From section to landscape(s): reconstructions of environmental and landscape changes for the past 8000 years around the site of Wakarida (Ethiopia) using chronostratigraphy

Abstract

In Northern Tigray (Ethiopia), the combined presence in the valley bottoms of sedimentary fills several meters thick and of archaeological remains of human settlements (homes, camps) raises the question of the socio-environmental processes at the origin of these deposits and their interactions with human populations. However, in certain (national, legislative) contexts, it can be difficult to apply very advanced techniques or to perform a large number of analyses. This paper shows that a chronostratigraphic approach based on laser granulometry, loss on ignition and radiocarbon dating provides satisfactory answers to the main geoarchaeological questions. Our specific objective was to reconstruct the landscape and environmental changes in the region around the Wakarida archaeological site, based on the sedimentary deposits in the valley bottoms. These deposits are now cultivated by the inhabitants, thanks to the construction of agricultural terraces in the 20th century. Archaeological excavations unearthed an urban settlement at Wakarida which dates from the classical Aksumite (150–400/450 AD) and post-Aksumite (800/850 AD) periods, and traces of earlier archaeological occupations (pre- and proto-Aksumite periods, 800–50 BC) in the study area. These remains raise questions about the influence of societies on their environment. A method based on a combination of fieldwork, sedimentological analyses and dating was used to answer these questions. This chronostratigraphic study is partially based on the identification of chronological inversions, revealing ablation and depositional phases in the sedimentary cascades, which have to be taken into account to understand the evolution of the site. We identified several phases in the establishment of the present-day landscape around the Wakarida site. During the Northgrippian (Early Holocene), the valleys were progressively filled by low-energy alluvial and/or colluvial processes. During the Meghalayan (Middle Holocene), ablation processes alternated with depositions resulting from climatic processes and possible anthropogenic influences. From the 1st millennium BC, the impact of the population on its environment (deforestation) has resulted in chronological inversions in the deposits, particularly around the 14th and 17th centuries AD.