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Phytoliths in modern plants and soils from Klasies River, Cape Region (South Africa)

Novello, Alice, Bamford, Marion K., van Wijk, Yvette, Wurz, Sarah
Quaternary international 2018 v.464 pp. 440-459
Anacardiaceae, Asteraceae, Celastraceae, Cyperaceae, Ericaceae, Leucadendron, Restionaceae, Vitaceae, charcoal, culms, fynbos, grasses, humans, leaves, morphs, paleoecology, phytoliths, rivers, seeds, shrubs, silica, soil, soil sampling, tissues, South Africa
The archaeological site of Klasies River is famous for the richness of its Middle Stone Age deposits, which offer the opportunity to document behaviors of early modern humans in Africa, as well as the paleoenvironmental context of their occupation of the area during the late Pleistocene. The Main Site deposits (dated to ca. 115 to 55 ka) include botanical remains such as seeds and charcoal, which suggests that micro-plant particles like phytoliths could also have been deposited. Yet, no phytolith reference collection based on both modern plant and soil material has been produced for Klasies River, which complicates attempts of phytolith analysis of the site's deposits. One of our challenges was therefore to initiate a new and comprehensive phytolith reference collection of modern plants and soils occurring today in the vicinity of Klasies. For this purpose, we processed phytoliths from 24 modern plant specimens and 16 soil samples from different vegetation patches, all located today in a perimeter <5 km2 around the Main Site. Our analyses indicate that ovate/orbicular and/or tabular polygonal phytoliths are the most recurrent and abundant morphotypes (>53% and up to 94%) produced in the leaf tissues of the Anacardiaceae, Asteraceae, Celastraceae, Ericaceae, Proteaceae, and Vitaceae species we studied, which are all eudicotyledoneous taxa. Regarding the Cyperaceae, Restionaceae, and one of the Proteaceae species (Leucadendron spissifolium, a fynbos shrub), they each produce distinct phytolith assemblages: the Restionaceae leaf/culm assemblage is dominated by psilate and decorated globular/spheroid phytoliths (94%), whereas the Cyperaceae leaf/culm content and the Proteaceae leaf content are both dominated by silicified papillae (-like) bodies (54% and 63%, respectively). Besides, both globular/spheroid and papillae (-like) phytoliths account for 34% and 8% in the fynbos soil collected. Our analyses also show that ovate/orbicular and/or polygonal phytoliths occur in very small amounts (<2%) in modern soils of the area although they are numerous in most of the eudicotyledoneous leaf tissues we analyzed. Conversely, grass silica short cell phytoliths are found abundantly in the soils collected in close proximity to the Main Site (>66%), where grasses do however occur sparsely in the current vegetation.