Tectonic development of the southern Karasu Valley, Turkey: successive structural events during basin formation
New fault data are presented for the Karasu Valley, southern Turkey. Field measurements concentrate on the Eocene–Miocene (c. 48–7 Ma) sediments exposed on the south-western rift margin, in order to investigate the early development of this basin. Fault data show two trends in orientation NW–SE and NE–SW with a subordinate north–south trend. Stress inversions combined with field relationships indicate at least three phases of faulting. Firstly, an extensional event characterized by NE–SW and NW–SE normal faults, which are interpreted to have formed owing to flexural uplift in the forebulge region to the Bitlis–Zagros collisional front prior to the Middle Miocene. Secondly, north–south normal faults invert to give a stress ratio [R=(σ2 – σ3/σ1 – σ3)] indicative of an extensional stress regime, transitional to strike-slip faulting. The final stress phase (Pliocene–Recent) is of strike-slip faulting and east–west-trending normal faulting. This stress regime is interpreted as the result of the propagation of the Dead Sea Fault or East Anatolian Fault. Previous models of rift formation have invoked either transpressional or transtensional origins for the area; the new data presented here indicate that the southernmost Karasu Valley developed through extension followed by transtension.