Silting-up of the Frejus ancient harbour (Forum Julii, France) during the past 2000 years: A two-phase model of palaeoenvironmental change

The ancient harbour of Frejus, located in a Holocene ria, has been the subject of a research program in archaeology and, notably with regards to the sedimentary environment at its foundation. A core was extracted in the middle of the basin of Frejus harbour. The objective is to understand the paleogeographical evolution of the pre-harbour and Roman harbour environments. The sedimentological and biostratigraphical proxies enabled us to: (1) confirm Texier's (1849) hypothesis in which the pre-harbour environment comprised a marine bay blocked by an artificial quay (Gebara and Morhange, 2010). Excoffon et al., 2006 and Devillers et al., 2007, demonstrate the presence of a rocky coast (butte Saint-Antoine), at the time of the harbour's foundation, which it has been progressively transformed into a sandy coast due to the sedimentary input of Argens delta. This study permitted: (2) to confirm the date of foundation of Frejus' harbor: and (3) to show different phases of protection. Indeed, the harbour fades attests to a euryhaline lagoon (B1 and B3) which was gradually transformed into a freshwater lake (B4) due to the progradation of the Argens. Low sedimentation rates (ca. 0.5 mm/year), between the end of the last century BC until seventh century AD is consistent with the dredging of the harbour basin. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.