Palaeogeographical and palaeoenvironmental reconstruction of the Medjerda delta (Tunisia) during the Holocene

Résumé En

The progradation of the Medjerda delta has been the subject of many studies since the 19th century. Thescale and the rapidity of this phenomenon interested researchers in various fields early on, such asgeomorphology, geology, palaeogeography, history, archaeology, or geoarchaeology. Indeed, the deltaprograded by around 10 km over 3 millennia. At the time of its foundation supposedly at the end of the12th century BC, the Phoenician city of Utica was located on a promontory bathed by the sea, but thesediments carried by the Medjerda progressively sealed the bay, leaving the tip of the Utica promontorynow 10 km inland. This area is therefore an exception to the general pattern along the Tunisian coast,since as over the same period everywhere else there is a regression of the coastline, owing to a sea levelrise of several decimeters. Based on multi-proxy analyses of two coring transects, this paper aims toreconstruct the palaeoenvironments and the palaeogeography of the Medjerda delta’s progradation sincethe mid-Holocene, some aspects of which are described in ancient sources. The results highlight inparticular an episode of high-intensity flooding around the 4th century AD, which is consistent withepisodes of high floods and an increase in sedimentation rates recorded in the watershed at the end ofthe Roman period. The gradual abandonment of the city of Utica can certainly be related to the activity ofthe Medjerda River, but our results show that it is because of an increase of fluvial sediment contributionin connection with an erosive crisis in the headwaters, and not because of the change of course of theriver, which had occurred long before.