The FLK Zinj paleolandscape: Reconstruction of a 1.84 Ma wooded habitat in the FLK Zinj-AMK-PTK-DS archaeological complex, Middle Bed I (Olduvai Gorge, Tanzania)

Abstract We have analyzed the phytolith content of 37 samples from the paleosol capped by Tuff IC dated 1.84 Ma within Middle Bed I at Olduvai Gorge, Tanzania. Samples were obtained from different trenches sampling an area of about 25 ha to document the paleovegetation associated with the abundant faunal remains and hominin artifacts in FLK, AMK, PTK and DS sites. The analysis reveals the abundance of globular granulate and forest indicator phytoliths (from 3% to 86% relative to the total number of phytoliths in the assemblages) attributed to woody plants, and of short cell grass phytoliths (up to 22%). The presence of palm phytoliths (up to 57%) attests for meso-haline soils in the area in agreement with the presence of the saline/alkaline Olduvai paleolake and one (or more) groundwater discharge areas (freshwater springs and/or wetland). Phytoliths provide botanical evidence for a mixed paleovegetation dominated by forest and woodland with patches of open-spaces occupied by grasses, prior to the deposition of Tuff IC. The presence of fern phytoliths in some assemblages suggest shaded and humid habitat, which supports the presence of freshwater (watercourses or springs) that might have attracted hominins and other animals. Yet, we have found that our phytolith extractions (residues) also include micrometric zeolites (chabazite, clinoptilolite, phillipsite), which attest that the phytolith signal in the Zinj paleosols is certainly affected by dissolution. This study completes the spatial analysis of the area and reveals that the wooded area extends north, south, and west of FLK Zinj, with palm trees preferentially located in the periphery, like the Zinj, AMK, and DS sites. The phytolith-inferred distribution of plants does not support the hypothesis that topography was influential in the location of these sites, particularly given that trees and/or shrubs were dominant all over. Rather, it is the presence of freshwater ponds that seem to have been the attractive factor for hominins at this particular place and time.