Soutenance de thèse de Majid POURKERMAN

Le golfe Persique a été une lieu stratégique pour l’empire Perse puis le Caliphat arabe. L’empire sassanide était interessé de controler le golfe Persique afin de dominer les échanges commerciaux. A cette époque, Rishar (Rev Ardeshir) et Apologus étaient deux ports majeurs du nord-ouest du golfe Persique. Apologus était un port fluvial à l’embouchure du Shatt-al-Arab alors que Rishar était situé sur la péninsule de Bushehr. L’activité commerciale d’Apologus ne sera dépassée par Busher que depuis environ 1700 ans, bien que le commerce maritime continue à Apologus entre la période omeyyade et le début de la période abbasside (vers 1300-1200 BP). Au début de la période abbasside, Apologus se développe à nouveau jusque vers 1200 BP, du fait de la proximité de Bagdad, capitale de l’empire. Les publications décrivent une transfert soudain de l’activité des ports du nord-ouest en direction de la partie centrale du golfe Persique (d’Apologus vers Siraf) vers 1200-1100 BP. Siraf a été un des ports majeurs du golfe Persique Durant toute l’époque médiévale. Au 11° siècle de l’ère chrétienne, Siraf decline au profit de l’île de Kish. Cette mobilité géographique vers l’ouest, d’Apologus vers Rishar, Siraf, puis Kish s’est effectuée sous les même régimes politiques. Cette migration est complexe à expliquer. Pour répondre à cette question, nous avons étudié les impacts des paleo-environnements sur la navigation et la localisation des ports dans l’Antiquité. Des études géoarchéologiques multi-disciplinaires, ont été effectuées à Siraf et à Najirum. Les résultats de ces travaux montrent que certains parametres physiques, comme le vent Shamal (vers 1300 BP), La morphologie littorale, les courants de surface, la mobilité relative du niveau marin, la géomorphologie du delta du Shatt-al-Arab et la néo-tectonique, ont joué un role dans la géographie des voies navigables et l’accessibilité aux ports médiévaux. La courbe de variation relative du niveau marin présente 3 oscillations. qui sont en correlation positive avec un accroissement de la hauteur de la colonne d’eau et une activité tectonique salifère dans la partie centrale du golfe Persique

The Persian Gulf is located south of Iran and it was an important theatre for the Persian Empires and Arab Caliphas. The present geomorphology of the Persian Gulf is controlled by both plate and salt tectonics. The impacts of relative sea-level (RSL) variations, climate changes, basin morphology and coastal uplift on the development of ancient harbours and navigation in the northern Persian Gulf are still unknown. Many questions remain unanswered regarding the changes in the location of important harbours by the Sassanids (Rishar to Apologus in the northwest) and Abbasid Calipha (Apologus to Siraf and Najirum at central), in addition to the impacts of climate changes on maritime navigation in the Persian Gulf. Furthermore, there is a paucity of data regarding the interaction between regional sea-level rise and salt tectonics on the RSL oscillations and coastal uplift in the northern Persian Gulf. In this thesis, we employed a multidisciplinary methodology to shed light on the history of maritime activities in the Persian Gulf, coastal dynamics and the reconstruction of RSL changes during the mid to late Holocene. The principal aim of this study was to evaluate the risk of natural and anthropogenic processes on waterfront archaeological sites. The results demonstrate that RSL in the Persian Gulf is controlled by both regional sea-level changes and local salt tectonics. After the mid-Holocene RSL rise, two lowstands are recorded. 1- The first lowstand (1.7-1.5 kyr B.P.) was concurrent with increasing flow in the Shatt-al-Arab and a deeper fluvial water column. It led to a shortening of navigable water columns in shallow coastal areas and a shift in important Sassanian harbours from the coastal peninsula of Rishar to the fluvial context of Apologus. 2- The second RSL fall coincided with a reduction in the Shatt-at-Arab water column and the onset of the summer NW Shamal wind (1.4 kyr B.P.). The most significant impact of the summer Shamal wind was on Ras-e-Motaf and the second RSL fall led to the navigable water column becoming too shallow during low-tide in the Shatt-al-Arab estuary. Therefore, the risks of sinking and trapping for ocean-going vessels were increased. These environmental factors appear to have made Siraf the best alternative for seafarers. The last lowstand was concurrent with rapid coastal uplift at Bataneh (Najirum), following salt injection into the Darang salt dome. It caused a coastal uplift of ca. +3.7 m. With decreasing water column, RSL oscillation intervals were increased. RSL rise and increasing coastal erosion during the winter-time Shamal winds led to the degradation of harbour potentialities and was possibly at the origin of economic decline and poorly adapted harbour works at Siraf during a 150-year period between 850 and 1000 kyr B.P. The economic dependence of Bataneh on Siraf, led to Bataneh being abandoned with a shift in trade to Kish Island at around 1 kyr B.P. Shoreline movements of Siraf’s coastline were evaluated along 244 transects during the period 1973-2006. Since the 2000s, a decreasing sediment budget is the result of drought, increasing anthropogenic activities in the coastal zone and local watershed modifications. 70% of the studied transects recorded erosion with worrying implications for the waterfront archaeological remains. It is suggested that coastal erosion is responsible for widespread archaeological damage to Siraf’s waterfront. Meanwhile, oil and gas fields have led to the expansion of several petrochemical factories along the coast. They have had direct and indirect impacts on the destruction of ancient sites. For instance, 90% of the ancient site of Bataneh has been destroyed during last 20 years. Further geoarchaeological studies are required at waterfront sites of the Persian Gulf because many sites are being quickly destroyed by modern developments, present RSL rise and coastal erosion.