GEOCHEMICAL CHARACTERIZATION AND SOURCING OF LITHIC ARTIFACTS FROM THE MAKUYUNI BEDS LOCALITY 4, TANZANIA

Archaeological excavations at Makuyuni locality 4 (MK4) in northern Tanzania revealed abundant lithic artifacts, attributed to Homo erectus (0.63-0.78 Ma; Schwartz et al. 2011), in Lower to Middle Pleistocene lacustrine deposits surrounding Lake Manyara. This study uses geochemistry and petrography to characterize MK4 artifacts to infer the tool making behavior of early hominins based on their raw material acquisition.

The MK4 lithic artifacts excavated in this study were closely associated with remains of Bovidae, Equidae, and Elephantidae and are composed of both volcanic rock (20 tools, 45 cores, and 45 debitage flakes) and quartzite (72 tools, 59 cores, and 1004 debitage flakes). The 27 volcanic artifacts analyzed in this study are subdivided into three distinct groups (A, B, C) based on the abundance and type of phenocrysts (pyroxene, olivine, plagioclase, respectively). Samples of local bedrock exhibit petrographic features that map onto the same three textural groups represented by the artifacts. Major element compositions classify the Group B artifacts as basalt, whereas Group A and C artifacts have compositions ranging from basaltic trachyandesite to mugearite. All of the artifacts have similar trace element patterns, with more incompatible trace elements (e.g., Ce, La, Nb, Th, Ba) exhibiting progressively greater enrichment typical of lavas in rift settings. The patterns of Group B artifacts are similar to those in A and C, but with distinctly lower normalized concentrations. Samples of local bedrock have trace element patterns that are similar to the artifacts in the equivalent textural groups.

The textures and compositions of the Makuyuni tools are all represented by samples from local bedrock exposures. Furthermore, the compositions of the Makuyuni tools are sufficiently distinct from analyzed samples from other regional volcanic centers (e.g., Ngorongoro, Oldeani, or Natron), suggesting that the entire Makuyuni tool assemblage was derived solely from local (<6 km) exposures. These findings are in stark contrast with the more distal provenances (>300 km) inferred from lithic tools used by later hominins (Middle Stone Age; 200,000-130,000 BP) in the same region and support models of a progression in raw material acquisition and manufacture, from local to more distant sources over time.