Beachrock formation influenced by co-seismic deformation and relative sea-level changes during the Holocene near the Gulf of Saros, Türkiye (NE Aegean Sea)

This study presents the discovery and detailed analysis of the first confirmed beachrock occurrence on the northern coast of the Gelibolu (Gallipoli) Peninsula in the Gulf of Saros, Northeastern Aegean Sea. Despite the dynamic sandy beaches and rugged coastlines along the southern shores of the gulf, clear evidence of historical co-seismic deformation is preserved in both exposed and submerged beachrock formations. The sedimentary fabric and structural characteristics of these deposits provide critical insights into Late Holocene coastal evolution, including relative sea-level (RSL) fluctuations and tectonic activity. By integrating UAV-based aerial mapping, petrographic and multianalytical microspectroscopic techniques, and radiocarbon dating, this study reconstructs distinct phases of shoreline development shaped by both gradual uplift and episodic seismic events. Radiometric dating of undeformed beachrock indicates ages between 1.1 and 13.6 cal. ka BP, whereas younger, seaward-tilted deposits date to 385 cal. a BP, which is consistent with historical records of the AD 1756 earthquake. After correcting for the local uplift rate (0.76 mm a⁻¹), the data reveal that the RSL decreases by around −0.30 m, aligning with regional Holocene sea-level trends and reinforcing the tectonic context of the Gelibolu Peninsula within a transform-dominated setting. UAV mapping also revealed fracture patterns orthogonal to the North Anatolian Fault (NAF) stress field, supporting links to past seismic events, including the AD 1766 doublet. This study highlights the value of beachrocks as precise geological archives of coastal deformation and sea-level change. Their structural and chronological characteristics refine regional palaeoseismic models and offer a valuable framework for interpreting older or undocumented seismic events along the NAF in the Northeastern Aegean.