Environmental study of the archaeological site of Bumiayu (South Sumatra, Indonesia)
Since March 2020, the Franco-Indonesian archaeological mission in South Sumatra (Indonesia), directed by Véronique Degroot (archaeologist, EFEO Jakarta) and funded by the DHARMA project (ERC n°809994), includes an environmental component led by Yohan Chabot (postdoctoral fellow geomorphologist, EFEO Paris).
A. The Archaeological context:
The archaeological mission in South Sumatra focuses on the site of Bumiayu. So far, excavations revealed about fifteen remains of ancient brick structures related to Hindu religious activity. Traces of settlements, such as Chinese ceramics, allow to date the occupation of the site between the 8th and 14th centuries CE. These discoveries are interesting because from the 7th to the 11th century, South Sumatra was an international Buddhist centre under the authority of Śrīvijaya. In addition to this particularity, the environmental context of the site also raises questions. Usually, the Śrīvijaya sites are established at strategic places for the control of river traffic – at the confluences and mouths of rivers. Bumiayu seems to be an exception as nowadays the site is located in a meander of the Lematang River, in an alluvial plain flooded during the rainy season. This harsh environment led to the partial disappearance of the remains of the site, swept away by the Lematang and its changing meanders.
B. The scientific purpose:
The main objective is to understand the past landscape dynamics of Bumiayu at the interface of human societies and natural forcings in order to reconstruct the paleogeography and environmental changes that affected it before, during and after its occupation.
C. Two main questions drive this study:
How has the Lematang River changed over time and what impact has active fluvial dynamic had on the permeance of the habitat?
The disappearance of part of the remains of Bumiayu, swept away by the river, raises questions about its evolution and its interaction with human occupation. The paleomeanders preserved in the present landscape attest to the high mobility of the river. This mobility raises questions about the flooding risks incurred by the site. Did this risk already exist at the time of the initial occupation of the site – in this case, what strategies have societies adopted to adapt in a flooded area? – or, did this risk appeared later with the evolution of the natural environment – which may explain the abandonment of the site?
How has the vegetation changed as a result of natural and human factors?
Active fluvial dynamic raises questions about the landscape changes it may have brought about, as well as human occupation. How has the vegetation evolved and what were the ecological dynamics? Has the site environment been exploited (land clearing, slash-and-burn, cultivation)? What was the subsidence economy of the inhabitants of Bumiayu?
D. The scientific method combines two approaches:
1/ First, a geomorphological approach.
It is the main focus of the study. It aims to define the nature of the deposits, their thickness and their chronology in order to understand the hydro-sedimentary dynamics. Several corings will be carried out in the Lematang paleomeanders in Bumiayu and around the site. Sediment samples will be taken from the sediment cores for analysis (grain size, organic matter content, fire signal, magnetic susceptibility). This approach will support paleographic (evolution of the Lematang, succession of paleomeanders and reconstruction of the landscapes of the Bumiayu floodplain); environmental (dynamics of aquatic and wetland environments, fluctuations in the level of water tables – seasonal, decadal, secular) and chronological interpretations.
2/ A bio-indicator approach, based on the analysis of phytoliths preserved in the Bumiayu deposits, will complete the geomorphological study.
This aim is to reconstruct the evolution of the vegetation and to define the human activities impact (e.g. land clearing, cultivations) on the environment. Phytoliths are micrometric mineral particles of plant cells. They provide information about past vegetation, resources and humans practices. Data acquisition will be based on two types of sampling:
- A modern soil sampling in the main plant formations representative of the local and regional phytogeographical context. The aim is to establish a modern referential and to test the potential of phytoliths for the landscape reconstruction.
- A sampling in the sedimentary deposits of Bumiayu to identify changes in vegetation cover and markers of agricultural practices. Data interpretation will be based on analogues of the modern referential.
[For now, this research has not yet begun. The first mission planned for spring 2020 has been cancelled due to the covid-19 pandemic. Missions should take place in 2021 and 2022]