The Early Paleozoic succession of the Istanbul Zone begins with fine-grained, laminated subtidal–marine sediments containing glauconite and shallows upward into fluvial–deltaic coarse clastics. This regressive succession, continuously deposited until the Mid-Silurian transgressive phase, reaches ~3500 m in thickness. Detrital zircon U–Pb geochronology (n = 513) demonstrates that deposition did not commence in the Cambrian/Precambrian but in the Ordovician, with fluvial–deltaic sedimentation of the Kurtköy Formation beginning in the Late Ordovician and continuing into the Early Silurian (Llandoverian). Whole-rock geochemistry (major and trace element discriminants such as DF1–DF2, SiO₂–Al₂O₃/TiO₂, Th/Sc–Zr/Sc, Co/Th–La/Sc) indicates that sedimentation was dominated by felsic continental crustal sources, with subordinate mafic input. Samples from the Kurtköy Formation further record back-arc/rift influence in tectonic discrimination diagrams. Provenance signals are characterized by strong Pan-African/Cadomian (750–550 Ma) contributions, along with limited Mesoproterozoic, Paleoproterozoic, and rare Archaean zircons, all pointing to a Gondwanan affinity. Paleotectonically, the succession reflects an active continental margin–arc setting during the Ordovician, with sedimentation continuing from Mid-Silurian onwards under passive margin conditions during the transgressive phase. Taken together, the chronological and geochemical data suggest that the Istanbul Zone represents an active margin basin along the northern Gondwana margin, later positioned along the easternmost part of the Armorican domains within the Galatian superterrane with the opening of the Paleo-Tethys, and ultimately accreted to Laurussia during the Variscan orogeny.