Rhodolith beds along the southeastern Mediterranean inner shelf: Implications for past depositional environments

The inner structure of multitaxonomic boxwork rhodoliths from a seabed located off of the Northern Israeli coast was explored as a tool to understand past depositional environments of the shallow littoral zone. Studied rhodoliths consist of superimposed, successive growth stages formed by different encrusting biota. The types of growth stages include fruticose encrusting coralline algae layers, and layers of serpulid tubes, grainstone or encrusting coralline algae. Carbon dating of radial sections cut from along the growth axis of two large rhodoliths (~8 cm radial sections) suggests that the transition between these layers occurred at the same time, and that layers dominated by different phyla have significantly different growth rates, ≥0.3 ̶ ~0.8 mm yr⁻¹ for the serpulid layers and 0.1–0.4 mm yr⁻¹ for the coralline algae stages. Layers of sediment grains between some of the growth stages suggest that the successions occurred during high turbidity periods in the surrounding water, possibly induced by heavy rain or storm events. Radio-carbon dating of the largest rhodolith samples shows a record of such environmental influence in the area dating back 366 ± 57 years cal. B.P. Studies on boxwork rhodolith growth stages are a potential archive of past depositional environments in the shallow littoral zone.