The Early Holocene palaeoenvironment of Ounjougou (Mali): Phytoliths in a multiproxy context

Abstract

The site complex Ounjougou on the Dogon Plateau (Mali) comprises sediments up to 100,000 years old with numerous Pleistocene and Holocene sequences. The site Ravin de la Mouche (11.4–10.2 ka) is of special archaeological significance because in its Early Holocene deposits, pottery sherds have been found which are among the oldest in Africa. For a better understanding of the environmental conditions which might have contributed to the innovation of pottery making, a multi-proxy approach was applied to the sediments of Ravin de la Mouche, including phytoliths, pollen, palynofacies, micromorphology and charcoal. The multi-proxy approach also allows reconstructing the complex taphonomy of the site. In our phytolith study, we applied a combination of the general and the indices approaches. We recorded a maximum of morphotypes and used the summarized data for a calculation of the indices D:P, Ic, and Iph, in comparison with modern surface samples and data from other African phytolith studies. With the general approach, a number of morphotypes could be detected which are useful in describing the Late Pleistocene and the Early Holocene vegetation. Phytoliths were extracted from the Pleistocene base and the early Holocene layers HA1, HA2 and HA3. The Pleistocene sediment samples, with an age of ca. 30–40 ka BP, have no grass short cell phytoliths (GSCP) and their composition is difficult to interpret. HA1 is a coarse fluvial deposit with mainly redeposited phytoliths of Pleistocene origin. The palaeosoil in HA2 contains phytolith assemblages developed in situ from a terrestrial plant cover. The vegetation was an open tropical grassland and a gallery forest with palms and Marantaceae. Annuals from the grass subfamilies Chloridoideae and Panicoideae, probably with a low biomass production, dominated the grassland. This might explain the insignificant role of fire, as indicated by the very low number of micro-charcoals. HA3 results from a rhythmic deposition of alluvial sediments, pointing to pronounced seasonality of rainfall and discharge. It contains pollen, charcoal, and phytolith assemblages with a similar composition as in HA2. The Early Holocene annual grassland on the Dogon Plateau probably harboured a high number of species from the grass subfamily Panicoideae with edible grains. We suggest that the massive expansion of useful Panicoid grasses during the Early Holocene triggered the development of important cultural innovations, mainly pottery production. Cooking wild cereal grains in a ceramic container would have enabled a very effective exploitation of the vast Sahelo–Sudanian grasslands, which remained to be successful until modern times.