Tracking Mid- to Late Holocene depositional environments by applying sedimentological, palaeontological and geochemical proxies, Amvrakikos coastal lagoon sediments, Western Greece, Mediterranean Sea

This study presents sedimentological, palaeontological, geochemical, mineralogical, and organic petrography data from a 30 m deep core representing a Mid- to Late Holocene lagoonal depositional environment, of a coastal area of Amvrakikos Gulf, Western Greece. Three horizons were dated using 14C. The sedimentological, palaeontological and geochemical interpretations of the lagoonal sediments reveal three major lithological units deposited between around 5200 and 1600 BP. The upper lithological unit extended to a depth of 11.20 m, the middle from 11.20 to 21.30 m, and the lower one from 21.30 to 30.00 m. A mean rate of sedimentation of 5.7 mm/y and a maximum rate of 12.6 mm/y were estimated. The mineralogical analysis and the magnetic susceptibility of the core points to a constant sediment – source supply. The Mid- to Late Holocene depositional environment mainly reflects inundation by the braid plain of the Arachthos and secondarily by the Louros River. The reconstruction of the depositional environments corresponds to a shallow marine and deltaic brackish lagoon and specifically to an environment proximal to river supply. The high rates of sedimentation, as well as the interpretation of depositional environments, indicate that the coastal sedimentological processes during the Mid- to Late Holocene were mainly controlled by the progradation of river deltas. Moreover, the geochemical proxies, the recovered molluscs and the microfauna, as well as the organic petrography analyses indicate periods of dysoxic and hypoxic conditions. These Holocene dysoxic and hypoxic events indicate that the recent dystrophic crises in the Amvrakikos Gulf are not only the result of human activities but also the contribution of natural processes.