Late Pleistocene–Holocene sea-level rise and the pattern of coastal karst inundation: records from submerged speleothems along the Eastern Adriatic Coast (Croatia)

Abstract

In order to reconstruct the late Pleistocene–Holocene sea-level rise along the Eastern Adriatic Coast, eight speleothems were collected from three submerged caves along the Croatian coast from depths of −38.5 to −17 m. The marine biogenic overgrowth layer and the youngest and the oldest parts of the speleothems were dated by the 14C method. Their stable isotope ( 13C/ 12C and 18O/ 16O) contents were also measured. From the measured 14C activity of the marine overgrowth and using the model of Alessio et al. (1992, Risultati preliminari relativi alla datazione di speleotemi sommersi nelle fasce costiere del Tirreno centrale. Giornale di Geologia ser. 3 54/2, 165–193), the start of overgrowth (i.e., the time of flooding by seawater) was determined to be 10,185 cal BP at −36 m, 9160 cal BP at −34 m, and 7920 cal BP at −23 m. Our results partially match the sea-level curves reconstructed for adjacent areas (Tyrrhenian Coast and French Mediterranean Coast). However, the start of the marine overgrowth on speleothems in pit caves indicates strong dependence on the steepness of the terrain. On steep, extensively karstified coasts, marine overgrowths on speleothems coincided with the submersion of the speleothems due to the relatively short distance between the pit and the open sea and fast penetration of seawater into the pit. In contrast, marine overgrowths on speleothems in pits in the flat terrains occurred later because speleothem growth ceased due to flooding with fresh groundwater. Later, the fresh water was replaced by seawater due to the greater distance of the inland pits to the former coast.