The East African Rift system created one of the world's most obsidian-rich landscapes, where this volcanic glass has been used to make tools for nearly two million years. In Kenya alone, there are > 80 chemically distinct obsidians along a 800-km north-south transect. Recently Brown et al. (2013) published their Kenyan obsidian database assembled since the 1980s. Specifically, they report elemental data measured by EMPA, ICP-MS, and WDXRF, providing a rich basis for future sourcing studies. Here we report our use of portable XRF (pXRF), calibrated specifically and directly to the database in Brown et al. (2013), to examine interactions between Later Stone Age forager-fishers and pastoralists near Lake Victoria. Regarding our calibration to the WDXRF and EMPA datasets of Brown et al. (2013), the elements of interest have very high correlations (R2 = 0.96–0.99) to our pXRF values, which show, on average, only a 2–5% relative difference from the published values. Use of pXRF data specifically calibrated to the datasets from Brown et al. (2013) greatly expands the impact of their work over three decades to catalog and characterize a multitude of Kenyan obsidians. Our focus here is investigating social contacts and exchange between late Holocene populations that included Kansyore forager-fishers and Elmenteitan pastoralists. Similarities and differences in their obsidian access provide new insights into long-term interactions between foragers and food producers in eastern Africa. We report new sourcing results for obsidian artifacts from six late Holocene rock shelters along the Winam Gulf of Lake Victoria. The patterns in obsidian access are consistent with changing interaction spheres that are relevant to understanding forager-fisher social identities and subsistence strategies during periods of economic and demographic change.
Bibliographical noteFunding Information:
We are indebted to Frank Brown and Harry Merrick for generously contributing obsidian specimens from Brown et al. (2013), which made this study possible. Additional specimens of Kenyan obsidian, which aided our compatibility tests, were contributed by Minghua Ren and were collected by Elizabeth Anthony and Jesus Velador, University of Texas-El Paso. We thank Curtis Runnels, Director, and Priscilla Murray, Curator, for access to the artifacts in the Gabel Museum of Archaeology at Boston University. Funding support was provided by the American School for Prehistoric Research and by Harvard University. Frahm's work was supported, in part, by the Department of Anthropology, Department of Earth Sciences, Institute for Rock Magnetism, Electron Microprobe Laboratory at the University of Minnesota. Research assistance was provided by Ravid Ekshtain and Liev Frahm. The pXRF instrument used in this study is part of the research infrastructure of the University of Minnesota's Wilford Laboratory of North American Archaeology, directed by Katherine Hayes. Funding for the instrument was provided by the College of Liberal Arts and by the Office of the Associate Dean for Research and Graduate Programs. We thank Nick Blegen, Matt Magnani, and especially Mary Prendergast for their constructive critiques of earlier drafts of this paper. Two anonymous reviewers provided helpful comments that improved the final version.
- Analytical cross-calibration
- Eastern Africa
- Forager-pastoralist interactions
- Lake Victoria
- Later Stone Age
- Obsidian artifact sourcing
- Portable XRF (pXRF)