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

Abstract

a b s t r a c t a r t i c l e i n f oThe 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 multiproxy 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.

Possible source of ancient carbon in phytolith concentrates from harvested grasses

“…Because phytoliths are normally well preserved in oxidizing environments, their morphological assemblages have been widely used for paleo-environmental reconstructions and archaeological and paleontological research (e.g., Piperno and Becker, 1996;Alexandre et al, 1999;Prebble et al, 2002;Prasad et al, 2005;Bremond et al, 2005Bremond et al, , 2008aPiperno, 2006;Alam et al, 2009;Neumann et al, 2009;Rossouw et al, 2009). In parallel, quantification of phytoliths in plants, soils, and rivers has been used to study the biogeochemical cycle of silica, which itself is coupled to the global C cycle (Blecker et al, 2006;Struyf et al, 2009;Cornelis et al, 2011;Alexandre et al, 2011).…”

Diatom, phytolith, and pollen records from a 10Be/9Be dated lacustrine succession in the Chad basin: Insight on the Miocene–Pliocene paleoenvironmental changes in Central Africa

“…Phytoliths are good indicators to trace the existence of true tropical forest environments in tropical Africa (Fig. 4) (Bremond et al, 2005a;Aleman et al, 2011) but, conversely, they still fail to reconstruct the ligneous cover in tropical savanna environments (Neumann et al, 2009;Novello et al, 2012). As a result, the Bol phytolith data cannot provide much information on the presence/abundance of the ligneous cover in these paleo-savannas.…”

“…9) currently occurring in the Lake Chad basin (Gaston, 1996). Some authors (Neumann et al, 2009;Prasad et al, 2011), however, asserted to have identified a specific bilobate type -"the bilobate type with scoped ends" -which they described as diagnostic of the Ehrhartoideae grass subfamily. The description criteria and classification used in this study were not designed to specifically isolate this bilobate type that may have thus be counted as part of the bilobate types with notched ends (Bi8 type) (see Table 3 for Bi-8 type photograph), which in fact probably include a larger morphological variability than the bilobate type with scoped ends itself.…”

Hydrosedimentary records and Holocene environmental dynamics in the Yamé Valley (Mali, Sudano-Sahelian West Africa)

“…The rainy season contributed to rambling flow with strong competence in a wide sandy gravel bed while the dry season led to decantation deposits in permanent pools as shown by the absence of desiccation evidence at the top of the fine deposits attributable to the dry season. Moreover, for the first time in the sedimentation, the abundance and nature of organic material evidences the importance of the vegetal cover in the valley base (riverain) and slopes (Eichhorn and Neumann, 2007;Neumann et al, 2009). This indicates the transition to a calmer river system that can be explained by the reconquest of vegetation on the slopes and in the base of the valley, limiting the sedimentary contribution to the talweg.…”