Petrographic Characterization of Raw Material Sources at Oldupai Gorge, Tanzania

Abstract

Oldupai Gorge is located within the Ngorongoro Conservation Area, a UNESCO World Heritage Site in northern Tanzania along the western margin of the East African Rift System. Oldupai's sedimentary record contains inter-stratified stone tool industries associated with the Earlier, Middle, and Later Stone Age. While diachronic technological change is perceptible, the totality of locally available rocks remained largely unchanged through time. Here, thin section petrography, Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy, and Electron Probe Micro Analysis were employed to characterize source lithologies in the Oldupai region. One of our goals was to determine if outcrops have rock types with unique mineral assemblages amenable for sourcing lithic artifacts. Petrographic analysis of 62 lithologic samples collected in primary and secondary positions reveal discriminatory differences. More precisely, five outcrops have quartzites with unique mineral assemblages, five outcrops have meta-granites with unique mineral assemblages, Engelosin phonolite samples are texturally and mineralogically unique, and magmatic samples recovered in secondary position may be sourced to their volcanic center. Our results demonstrate it is feasible to discriminate source materials using mineralogy, which implies that sourcing lithic artifacts is possible. For proof of concept, we assign the source/s of previously described fuchsitic quartzite artifacts from three archaeological sites at Oldupai to two nearby outcrops. Additional archaeological testing will allow researchers to glean new understandings of hominin behavior and stone procurement in the Oldupai paleobasin.

Oldowan Technology Amid Shifting Environments ∼2.03–1.83 Million Years Ago

“…First, in every phase, lithic technology was produced mostly on quartzite, with other materials being less frequent. Macroscopic and petrographic data, compared to published reference collections (Favreau et al, 2020;Soto et al, 2020a,b), determined that the most likely sources for the raw materials employed at Ewass Oldupa were the outcrops of Naisiusiu, Naibor Soit, Endonyo Osunyai, and/or Oittii. However, chemical characterization and Linear Discriminant Analysis of Oldowan materials showed that up to three-quarters of the quartzite came from Naibor Soit, while strictly local rock from Naisiusiu was less commonly employed (Mercader et al, 2021).…”

Sourcing Oldowan and Acheulean Stone Tools in Eastern Africa

“…To this day, the combination of macroscopic and petrographic techniques has proven useful to delineate similarities and differences among quartzitic outcrops at Oldupai Gorge. For instance, two recent studies using a combination of macroscopic, petrographic, and geochemical techniques have shown that green quartzites are exclusive to two outcrops on a local scale, a fact that was corroborated by the petrographic identification of the mineral fuchsite that is responsible for the green colour in hand sample (Favreau et al 2020;Soto et al 2020a). The validation that quartz-rich outcrops can be differentiated from one another based on macroscopic and petrographic data is in line with a growing body of literature that counters the implicit assumption that it is unachievable on any spatial scale (e.g.…”

“…Moreover, some of these rhyolites were exposed to metasomatism by carbonatite magmatic doming in which additional elements were introduced into the rocks by circulating fluids (Finestone et al 2020). The HWK E site at Oldupai Gorge (Tanzania) (Figure 2) has yielded one Oldowan lithic manufactured from "altered but unmetamorphosed gabbro" (Hay 1976:185) that may be provenanced to the Tanzania Craton, although a closer Neoproterozoic outcrop has been proposed as an alternative source based on a petrogenetic analogue (Favreau et al 2020).…”

“…Leakey (1971) also noted the discovery of one obsidian core in Level 3, but its geological source remains in question, as does another piece made of gabbro (cf. Favreau et al 2020;Hay 1976). In a recent study, McHenry and de la Torre ( 2018) combined macroscopic, petrographic, X-ray diffraction, and WD-XRF techniques to assess lithic procurement strategies at the nearby site of HWK EE (~1.76-1.66 Ma) (Table 1; Figure 4).…”

“…Hay 1976;Kleindienst 1973;Kyara 1999;McHenry & de la Torre 2018;Tactikos 2005). The resultant belief that the local outcrops were largely undifferentiable from one another has since shown to be erroneous evidenced by recent characterisation studies complimented by archaeological testing (Egeland et al 2019;Favreau et al 2020;Mercader et al 2021;Soto et al 2020aSoto et al , 2020b. Aside from quartzite, the dynamic geological history of Eastern Africa led to the petrogenesis of various igneous, metamorphic, and sedimentary rock types (Cahen et al 1984), which have only recently begun to be comprehensively studied within the framework of archaeological research but have already offered revelatory insights into early hominin stone transport (Braun et al 2008).…”