Advanced luminescence dating of the Karapürçek formation reveals middle pleistocene tectonic reorganization of the North Anatolian Fault Zone

This study establishes the first numerical age constraints for the Karapürçek Formation in northwestern Anatolia, Türkiye, using thermally assisted optically stimulated luminescence (TA-OSL) dating. This formation represents the sedimentary fill of a former pull-apart basin and thus records a critical phase in the evolution of the North Anatolian Fault Zone (NAFZ). Four luminescence samples from a 200-meter-thick section yielded ages ranging from ~ 724 ka to ~ 540 ka, constraining deposition of the formation's upper sections to the Middle Pleistocene (Chibanian Stage). The reliability of these Middle Pleistocene ages is underpinned by a detailed signal analysis. This analysis confirms the TA-OSL signal is highly reproducible and exhibits a strong dosimetric response, validating the technique for this challenging geological context. The resulting age-depth model reveals a consistent apparent sedimentation rate of 0.94 mm/year, interpreted as a direct record of steady tectonic subsidence driven by transtensional faulting. Integrating these new ages with the formation's total estimated thickness (1500-1800 m) allows its full depositional lifespan to be constrained from approximately 2.0 to 0.4 Ma. The cessation of deposition is therefore extrapolated to ~ 400 ka, a timing interpreted to mark a major tectonic reorganization. At this point, strain was localized from the older Karapürçek Fault onto the currently active Sapanca-Akyazı segment of the NAFZ, signifying the extinction of the ancestral pull-apart basin. By providing the first complete, multi-million-year timeline for this basin's initiation, evolution, and extinction, this study offers a new quantitative benchmark for understanding the maturation of continental transform faults and for refining long-term seismic hazard models.