Early Pleistocene initiation of Simav Graben: Implications for widespread extension and landscape change in West Anatolia

Abstract

The prevailing model of west Anatolian extension posits that the westward extrusion of Anatolia, driven by the Northern and Eastern Anatolian transform faults and slab rollback across the Hellenic Trench, governs ongoing extension from Gökova Graben to the Eskişehir Graben in Western Anatolia. However, data gaps and conflicting datasets constrain our understanding of the most recent phase of extension and the underlying geodynamic processes. To address these uncertainties, we investigated the sediment thickness and chronology of the Simav Graben (NW Anatolia) using microtremor surveys, radiocarbon dating and optically stimulated luminescence (OSL) dating from drill cores. Additionally, we examined the geomorphological characteristics of the graben and identified knickpoints along select rivers. Our findings indicate that the Simav Graben is an early Pleistocene (~1.1 Ma) structure with a maximum sediment thickness of approximately 540 m, accompanied by 900 m of maximum vertical displacement along the main bounding fault. Based on alluvial terraces, we infer an uplift rate of 1.1–1.3 mm/year for the last 85 ka, with an average long-term uplift rate of 0.8 mm/year over the graben's lifespan. Our morphological analysis reveals a series of knickpoints unrelated to lithology, beginning at 1300 m and descending to 800 m on hillslopes inclined toward the Sea of Marmara. The synchronous initiation of the Southern Splay of the Northern Anatolian Fault in the Marmara region and the Simav Graben suggests a causal relationship. We propose that the formation of the Northern Anatolian Fault in southern Marmara during the early Pleistocene triggered widespread extension in western Anatolia. Consequently, the north-flowing river networks, except for those associated with the Simav Graben, experienced regional incision.