The impact of hydraulic processes in Olduvai Beds I and II, Tanzania, through a particle dimension analysis of stone tool assemblages

The effect of post-depositional processes on the formation of Plio-Pleistocene sites at Olduvai Gorge is the subject of considerable debate, due mainly to its implications for the behavioral interpretation of the Beds I and II assemblages. In light of this debate, here we contribute to the discussion that investigates the role of water flow in site formation at Olduvai. This is achieved by assessing the artifact size and shape ranges of lithic assemblages excavated by Mary Leakey from both Oldowan (FLK North Levels 3 and 1, FLK Zinj, FLK North Levels 6-1, Sandy Conglomerate and Deinotherium, HWKE Level 1) and early Acheulean (TK Lower and Upper Floor) sites. We apply grain size and shape statistical techniques to these stone tool assemblages in order to classify sites according to patterns in artifact dimensions. These patterns are then compared to those produced during experimental flaking, thus providing a referential framework against which the archaeological assemblages can be interpreted. Artifact size distribution results show pronounced differences between the archaeological and experimental assemblages. Most of the archaeological assemblages are characterized by a bimodal size trend that is opposed to the dominantly unimodal distribution seen in the flaking experiments. The few archaeological assemblages where the distribution is predominantly unimodal (TF Lower Floor, TK Upper Floor and FLK Zinj) also show a significant underrepresentation of smaller artifacts, when compared to the experimental distributions. Overall, the comparison of archaeological materials with experimental results enables a more accurate assessment of the impact of natural processes over the Bed I and II assemblages, and further, it helps to refine our understanding of taphonomic and behavioral contexts for the Oldowan and early Acheulean sites at Olduvai Gorge.