The lithostratigraphy of the Mekece-Iznik Corridor, the Geyve-Pamukova, and the Iznik basins on the southern branch of the North Anatolian Fault System (NAFS-SB) was investigated in detail. The intra-basin deposits carried by Sakarya River and the drainage systems in the northern and southern elevated blocks of the Iznik and Geyve-Pamukova Basins have been classified based on their lithofacies characteristics. The Geyve-Pamukova basin, which has developed with a NNE-SSW-trending transtensional strain, was formed as a lazy Z-shaped and releasing bend or pure strike-slip, pull-apart basin that is related to simple-shear, right-lateral strike-slip faulting. The Iznik basin was formed by a right-lateral strike-slip faulting kinematics and NNE-SSW-trending transtension as a result of the step-over of the northeast-trending DA +/- razali fault from the southern edge to the NW-trending Gurle fault, and the western step-over of this fault to the E-W-trending Umurbey fault. This strike-slip setting is also supported by the NW-SE-trending right-lateral oblique normal Orhangazi fault on the northern edge of the basin. According to this, the Iznik basin can be described as a more advanced stage of a large-scale, pull-apart basin compared with a lazy Z-shaped and releasing bend or transtensional strain. Furthermore, it is defined as the former stage of an extreme or rhomboid-type transtensional pull-apart basin.