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

Geoscience is a very useful tool for approaching the relationships between societies and their environment. However, it is not always possible to apply very advanced techniques or to perform a large number of analyses. This paper aims to show that chronostratigraphic studies can provide satisfying answers to the main geoarchaeological questions, “only” using sedimentological, stratigraphic and chronological analyses. The objective here is to move from the study of stratigraphic sections, uncovered in valley bottoms filled by sedimentary deposits, to the reconstruction of landscape and environmental changes, in connection with the archaeological site of Wakarida (northern Tigray, Ethiopia). The actual landscape around Wakarida is made of steeply sloping valleys, filled with accumulations of sediments several meters thick. These deposits are cultivated by the inhabitants thanks to the building of agricultural terraces. Archaeological excavations have uncovered an urban settlement in Wakarida, dating between the classical Aksumite (150-400/450 CE) and the post-Aksumite periods (800/850 CE), and more ancient (pre- and proto-Aksumite periods) structures in the area under survey. Such structures raise the question of the interactions of the populations with their environment through time. More precisely, they question their role in the deposition of the sediments. To tackle these questions, a method based on a combination of field work, sedimentological analyses and dating has been employed. Such a chronostratigraphic study made it possible to identify several phases in the establishment of the current landscapes around the Wakarida site. During Early Holocene, valleys were gradually filled by alluvial and/or colluvial processes of low energy. During Middle Holocene, ablation processes alternated with deposition, showing the effects of climatic and possible anthropogenic processes. From the 1st millennium BCE onwards, the impact of population on their environment is visible, but especially around the 14th – 17th centuries. An important part of these conclusions is based on the attention given to chronological inversions and the fact that these dates, "false" at first glance, reveal ablation and deposition phases within sedimentary cascades. It therefore seems important, from a methodological point of view, not to reject these dates a priori, but to consider them by giving them their full place in the chronostratigraphic reflection.