Geochemical and physical characterization of lithic raw materials in the Olduvai Basin, Tanzania

Charles P Egeland,Cynthia M Fadem,Ryan M Byerly,Cory Henderson,Curran Fitzgerald,Audax Z.P Mabulla,Enrique Baquedano,Agness Gidna

doi:10.1016/j.quaint.2019.09.036

Abstract

The invention and proliferation of stone tool technology in the Early Stone Age (ESA) marks a watershed in human evolution. Patterns of lithic procurement, manufacture, use, and discard have much to tell us about ESA hominin cognition and land use. However, these issues cannot be fully explored outside the context of the physical attributes and spatio-temporal availability of the lithic raw materials themselves. The Olduvai Basin of northern Tanzania, which is home to both a wide variety of potential toolstones and a rich collection of ESA archaeological sites, provides an excellent opportunity to investigate the relationship between lithic technology and raw material characteristics. Here, we examine two attributes of the basin's igneous and metamorphic rocks: spatial location and fracture predictability. A total of 244 geological specimens were analyzed with non-destructive portable XRF (pXRF) to determine the geochemical distinctiveness of five primary and secondary sources, while 110 geological specimens were subjected to Schmidt rebound hardness tests to measure fracture predictability. Element concentrations derived via pXRF show significant differences between sources, and multivariate predictive models classify geological specimens with 75–80% accuracy. The predictive models identify Naibor Soit as the most likely source for a small sample of three lithic artifacts from Bed II, which supports the idea that this inselberg served as a source of toolstone during the early Pleistocene. Clear patterns in fracture predictability exist within and between both sources and rock types. Fine-grained volcanics show high rebound values (associated with high fracture predictability), while finer-grained metamorphics and coarse-grained gneisses show intermediate and low rebound values, respectively. Artifact data from Bed I and II suggest that fracture predictability played a role in raw material selection at some sites, but other attributes like durability, expediency, and nodule size and shape were more significant.

Highlights

The study of raw materials has been embedded in analyses of the African Early Stone Age (ESA) for some time (Kleindienst, 1962; Stiles et al, 1974; Hay, 1976; Jones, 1979; Clark, 1980)
In terms of ranging behavior, ESA hominins gathered most of their raw materials during short forays to local conglomerates and/or surface outcrops (Braun et al, 2009a; Goldman-Neuman and Hovers, 2012; Kuman et al, 2018), they did occasionally engage in longer distance treks to both primary outcrops and secondary sources (Braun et al, 2008, 2013)
The two elements with concentrations certified by National Institute of Standards and Technology (NIST) and measured by the portable XRF (pXRF) in the granulite samples, titanium and strontium, show values of 22.0% and 2.0%, respectively

Summary

Introduction

The study of raw materials has been embedded in analyses of the African Early Stone Age (ESA) for some time (Kleindienst, 1962; Stiles et al, 1974; Hay, 1976; Jones, 1979; Clark, 1980). In terms of ranging behavior, ESA hominins gathered most of their raw materials during short forays (hundreds of meters to a handful of kilometers) to local conglomerates and/or surface outcrops (Braun et al, 2009a; Goldman-Neuman and Hovers, 2012; Kuman et al, 2018), they did occasionally engage in longer distance treks (between 10 and 40 kilometers) to both primary outcrops and secondary sources (Braun et al, 2008, 2013). These findings have important—and contested— implications for our understanding of ESA hominin land use and cognitive abilities (Plummer, 2004; Schick and Toth, 2006; Braun and Hovers, 2009; Braun, 2012, 2013; Toth and Schick, 2018)

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Discussion

Conclusion