Glycymeris shell accumulations as indicators of recent sea-level changes and high-energy events in Cadiz Bay (SW Spain)

Abstract

Recent climatic and sea-level changes have significantly modified coastal areas, and caused the morphological evolution of littoral environments. Such is the case in Cadiz Bay (SW Spain), where important changes have taken place from the Late Holocene to the present-day, and which have not yet been sufficiently established. In this sense, some sedimentary indicators such as the Glycymeris shell deposits which can be found interstratified in recent coastal sand banks could shed new light on this issue. Three questions are addressed in this work. Firstly, the age of these shell deposits, secondly, what is the depositional mechanism responsible for these shelly accumulations, and finally, what relationship can be established regarding recent sea-level changes. Sample ages indicate that the shells are older than 1000 years BP, while the facies indicate high-energy flows. As depositional mechanisms, tides and waves seem insufficient in order to reach the upper shelly deposits, for which a more energetic agent would be necessary, such as tsunami waves, which is feasible given that the zone is located in a tectonically active area, where historical tsunamis have been recorded. With respect to the relationship with a possible recent sea-level rise, this could be a better explanation, since marine agents would be able to reach the necessary height.