Tracking shoreline erosion of “at risk” coastal archaeology: the example of ancient Siraf (Iran, Persian Gulf)

International audienceSuccessful heritage management requires a robust comprehension of the threats facing archaeological sites, at both current and future timescales. Siraf, on the Persian Gulf of Iran, is a site of national and international importance whose history stretches back to the Sassanid period (224-652 AD). In the present context of global change (drought and relative sea-level rise) and anthropogenic impacts (coastal artificialization and reduced sediment supply), the city's waterfront archaeology is undergoing significant erosion. Nonetheless, at present, the processes leading to the loss of Siraf's in situ archaeological remains are still poorly understood, including the rates, timing and drivers of coastal erosion. Here we use Landsat images to monitor shoreline changes along the Siraf coastline between 1973 and 2016. We spatially quantify the causes and impacts of surface changes along 244 transects. The results demonstrate that coastal erosion is responsible for widespread and archaeologically significant damage, with 48% of the studied transects showing erosion during the period 1973-2016. We elucidate significant temporal variations in the data and, most notably, demonstrate that continued drought since the early 2000s has impacted upon sediment supply to coastal areas, severely accentuating erosion. For instance, between 2003 and 2016, 70% of transects recorded shoreline retreat with worrying implications for the waterfront archaeology of Siraf. These quantitative results provide invaluable spatial information regarding the causes and impacts of erosion upon Siraf's waterfront heritage, in addition to furnishing a template for the protection of the city's internationally important cultural heritage

Late Holocene relative sea‐level fluctuations and crustal mobility at Bataneh (Najirum) archaeological site, Persian Gulf, Iran

International audienceThe impacts of relative sea‐level (RSL) variations and crust mobility on the development of ancient harbours in the northern Persian Gulf are poorly understood. Many unanswered questions remain with regard to the main reasons for a shift in the location of the most important ancient harbours in the northern part of the Persian Gulf coastal since 50 BC. Furthermore, some important early Islamic harbours, such as Siraf, have ancient city quarters that are today below the present sea level. The aim of this study is to evaluate the relationship between halokinesis and RSL changes using geophysical models and multidisciplinary geoarchaeological methods at the ancient Sassanid–Islamic site of Bataneh (presently known as Najirum) located at the foothill of an active Darang salt diapir. The results reveal that after the mid‐Holocene highstand, RSL regression was not continuous. The studied facies have recorded three RSL oscillations. The oscillations are correlated with the eustatic sea‐level position. During the first lowstand, important Sassanid harbours shifted from Rishar to Apologus. The second lowstand is consistent with the transition of maritime trade from Apologus to Siraf, during the Abbasid dynasty. Uplift of the Bataneh coastal zone exposed the city to risks from flooding and fluvial debris flows. With a modification of the local watershed, runoff water originating from the salt anticlinal was controlled and used for the extraction of gypsum in evaporation ponds. The economic expansion of Siraf led to Bataneh being abandoned with a shift in trade to Kish Islan

Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf

Historical texts and archaeological studies attest to the maritime and trade importance of the Persian Gulf since the Sassanid Empires. Nonetheless, there is a paucity of data regarding ancient navigation and the reasons for a shift in maritime trade from the western (e.g. Shatt-al-Arab) to eastern (Siraf) Persian Gulf by the Abbasid dynasty. For some scholars, Siraf was occupied between 360 and 977 CE, after which time an earthquake en- trained the demise of the city. However, it is unclear when Siraf was founded and how natural navigation conditions changed for ocean-going vessels in harbours of the NW Persian Gulf. To address this knowledge gap, we here present new geoarchaeological data from Siraf. Two anthropogenic facies were detected in drilled cores. They suggest that Siraf dates back to 2 BC-317 CE. After a hiatus, a second occupation phase began during the reign of Shapur II. Relative Sea-Level (RSL) fluctuations, climate change and Persian Gulf bathymetry all affected the possible nautical accessibility of this ancient Persian harbour. A fall in RSL, leading to a shortening of navigable water columns and amplified summer-time Shamal wind from 550 CE onwards possibly led to a loss in the importance of Shatt-al-Arab and other ports in the western Persian Gulf. It appears to have made Siraf the best alternative for seafarers. According to the wind regimes, the best time for arrival and departure from Siraf was August and October, respectively. 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 CE