Middle Pleistocene tectonic events around the SE Aegean Sea: Insights from magnetostratigraphy, (U–Th)/He zircon dating, and fault kinematics in the Datça Graben (SW Türkiye)

Abstract

This study constrains the stratigraphy, age, and tectono-sedimentary evolution of the Datça Graben (southwestern Turkey) through integrated magnetostratigraphy, zircon (U-Th)/He geochronology, sedimentological analysis, and fault kinematic studies. The basin, developed along the southwestern margin of Anatolia under N-S extension, preserves ~ 350 m of fluvio-lacustrine to shallow-marine deposits, primarily assigned to the Yıldırımlı Formation. Two interbedded tuff layers yield zircon (U-Th)/He ages of 1.56 ± 0.10 Ma and 1.44 ± 0.10 Ma, constraining deposition between 1.78 and 0.78 Ma (Calabrian Age) when correlated to the Geomagnetic Polarity Time Scale. Magnetostratigraphy records a reversed-normal-reversed polarity sequence within subchrons C1r.2r, C1r.1n, and C1r.1r. The basin fill dips southward, with thicker accumulations along the southern boundary fault, indicating an asymmetric half-graben geometry dominated by southern-margin subsidence. Syn-depositional growth faults, paleostress analysis, and mesoscopic fault kinematics indicate persistent N-S extension with minor azimuthal variations (NNW-SSE to NE-SW). Paleomagnetic declination data reveal ~ 13° ± 5° counterclockwise rotation since the Calabrian, supporting differential rotation across the Datça Peninsula and linking basin development to progressive opening of the Gökova Basin. Sedimentological evidence documents initial fluvio-lacustrine conditions, followed by a shallow-marine transgressive phase, with the upper marine deposits now > 100 m above present sea level, implying significant post 0.78 Ma uplift. Uplift and facies associations suggest dynamic topography and slab-edge processes associated with STEP faulting along the Pliny-Strabo Trenches controlled the evolution of the basin. Our results provide the most precise chronological framework to date for the Datça Graben, refine its structural development, and constrain the timing of Gökova Basin opening to post-1 Ma. The integration of magnetostratigraphic, geochronological, and structural datasets sheds light on the understanding of Aegean extensional dynamics and the interplay between regional rotation, uplift, and marine connectivity during the Quaternary.