Mineral assemblages and low energy sedimentary processes in the FLK-Zinj, DS, PTK and AMK complex palaeolandscape (Olduvai Gorge, Tanzania)

The mineralogical composition of the clay stratum (level 22) that contains the FLK Zinj-DS-PTK-AMK complex, the only example of pene-contemporaneous early Pleistocene sites occurring on the same palaeolandscape and simultaneously covered by the same ash fall tuff, shows significant intra-site and inter-site differences. Overall, level 22A is related to a more hydrologically closed system, with higher salinity and alkalinity than level 22B. Both levels show fresher water was entering the system from the DS area during deposition. Textural analysis of the studied samples shows great microporosity and abundant edge-to-edge and edge-to-face contacts between crystals. These results have major repercussions for the interpretation of the archaeological assemblages in the FLK Zinj-DS-PTK-AMK palaeolandscape. First, this implies that two distinct archaeological levels formed at different times with different environmental conditions in most of these localities. Second, textural analyses provide evidence that no important sedimentary compaction took place after the deposition of this layer. This affects interpretations of palaeolandscape geomorphology. Third, it shows that the sedimentary processes during all the clay sequence occurred in very low-energy conditions. This reinforces that no significant physical forces disturbed the original configurations of materials contained within these assemblages and reinforces their autochthony. Behavioural interpretations can, thus, be more solidly built upon the conception that those sites preserve most of their original in situ properties.