Late Holocene landscape reconstruction of the lower ‘Ōpūnohu Valley, Moʻorea Island (Society Islands, South Pacific) and its geoarchaeological implications

Abstract

A multidisciplinary study was conducted in the high volcanic island of Moʻorea (South Pacific, French Polynesia) in order to reconstruct its long-term environmental evolution together with its history of human occupation. The ‘Ōpūnohu Valley, in particular, records one of the longest and best documented human histories of the island dating from the first Polynesian (Māʻohi) occupation, from roughly the 11th to the 18th Cent. CE. In order to reconstruct past landscape dynamics that include both the depositional history of the sediments and the shoreline mobility, we have studied six sedimentary profiles from the foothills and from the modern coastal floodplain. Laboratory work includes loss on ignition measurements, laser granulometry analyses and pollen/NPP identification. Chronostratigraphy was based on a series of five radiocarbon datings performed on charcoals, organic sediment, and coral debris. Palaeoenvironmental results reveal two major phases of detrital input related to deforestation (fires) and changes in land use, first during the Māʻohi period, and secondly at the onset of the European period. The substantial delivery of these fine-grained sediments into ‘Ōpūnohu Bay has contributed to the formation of a delta since the onset of the 2nd millennium CE. Our results bring to light the contribution of anthropogenic actions and natural factors to explain the specific landscape evolution of the ‘Ōpūnohu coastal plain since the beginning of human settlement on the island. Finally, our work is of archaeological interest since it helps to determine primary settlement of the Māʻohi people in the context of a rapidly shifting shoreline.