The Late Cenozoic evolution of the eastern Aegean is dominated by widespread continental extension. The most prominent structures are E-W- and NE-SW-trending grabens and intervening horsts, while NW-SE- and N-S-trending faults form the other less important structures. This paper documents the results of recent geological mapping and structural and stratigraphical analysis from the Halitpasa half graben, which forms the northwestern continuation of the Gediz Graben. Field evidence for a new NW-SE-trending dextral wrench-dominated fault zone (here named the Halitpasa transpression zone), which involved the thrusting of pre-Palaeogene basement onto Upper Miocene-Lower Pliocene sediments, is presented. The fault zone is correlated with the timing of a major unconformity that separates Upper Miocene-Lower Pliocene lacustrine sediments (Develi and Halitpasa formations) from overlying late Early Pliocene, distal alluvial-fan sediments (Kizildag Formation). The field relations and mammalian data suggest an early Early Pliocene age for this unconformity. The manuscript therefore documents structural evidence for a compressive phase during the evolution of active continental extension in western Turkey. The deformation is attributed to the known Early Pliocene compressive pulse of the Aegean Arc.