Meghalayan environmental evolution of the Thapsus coast (Tunisia) as inferred from sedimentological and micropaleontological proxies

Abstract. Thapsus was one of the Roman Empire's largest harbors and is situated next to an easily defended promontory on Tunisia's coast in northern Africa. It was provided with a huge stone and cement breakwater mole that extended almost 1 km into the sea. We examined sedimentological and micropaleontological proxies from 14C-dated core material and shifts in microfauna and macrofauna community structure to infer patterns of sediment dynamics and the chronology of events that shaped the coastal evolution in the Dzira Lagoon at Thapsus over the past 4000 years. The sedimentological and faunal record of environmental changes reflect a sequence of events that display a transition from an open to a semi-closed lagoon environment. At around 4070 cal yr BP and again between 2079 and 1280 cal yr BP, the data reveal two transgressive events and a deposition of sandy sediments in a largely open marine lagoon environment. The transgressive sands overlay marine carbonate sandstones that are upper Pleistocene in age. A gradual closure of the lagoon from 1280 cal yr BP until today is indicated by decreasing species richness values, lower abundances of typical marine taxa, and increasing percent abundances of fine-grained sediments. The environmental transition from an open to a closed lagoon setting was also favored by the construction of an extensive harbor breakwater mole, changes in longshore current drift patterns, and the formation of an extensive sand spit.