Post-Roman sea-level changes on Pag Island (Adriatic Sea): Dating Croatia's “enigmatic” coastal notch?

Abstract

The presence of a regional-wide notch (45 to 115cm below present biological mean sea level [BMSL]) along the Adriatic coast of Croatia, at a string of sites between Zadar and Rijeka, provides evidence for a rapid but poorly constrained subsidence event(s) after Roman times. For more than a century, this geomorphological tidal level indicator has attracted rich scientific debate but many unresolved questions remain. In this paper, we present new results from Caska Bay (Pag Island) looking at notch morphology and Holocene salt-marsh stratigraphy to constrain the chronology of this crustal deformation on Pag Island. The typical salt-marsh stratigraphy comprises low to high salt-marsh muds interjected by an unconformable marine layer (which lies between −50 and −100cm BMSL) consistent with an abrupt transgression. The palaeoecological record shows an abrupt shift in assemblages across the salt-marsh mud–sand sediment contact translating abrupt coastal changes. Geochronological data constrain this event to around 1000 to 1200cal. AD. The altitude of the layer is coeval with the submerged notch attested on limestone cliffs around the bay. The U-shape of the notch profile, coupled with the sharp palaecological contacts and submerged Roman pier, implies that sea-level rise was episodic and not gradual as suggested by regional numerical models. Together, our findings shed new light on the chronology of the “enigmatic” Croatian notch on the island of Pag, and highlight the need to couple geomorphological studies of rocky coasts with high-resolution sediment records.