Unmodified lithic material at Olduvai Bed I: manuports or ecofacts?

The existence of high percentages of so-called manuports in the Olduvai sequence has given way to abundant papers on the behavioural explanation of such accumulations of raw material. For this paper, we performed a first-hand re-examination of the lithic collections of two of the most relevant sites in Olduvai Bed I (FLK Zinj and FLK North). The analysis has unearthed extremely significant differences between the unmodified lithic material (the so-called manuports) and the other stone collections, which has demanded the search for alternative hypotheses to explain the presence of the supposed manuports at these sites. Thus, we have revised the site formation processes and have compared them with other similar sedimentary contexts in Olduvai and in nearby lacustrine basins. On the basis of our findings, we demonstrate the existence of different sized clasts in low energy contexts, and propose a natural deposition as the answer to the existence of the supposed manuports at Olduvai Bed I. In all, our analysis suggests that a great part of the unmodified lithic material from the Olduvai sites is not indicative of human action but the product of natural causes, thus being ecofacts and not genuine manuports.