineering, Department of Geodesy and Fotogrametric Engineering, Yıldız Technical University, Beşiktaş, 34349 Istanbul, Turkey B. Tok Department of the Navigation, Hydrography and Oceanography, Turkish Navy, Çubuklu, 81647 Istanbul, Turkey O. Çetin Science-Lettres Faculty, Department of Physics, Abant İzzet Baysal University, Gölköy, 14280 Bolu, Turkey