Geoarchaeology of the ancient city of Utica (Tunisia) and evolution of the palaeoenvironment of the Medjerda delta

Phoenician Utica remains today largely unknown, as is its role in the Phoenician expansion in the western Mediterranean. Aristotle and Pliny the Elder mention Utica as a maritime and port city and estimate its origin around the 11th c. BC. However, in the present state of research, no archaeological evidence is earlier than the 9th c. BC, and the location of the Phoenician and Roman port infrastructures remains unknown. Today, the ancient city is located on a promontory in the heart of the Medjerda delta, 10 km inland. This project proposes an interdisciplinary effort to understand the Medjerda delta landscape changes during the Holocene. It starts from an archaeological problem and proposes the contribution of geoarchaeology to the understanding of the relationship between ancient societies and their environment. The fluvial palaeoenvironments and sedimentary processes are studied through the mechanical extraction of cores (15-20 m deep) to reach the early Holocene. Selected sediment samples are then studied in laboratory, using different and complementary approaches. The location of port infrastructures will bring initial answers to the question of the foundation of the city. The study of river palaeoenvironments of the Medjerda delta during the Holocene aim at a better understanding of the nature of the settlement, as well as the function of the city of Utica over time. This study will also assess the impact of the ancient city on the environment and understand how the city adapted to the mobility of this Mediterranean delta. Furthermore, the analysis of sedimentary processes causing the filling of the harbour basin will lead to speculation about the causes of the abandonment of the structures and more generally the decline of the city in favor of Carthage. It will also examine whether natural or anthropogenic factors have influenced this deltaic progradation over the centuries

Evolution of the Medjerda delta's palaeoenvironment : Evidence of an intense sedimentation event post 10th c. A.D. near the ancient city of Utica (Tunisia)

International audienc

Evolution des paléoenvironnements du delta de la Medjerda

Ce poster présente un projet de réflexion interdisciplinaire visant à comprendre le rythme d’évolution des paysages deltaïques au cours de l’Holocène. Depuis la fin du XXe siècle, la progradation deltaïque de la Medjerda a fait l’objet de nombreuses investigations (e.g. Oueslati, 1995 ; Paskoff et al., 1992). Partant des sources écrites et de données archéologiques, ce phénomène de comblement a également été étudié plus récemment par le biais de la géoarchéologie et d’un système d’information géographique (SIG - Delile et al., 2013). Ces études ont conduit à l’élaboration d’un schéma spatio-temporel des multiples défluviations qu’a connues la Medjerda au cours de son avancée sur la mer. L’étude des paléo-environnements fluviaux et des processus sédimentaires sera réalisée par l’intermédiaire de carottages d’une dizaine de mètres de profondeur, afin d’atteindre les couches correspondant aux environs de la première moitié de l’Holocène. Les échantillons de sédiments sélectionnés seront ensuite étudiés en laboratoire selon différentes approches complémentaires : (1) analyse granulométrique et morphoscopie du quartz : reconstitution des conditions hydrodynamiques ; (2) analyse minéralogique par diffraction des rayons X : identification et estimation de l’abondance des composants sédimentaires détritiques, biologiques et authigènes ; (3) analyse géochimique par spectrométries XRF et ICP-AES : identification des sources sédimentaires et mise en évidence de la contamination anthropique ; (4) analyse palynologique : reconstitution du couvert végétal ; (5) étude des ostracodes : reconstitution des environnements sédimentaires (nature du milieu) ; (6) analyse géochimie isotopique du plomb : identification des sources de pollutions. L’analyse granulométrique renseignera l’hydrodynamisme et précisera les processus impliqués dans les phases successives de dépôts qui caractérisent différents environnements sédimentaires (e.g. Goiran et al. 2014). Elle sera complétée par une série d’analyses sédimentologiques (susceptibilité magnétique, minéralogie, géochimie organique et inorganique) et biologiques (pollens, ostracodes) afin de reconstituer l’évolution des paysages sur les derniers millénaires. Cette reconstitution sera mise en relation avec les changements climatiques au cours de l’Holocène. La combinaison des approches minéralogiques et géochimiques permettra d’identifier l’origine des minéraux argileux, de déterminer leurs régions sources et de mettre en évidence une contamination par les activités humaines. L’influence des facteurs anthropiques sera confirmée par une analyse des isotopes du plomb (e.g., Fagel et al., 2010). Différents traitements statistiques seront appliqués aux résultats de ces analyses dans le but d’affiner leur interprétation. Parallèlement, une série de datations radiocarbone seront réalisées afin de fixer le cadre chrono-stratigraphique des différentes phases d’évolution du delta. La plus-value de ce projet réside dans l’approche pluridisciplinaire, qui visera à proposer une image évolutive des paysages du bassin versant de la Medjerda, et précisera les modalités d’enregistrement sédimentaire en fonction de variables de contrôle que sont le climat et la pression anthropique. Plus globalement, ce projet met l’accent sur l’importance de la connaissance et des enseignements du passé pour comprendre et appréhender les conséquences de l’anthropisation de l’environnement, plus spécifiquement sur les milieux deltaïques

PALEO-DELTA: Palaeoenvironment and geoarchaeology of the Medjerda delta (Tunisia)

Phoenician Utica remains today largely unknown, as is its role in the Phoenician expansion in the western Mediterranean. Aristotle and Pliny the Elder mention Utica as a maritime and port city and estimate its origin around the 11th c. BC. However, in the present state of research, no archaeological evidence is earlier than the 9th c. BC, and the location of the Phoenician and Roman port infrastructures remains unknown. Today, the ancient city is located on a promontory in the heart of the Medjerda delta, 10 km inland. This project proposes an interdisciplinary effort to understand the Medjerda delta landscape changes during the Holocene. It starts from an archaeological problem and proposes the contribution of geoarchaeology to the understanding of the relationship between ancient societies and their environment. The fluvial palaeoenvironments and sedimentary processes are studied through the mechanical extraction of cores (15-20 m deep) to reach the early Holocene. Selected sediment samples are then studied in laboratory, using different and complementary approaches. The location of port infrastructures will bring initial answers to the question of the foundation of the city. The study of river palaeoenvironments of the Medjerda delta during the Holocene aim at a better understanding of the nature of the settlement, as well as the function of the city of Utica over time. This study will also assess the impact of the ancient city on the environment and understand how the city adapted to the mobility of this Mediterranean delta. Furthermore, the analysis of sedimentary processes causing the filling of the harbour basin will lead to speculation about the causes of the abandonment of the structures and more generally the decline of the city in favor of Carthage. It will also examine whether natural or anthropogenic factors have influenced this deltaic progradation over the centuries

Geoarchaeology of the ancient city of Utica (Tunisia) and evolution of the Medjerda delta's palaeoenvironment

The Phoenician Utica remains today largely unknown, as well as the role that the ancient city held in the Phoenician expansion in the western Mediterranean. Aristotle and Pliny the Elder mentioned Utica as a maritime and port city and evaluate its origin around the 11th c. BC.. However, in the present state of research, no archaeological evidence goes back beyond the 7th c. BC.. Today, the ancient port city is located in the heart of the Medjerda delta, 10 km inland. Although the Utica site has been the subject of archaeological excavations since the 19th c., the location of port infrastructures, dating from Phoenician and Roman periods, remains unknown. Based on this observation, our research focuses on two main issues: Where are the port infrastructures of Utica? Why the city, formerly a seaport city, is today located 10 km from the coast? The location and the study of port infrastructures will bring primordial elements of response to the question of the city founding. The study of river paleoenvironments of the Medjerda delta during the Holocene aim to a better understanding of the nature of the settlement, as well as the function of the city of Utica. This study will also assess the impact of the ancient city on the environment and understand how the city has adapted to the mobility of this Mediterranean delta. Furthermore, the study of sedimentary processes causing the filling of the harbour basin will lead to speculate about the causes of the abandonment of the structures and more generally the decline of the city in favor of the city of Carthage. It will also detect if natural or anthropogenic factors have influenced this deltaic progradation over the centuries. This project proposes an interdisciplinary reflection to understand the Medejerda delta landscape changes during the Holocene. It starts from an archaeological problem and proposes the contribution of geoarchaeology to the understanding of the relationship between ancient societies and their environment. A major originality of this project lies in the multidisciplinary approach, which aim to provide an evolutive image of the landscapes of the Medjerda watershed, and to precise the sedimentary record considering control variables such as climate and anthropogenic pressure. The study of fluvial palaeoenvironments and sedimentary processes will be carried out through the mechanical extraction of cores (~10 m deep) to reach the early Holocene. Selected sediment samples will then be studied in laboratory, using different and complementary approaches. Particle size analysis and quartz morphoscopy will help to clarify the processes involved in the successive phases of deposits associated with different sedimentary environments. It will be supplemented by a series of sedimentological (magnetic susceptibility, mineralogy, organic and inorganic geochemistry) and biological analyses (pollen, ostracods) to reconstruct the evolution of the landscape over the last millennia. This reconstruction will be related to climate changes during the Holocene. The combination of mineralogical and geochemical approaches will help to identify the origin of clay minerals to determine their source regions and to highlight contamination by human activities. The influence of anthropogenic factors will be confirmed by analysing lead isotopes. Meanwhile, a series of radiocarbon dating will be conducted to establish the chrono-stratigraphic framework of the different evolution phases of the delta. More generally, this project focuses on the importance of knowledge of the past to understand and grasp the consequences of the human impact on the environment, more specifically on the deltaic environments

Mise en évidence par la luminescence des feldspaths de deux hauts niveaux marins interglaciaires du Pléistocène moyen (MIS 7 et MIS 9) le long de la côte orientale de la Tunisie (Sahel)

La méthode de datation IRSL sur feldspaths alcalins (200-250 μm) est appliquée aux deux unités marines sableuses, dépourvues de Strombes et d’oolithes, de la Formation Douira, unité morphostratigraphique caractéristique du Pléistocène moyen marin du Sahel tunisien. Les âges IRSL de ces deux unités marines, obtenus à El Hajeb, à proximité de la localité type de Douira au Sahel, confirment l’âge pré-tyrrhénien de la Formation Douira. Ils démontrent par ailleurs, pour la première fois, l’existence au sein de cette formation, de deux hauts niveaux marins distincts, corrélatifs des MIS 7 et 9. Ces deux unités marines sableuses sont séparées à El Hajeb, par une surface d’érosion majeure et à Réjiche, par un limon continental pédogénéisé témoignant d’un épisode de bas niveau marin qui pourrait être corrélé au MIS 8. Nous proposons donc ici de subdiviser cette Formation Douira en deux membres, inférieur et supérieur, attribués respectivement aux MIS 9 et 7. Ces deux hauts niveaux marins sont contemporains des hauts niveaux lacustres du sud-ouest tunisien et de Libye ainsi que des sapropèles du bassin méditerranéen.The IRSL dating method is applied to alkali feldspar grains (200-250 μm) from the two sandy marine units of the Douira Formation, a Middle Pleistocene morphostratigraphic marine unit specific to the Tunisian Sahel area. This formation is devoid of Strombus bubonius and ooids. The IRSL ages of both marine units, obtained at El Hajeb, close to the type locality of Douira in the Sahel area, confirm the pre-tyrrhenian age of the Douira Formation. Moreover, they demonstrate, for the first time, the presence of two successive interglacial high sea-level events within the Douira Formation, correlative of MIS 7 and MIS 9. These sandy marine units are separated, at El Hajeb, by a major erosional surface and, at Rejiche, by a continental pedogenised loamy deposit related to a low sea-level event that might be assigned to MIS 8. We therefore suggest herein to subdivide the Douira Formation into two members, a lower and an upper member correlated respectively with MIS 9 and 7. Both high sea-level stands coincide with the development of extensive Middle Pleistocene paleolakes in south-western Tunisia and Libya and the formation of sapropels in the Mediterranean basin

Where is the ancient harbour of Utica ? Geoarchaeology and palaeoenvironment of the Medjerda delta (Tunisia)

Ancient authors mention Utica as a maritime and port city and estimate its origin around the 11th c. BC. However, in the present state of research, no archaeological evidence is earlier than the 9th c. BC, and the location of the Phoenician and Roman port infrastructures remains unknown. Today, the ancient city is located on a promontory in the heart of the Medjerda delta, 10 km inland. This project proposes an interdisciplinary effort to understand the Medjerda delta landscape changes during the Holocene. It starts from an archaeological problem and proposes the contribution of geoarchaeology to the understanding of the relationship between ancient societies and their environment. The fluvial palaeoenvironments and sedimentary processes are studied through the mechanical extraction of cores (15-20 m deep) to reach the early Holocene. Selected sediment samples are then studied in laboratory, using different and complementary approaches. First results permitted to draw an hypothesis of the coastline during Antiquity and to bring out the evidence of an intense sedimentation event post 10th c. BC. The location of port infrastructures will bring initial answers to the question of the foundation of the city. The study of river palaeoenvironments of the Medjerda delta during the Holocene aim at a better understanding of the nature of the settlement, as well as the function of the city of Utica over time. This study will also assess the impact of the ancient city on the environment and understand how the city adapted to the mobility of this Mediterranean delta. Furthermore, the analysis of sedimentary processes causing the filling of the harbour basin will lead to speculation about the causes of the abandonment of the structures and more generally the decline of the city in favor of Carthage. It will also examine whether natural or anthropogenic factors have influenced this deltaic progradation over the centuries

Evolution of the palaeoenvironment of the Medjerda delta (Tunisia) and geoarchaeology of the ancient city of Utica

Phoenician Utica remains today largely unknown, as is its role in the Phoenician expansion in the western Mediterranean. Aristotle and Pliny the Elder mention Utica as a maritime and port city and estimate its origin around the 11th c. BC. However, in the present state of research, no archaeological evidence is earlier than the 9th c. BC, and the location of the Phoenician and Roman port infrastructures remains unknown. Today, the ancient city is located on a promontory in the heart of the Medjerda delta, 10 km inland. This project proposes an interdisciplinary effort to understand the Medjerda delta landscape changes during the Holocene. It starts from an archaeological problem and proposes the contribution of geoarchaeology to the understanding of the relationship between ancient societies and their environment. The fluvial palaeoenvironments and sedimentary processes are studied through the mechanical extraction of cores (15-20 m deep) to reach the early Holocene. Selected sediment samples are then studied in laboratory, using different and complementary approaches. The location of port infrastructures will bring initial answers to the question of the foundation of the city. The study of river palaeoenvironments of the Medjerda delta during the Holocene aim at a better understanding of the nature of the settlement, as well as the function of the city of Utica over time. This study will also assess the impact of the ancient city on the environment and understand how the city adapted to the mobility of this Mediterranean delta. Furthermore, the analysis of sedimentary processes causing the filling of the harbour basin will lead to speculation about the causes of the abandonment of the structures and more generally the decline of the city in favor of Carthage. It will also examine whether natural or anthropogenic factors have influenced this deltaic progradation over the centuries

Geoarchaeology of the Ancient Harbour of Utica in a Deltaic Context (2014 and 2015)

Ancient authors mention Utica as a maritime and port city and estimate its origin around the 11th c. BC. However, in the present state of research, no archaeological evidence is earlier than the 9th c. BC, and the location of the Phoenician and Roman port infrastructures remains unknown. Today, the ancient city is located on a promontory in the heart of the Medjerda delta, 10 km inland. Based on this observation, our geoarchaeological research focuses on two main issues: - Was there a marine environment around the promontory of Utica, which could shelter harbour structures? - Why the city, formerly a seaport city, is today located 10 km from the coast? Can the wadi be solely responsible of such an important sediment accumulation in a few millennia? Have any natural or anthropogenic factors influenced this deltaic progradation over the centuries? First results permitted drawing an hypothesis of the coastline during Antiquity to the effect that the Utica promontory was surrounded by the sea in an earlier era. (1) Effectively, the «North compartment» of the delta was covered by the sea at a given time, which will be determined by the next radiocarbon dating. But the sea still brushed the north side of the promontory during the Roman period, as evidenced by the potsherds found in one of the cores. This deep marine bay could be a potential location for harbour infrastructure prior to clogging of the bay by the sediments carried by the wadi. (2) The «corridor» area, materialised by the promontories of Utica and Kalâat el-Andalous, was also invaded by the sea at one time. The many artifacts found in this core attest the occupation of this area, outside of the maximal extension of the ancient city according to A. Lézine. Dating of the marine units in the two cores will bring essential data: * to establish the chronological framework of the retreat of the coastline and of the clogging of the bay; * to understand the passage of the Medjerda into the «North compartment» by the corridor Utica-Kalâat. The geoarchaeological results corroborate ancient sources. Utica was able to welcome important harbour structures, since the presence of a deep marine environment is attested around the promontory, but these remains are probably 5 m deep under the alluvium of the Wadi Medjerda