Later Stone Age Toolstone Acquisition in the Central Rift Valley of Kenya

Home , Elmenteitan, Glynn Isaac, Koobi Fora, Mass media in Kenya

Journal of Archaeological Science: Reports 18 (2018) 475–486

Contents lists available at ScienceDirect

Journal of Archaeological Science: Reports

journal homepage: www.elsevier.com/locate/jasrep

Later Stone Age toolstone acquisition in the Central Rift Valley of Kenya: T Portable XRF of Eburran obsidian artifacts from Leakey's excavations at Gamble's Cave II ⁎ ⁎⁎ Ellery Frahma,b, , Christian A. Tryonb, a Yale Initiative for the Study of Ancient Pyrotechnology, Council on Archaeological Studies, Department of Anthropology, Yale University, New Haven, CT, United States b Department of Anthropology, Harvard University, Peabody Museum of Archaeology and Ethnology, Cambridge, MA, United States

ARTICLE INFO ABSTRACT

Keywords: The complexities of Later Stone Age environmental and behavioral variability in East Africa remain poorly Obsidian sourcing defined, and toolstone sourcing is essential to understand the scale of the social and natural landscapes en- Raw material transfer countered by earlier human populations. The Naivasha-Nakuru Basin in Kenya's Rift Valley is a region that is not Naivasha-Nakuru Basin only highly sensitive to climatic changes but also one of the world's most obsidian-rich landscapes. We used African Humid Period portable X-ray fluorescence (pXRF) analyses of obsidian artifacts and geological specimens to understand pat- Hunter-gatherer mobility terns of toolstone acquisition and consumption reflected in the early/middle Holocene strata (Phases 3–4 of the Human-environment interactions Eburran industry) at Gamble's Cave II. Our analyses represent the first geochemical source identifications of obsidian artifacts from the Eburran industry and indicate the persistent selection over time for high-quality obsidian from Mt. Eburru, ~20 km distant, despite changes in site occupation intensity that apparently correlate with changes in the local environment. This result may indicate resilience of Eburran foraging strategies during environmental shifts and, potentially, a cultural preference for a specific lithic material that overcame its accessibility changes. Testing such hypotheses requires a more extensive program of obsidian artifact sourcing. Our findings demonstrate the great potential for sourcing studies in the Rift Valley as well as underscore the amount of work that remains to be done.

1. Introduction and the Sahel as far south as Lake Turkana (Wright et al., 2015; cf. Sutton, 1974; Holl, 2005), and the Eburran industry produced by for- The complex dynamics of Holocene interglacial environmental and agers in the Central Kenyan Rift Valley (e.g., Ambrose, 1984; Wilshaw, behavioral variability in East Africa remain poorly defined. Significant 2016). Cattle, sheep, and goat spread southward from northern to and often abrupt environmental changes include the return to near- eastern Africa by ~7 ka, resulting in a complex cultural and economic glacial conditions during the Younger Dryas event (∼12.9–11.7 ka), mosaic that was in place by 3 ka (di Lernia, 2013; Kusimba, 2003; Lane, followed by the African Humid Period (AHP, ~11–6 ka), and a return to 2013; Skoglund et al., 2017). more arid conditions (∼6–4 ka; e.g., Gasse, 2000; Tierney and A number of unanswered questions remain about the archaeology of deMenocal, 2013). Changes during the AHP are particularly striking, this timeframe. For example, do distinctive regional behavioral entities including the “Green Sahara” phase of northern Africa, with a number (e.g., archaeological industries like the Eburran) form because of of East African lakes expanding in size and depth, coincident with the adaptations to specific habitats, as a result of isolation from neigh- expansion of more forested ecotones (Butzer, 1972; Hamilton, 1982; boring groups, or as a deliberate expression of what Wiessner (1983) Bergner et al., 2009; Trauth et al., 2010). Archaeologically, a number of referred to as emblemic style? Does the spread of pastoralism reflect the regionally distinct artifact traditions are recognized, including the demic diffusion of groups along an expanding frontier or a series of Kansyore fisher-foragers of the Lake Victoria basin (Dale and Ashley, local adaptations as stock is transferred along existing social networks 2010), fisher-forager communities who produced the “dotted-wavy among foraging groups (cf. Lane, 2004; Prendergast, 2010; Skoglund line” pottery and barbed harpoons found throughout parts of the Sahara et al., 2017)? Answering these questions ultimately requires

⁎ Correspondence to: E. Frahm, Yale Initiative for the Study of Ancient Pyrotechnology, Council on Archaeological Studies, Department of Anthropology, Yale University, New Haven, CT, United States. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (E. Frahm), [email protected] (C.A. Tryon). https://doi.org/10.1016/j.jasrep.2018.01.042 Received 24 July 2017; Received in revised form 23 January 2018; Accepted 28 January 2018 2352-409X/ © 2018 Elsevier Ltd. All rights reserved. E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486 establishing the nature and strength of inter-group connections, which 2008; Drake et al., 2009; and Liritzis and Zacharias, 2011). In this is not straightforward, particularly using archaeological data. For- study, our pXRF measurements were directly calibrated and compared tuitously, artifacts made of obsidian are common at many AHP sites in to the published data of Brown et al. (2013) in order to determine the East Africa, particularly in Kenya, and identifying the geological artifacts' origins. We have previously documented that the XRF data- sources of these artifacts can enhance our understanding of the extent base of Brown et al. (2013) and our pXRF measurements are directly to which different regions – and, in turn, the populations within them – compatible (Frahm et al., 2017). were connected in the past. Our results for the Eburran Phases 3 and 4 at GC2 suggest that the There are > 80 geochemically distinct obsidian sources along an site's occupation history or local environment had no discernable effect 800-km stretch of Kenya between Lake Turkana on the Ethiopian – at least in this sample – on the variety or range of obsidian sources border and Lake Natron on the Tanzanian border (Brown et al., 2013). used for tool manufacture. Previously unpublished data for the site's use Of these, roughly two-thirds lie within Kenya's Naivasha-Nakuru Basin indicate a higher occupation intensity during the more humid Eburran and its surroundings, and there is now a fairly robust geochemical Phase 3, when the lake's shoreline was likely closer at GC2 than at database for source outcrops as well as Pleistocene-Holocene artifacts present. As the lakeshore retreated and, with it, the site's position at an made by foragers and pastoralists from sites in Kenya and Tanzania ecotone important to Eburran groups, the occupation intensity at GC2 (e.g., Merrick and Brown, 1984a, 1984b; Merrick et al., 1988, 1994; decreased, as indicated by the lower frequency of retouched tools and Mehlman, 1989; Coleman et al., 2008, 2009; Nash et al., 2011; Ndiema artifact discard rates in the later deposits. In both phases, the closest et al., 2011; Ambrose et al., 2012a, 2012b; Ferguson, 2012; Prendergast source – Mt. Eburru at ~20 km distant – was consistently exploited to et al., 2013; Faith et al., 2015; Blegen, 2017; Blegen et al., 2017; Frahm meet the demands for lithic material. This implies that demand for this et al., 2017). From the extant data, a few generalizations can be made. toolstone outweighed ecologically linked changes in its accessibility to First, foragers and pastoralists in the Lake Turkana basin appear to have GC2 occupants. This result might also indicate the resilience of Eburran used locally available obsidian sources, which means there is no strong foraging strategies during the transition from an earlier, more humid evidence in these data to support cultural connections between the interval and a later, drier one. Speculatively, these GC2 data might also Turkana region and the Naivasha-Nakuru Basin. Second, pastoralist mark the beginning of the widespread use of Mt. Eburru obsidian by groups relied extensively on sources within the Naivasha-Nakuru Basin, foragers across Kenya and Tanzania. Testing such hypotheses requires a transporting large quantities of obsidian across long distances (often more extensive program of obsidian sourcing in the region, and our ≥100 km), particularly to the south. Third, there has been persistent findings not only reveal the potential for such analyses but also un- movement of obsidian from the Naivasha-Nakuru Basin into the Lake derscore the amount of work that remains to be done. Victoria basin. Connections between these regions date to at least the Late Pleistocene (Faith et al., 2015; Blegen et al., 2017) and persist 2. Background throughout the Holocene, including portions of the AHP (Merrick and Brown, 1984a, 1984b; Frahm et al., 2017) that overlap in time with The GC2 rockshelter (0.55525° S, 36.08936° E, 1934 m) is an Kansyore sites in the Lake Victoria basin and assemblages attributed to overhang cut into an interface between Quaternary lacustrine sedi- the Eburran industry in the Naivasha-Nakuru Basin. ments and Pleistocene pyroclastics, where it formed during an early Apparent connections between foragers in the Lake Victoria basin Holocene highstand of Lake Nakuru (Figs. 1–2; Washbourn-Kamau, (e.g., Kansyore groups) and groups in the Naivasha-Nakuru Basin (e.g., 1971). Leakey excavated ~45 m2 at GC2 to a depth of ~8.5 m in Eburran producers) are based entirely on obsidian sourcing data from 1926–1929, and he recognized four “occupation levels” that include a sites in the Lake Victoria basin, that is, from sites ~200 km from the number of early-to-late Holocene LSA obsidian blade-based lithic in- sources. As yet, there are no published geochemical data on obsidian dustries that span the transition to food production (i.e. pastoralism) artifacts found at Eburran industry sites. Such data can serve as a means and the local adoption of ceramics. These different occupation levels to better understand the extent of connections between these two areas. were only summarily described in his 1931 book The Stone Age Cultures To initiate this, we focus on collections from Gamble's Cave II (GC2; of Kenya Colony.AsLeakey (1971:iv) notes in a new introduction to the Kenya), the type-site for Phases 3, 4, and 5 of the Eburran industry. In second printing of that book, “a very detailed report… on Gamble's particular, we focus on a collection of GC2 obsidian artifacts from L.S.B. Cave II, was sent to press in Paris, just before the outbreak of World War Leakey's 1920s excavations housed at Harvard University's Peabody II, but the whole report and all the illustrations and diagrams were Museum of Archaeology and Ethnology. This subsample of the GC2 mislaid or destroyed during the German Occupation.” assemblage reflects what Leakey (1931) termed the “fourth occupation In 1964, Glynn Isaac and Ronald Clarke excavated a 1 × 2 m stra- level” of GC2. He initially subdivided it into the Kenyan Aurignacian tigraphic section at GC2 to collect material for radiocarbon dating. Phases a and b, which were subsequently designated as the type de- Ambrose (1984) provides a summary of lithic and faunal assemblages posits for Phases 3 and 4 of the Eburran industry (see Ambrose et al., from the 1964 excavation. Materials from the Leakey and Isaac/Clarke 1980; Ambrose, 1984; Wilshaw, 2016). excavations formed the basis for a major revision of the Holocene Later Using state-of-the-art portable X-ray fluorescence analysis (pXRF), Stone Age (LSA) sequence in the Central Kenya Rift. The divisions are we chemically identified the geological sources of 239 GC2 obsidian based on stratigraphy as well as changes in retouched tool type and, in artifacts. pXRF instruments offer archaeologists several advantages over particular, a size decline in blade and backed piece length over time. techniques traditionally used for obsidian sourcing. First, pXRF is The early so-called “giant blade” Eburran Phases 1 and 2, which are not nondestructive, meaning that artifacts do not need to be polished, present at GC2, are dated to ~12 ka and 11.0–10.3 ka elsewhere in the powdered, dissolved, or discarded. Second, it can be conducted at a Central Kenya Rift (Wilshaw, 2016). These are followed by Eburran museum, in a field house, or even at an archaeological site. Third, it can Phase 3 and Phase 4, which are not very well dated at GC2. Reliable be rapid, often needing just a minute or two to measure dozens of dates are restricted to a number of similarly aged radiocarbon de- elements. The first two advantages were paramount in this study. terminations near the base of the Phase 3 deposits. Estimates from GC2 Recent studies demonstrate that newer pXRF instruments have tech- (based partially on inferred sedimentation rates) are generally con- nical advances (e.g., large-area Si drift detectors with high spectral sistent with those from other Eburran Phase 3 and Phase 4 assemblages, resolution, adaptive signal-processing electronics) that enable excellent which suggest an age of ~8.5–8 ka for Phase 3 and ~7.8–6 ka for Phase accuracy, reproducibility, and sensitivity (e.g., Frahm, 2014; Milić, 4(Ambrose, 1984; Ambrose et al., 1980; Bower et al., 1977; Protsch, 2014; Frahm and Feinberg, 2015; Newlander et al., 2015; Le 1978; Wilshaw, 2016). These are, in turn, overlain by the ‘small blade’ Bourdonnec et al., 2015; Campbell and Healey, 2016; Bonsall et al., Eburran Phase 5 (~4.5–1.8 ka) and by the Pastoral Neolithic Elmen- 2017; Orange et al., 2017; cf. older instruments in Potts and West, teitan industries from ~3.2–1.4 ka (Goldstein and Munyiri, 2017).

476 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Fig. 1. Map of the Central Rift Valley of Kenya, including the location of Gamble's Cave II (GC2) and the obsidian sources identiﬁed at GC2 in the Eburran Phases 3 and 4 deposits. The light blue shaded areas correspond to Wilshaw's (2012) lake level reconstructions ∼8 ka. Before that, ∼9.5 ka, the Nakuru-Elmenteita palaeo-lake reached all the way to – and formed – the GC2 rockshelter. See also the lake level reconstructions in Bergner et al. (2009) for their maximum extents. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)

GC2 is considered the type site for Eburran Phases 3 and 4 (as well cores made on angular spalls. These blades and bladelets were subse- as the Eburran Phase 5 and the Elmenteitan Neolithic industry; quently modiﬁed into several tool types, in particular a variety of Ambrose, 1984), and Phases 3 and 4 are the focus of our research. The backed pieces, with the larger blades segmented and transformed into Eburran Phase 3 and 4 lithic technological system is geared towards the smaller tools such as endscrapers and truncated/facetted pieces for the production of blades and bladelets from single or opposed platform production of small ﬂakes, bladelets, and burin spalls (Nelson, 1973;

Fig. 2. Stratigraphic section from Leakey's original excavations at GC2 (redrawn from Leakey, 1931: Figure 15; colors are arbitrary, selected for clarity).

477 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Newcomer and Hivernel-Guerre, 1974; Ambrose, 1984; Wilshaw, 2012, teeth) in Eburran 3 levels were used to support this scenario, with the 2016). expectation of greater fragmentation (and thus fewer complete Considerable research has focused on potential links among the specimens) with increased occupation intensity during Eburran Phase Eburran-producing groups' subsistence strategies, settlement locations, 4. and shifting altitudes of savannah-bush-forest ecotones within this Hypothesis 3. Greater occupation intensity correlates to increased reliance basin (e.g., Isaac, 1972; Ambrose et al., 1980; Ambrose, 1984, 1986, on local obsidian sources and greater diversity in the number of sources used. 2001; Ambrose and DeNiro, 1989; Ambrose and Sikes, 1991; Marean, This hypothesis predicts an increased reliance on local obsidian sources, 1992; Marean et al., 1994). Three main ecological zones exist at dif- as tools, which are subject to more intensive and/or prolonged uses, are ferent altitude ranges in the Nakuru-Naivasha Basin: savannah (low- increasingly made or replaced at the site as needed. Similarly, the land), bush (mid-range) and montane forest (highland). Human settle- diversity of toolstone materials brought to the site should increase with ment focus appears to track the position of the boundaries between occupation intensity as wider portions of the landscape are encountered them over time as they shifted in response to climatic changes (e.g., the during extended forays to procure toolstone or other resources (cf. bush and montane forest expands into lowland areas during wet times, Kuhn, 1991; Surovell, 2009), as foraging range tends to increase with the savannah expanded into higher altitudes in drier times). occupation duration (Hovers, 2009:158). The GC2 faunal assemblage appears to reflect at least some of these changes. Provenience data are poor for original faunal materials reported in Leakey (1931). Data reported from the Isaac and Clarke ex- 4. Materials and methods cavations consist of identifiable teeth only: 87 specimens from Phase 3 and 27 from Phase 4. Phases 3 and 4 are both dominated by small Here we report how we tested these hypotheses, in particular the bovids (Ambrose, 1984; Marean, 1992). Ambrose (1984) interprets the details of the sourced GC2 artifact assemblage, the pXRF instrument Eburran Phase 3 deposits as indicative of forest or bush conditions, and analytical protocols, our specialized calibration for direct com- based on the presence of bushbuck (Tragelaphus scriptus) and various patibility with the published datasets of Brown et al. (2013), and our duikers (Cephalophus sp.), consistent with evidence from Lake Nakuru means of matching GC2 artifacts to their sources. We followed the and Lake Naivasha for more humid conditions when the lakes had ex- procedures documented in Frahm et al. (2017), so readers interested in panded at this time and the lake margin was closer than at present additional details regarding our protocols and their quality assessments (Richardson and Dussinger, 1986; Bergner et al., 2003, 2009). In con- are directed to that publication. trast, the Phase 4 fauna are interpreted by Ambrose (1984) as indicative of a slightly more open bush and/or grassland landscape, suggested, in 4.1. Archaeological assessments of mobility and occupation intensity part, by higher proportions of reedbuck (Redunca cf. fulvorofula) in the Phase 4 deposits. This interpretation would be consistent with a general Ambrose's (1984) estimates of occupation intensity and frequency decline in lake size due to increased aridity that began ~6 ka or earlier are based on the number of retouched tools and on an inverse re- (Richardson and Dussinger, 1986; Maitima, 1991), which, therefore, lationship between artifact and faunal densities at the site, with faunal would have positioned GC2 farther from the lake margin in Phase 4 density estimated entirely on the number of recovered teeth. The in- than during Phase 3. ferences were that more such artifacts reflect more use of a site and that greater, more intensive occupation results in increased faunal frag- 3. Hypotheses mentation and, in turn, fewer identifiable teeth for the Eburran 4 deposits. In terms of the lithic assemblage, research since Ambrose's Because we are interested in the nature of diachronic changes (1984) hypotheses were formulated have emphasized that the number within the Eburran, we use archaeological and obsidian source datasets of retouched tools alone is insufficient to infer either the frequency or to test three hypotheses about the occupation history of GC2. intensity of site use. Specifically, Riel-Salvatore and Barton (2004; Barton and Riel-Salvatore, 2014) have shown that a superior measure is Hypothesis 1. Occupation intensity was greater at GC2 during Eburran the frequency of retouched tools relative to the “artifact volumetric Phase 3. This hypothesis is based on paleoenvironmental data from GC2 density,” that is, the total number of artifacts per excavated cubic meter and neighboring Eburran sites as well as theoretical models drawn from for a particular assemblage or deposit. Because retouched tools are behavioral ecology. In general, we expect more wooded nearshore often components of the transported toolkit, assemblages made by environments of Eburran Phase 3 at GC2 to provide a more dense and highly mobile groups that stay at a given locality for only a short time predictable resource base than the inferred drier and more open tend to have relatively more retouched tools than sites occupied by habitats during Eburran Phase 4, thereby supporting more intensive groups that stay longer at a particular place on the landscape. In the occupation at the site. A number of ethnographic and theoretical latter case, with increased site occupation duration, the number of re- studies (e.g., Dyson-Hudson and Smith, 1978; Wiessner, 1982, 1983; touched tools becomes swamped by the more numerous flakes, flake Ambrose and Lorenz, 1990 ; Kelly, 2013; Marean, 2016) suggest that fragments, and other debris associated with on-site tool production and (1), with predictable and dense resources on the landscape, hunter- upkeep. gatherers tend to have small ranges and make less frequent moves but Here we estimate occupation duration and intensity at GC2 by (2), when resource productivity and predictability decrease, their home calculating average artifact discard rates, measured by dividing artifact range sizes and mobility tend to rise. totals by estimated time span, inferred from available radiometric and Hypothesis 2. Occupation intensity was greater at GC2 during Eburran stratigraphic data. We also calculate the ratios of retouched tools to Phase 4. Based on data from the Isaac and Clarke excavations, Ambrose lithic artifact volumetric densities, as described by Riel-Salvatore and (1984) suggested, on the basis of patterning within the GC2 lithic and Barton (2004) and by Barton and Riel-Salvatore (2014). Age spans faunal data, more intensive occupation at GC2 occurred during Eburran follow those provided by Ambrose (1984). Artifact abundances were Phase 4 relative to Phase 3. He noted there were considerably more calculated using retouched tool counts reported by Ambrose (1984) and retouched tools in Phase 4 relative to Phase 3, which he interpreted as previously unpublished data on the total number of artifacts recovered increased occupation intensity. The Phase 4 retouched artifact from the 1964 Isaac and Clarke excavation at GC2 (collected in 1978 by assemblage showed reduced typological diversity relative to Phase 3, Charles Nelson and provided by him to us in 2017). Our obsidian interpreted as the outcome of greater spatial segregation of activities sourcing data focus on an available sample excavated by Leakey. We tied to more intensive occupation (Ambrose, 1984). Finally, the greater use abundance data from the Isaac and Clarke excavations because their number of complete and identifiable faunal elements (measured by improved excavation and recording techniques reduce the sample

478 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Fig. 3. Examples of sourced obsidian tools from the Eburran Phase 3 (left) and Phase 4 (right) deposits, showing that these tools, principally backed blades and lunates, decreased in size over time (backed blades shrank from 34 ± 11 mm to 27 ± 8 mm in length; Ambrose, 2002). biases due to the loss of smaller debris. Unfortunately, lithics from the Table 2 Isaac and Clarke excavation appear to have been lost (Wilshaw, 2012) Summary of the typological classiﬁcation of GC2 artifacts from the Eburran Phases 3 and and, thus, are no longer available for study. 4 deposits. Additional details are available in the supplementary online materials.

Eburran Phase 3 Eburran Phase 4 4.2. Analyzed GC2 assemblage Simplified types n % n % In 1935–1936, the Peabody Museum acquired 241 GC2 obsidian Backed piece, complete 62 51% 54 46% artifacts from L.S.B. Leakey, at the request of then-Director Hugh Backed piece, fragment 31 26% 21 18% Hencken, who sought a “strictly typical series representing the various Core 11 9% 20 17% ancient cultures of Kenya” (PMAE Accession File 36-6). All but two of Scraper 8 7% 11 9% fl the artifacts still had Leakey's attribution to Upper Kenyan Aurignacian Core edge maintenance ake 6 5% 7 6% Blade, outrepasse 2 2% Phase a or b, which today correspond to Eburran Phases 3 and 4, re- Flake fragment 1 1% spectively (Fig. 3). We sourced 239 obsidian artifacts: 121 (51%) from Retouched blade, complete 1 1% lower deposits (Eburran Phase 3) and 118 (49%) from the upper de- Retouched blade, fragment 2 2% posits (Eburran Phase 4). Thus, the assemblage is nearly evenly split Misc. retouched piece 1 1% 1 1% Total 121 118 between the phases, with only 2.5% relative difference. The total masses of the artifacts are also similar: 434.3 g in Phase 3 and 481.4 g in – ff Phase 4 a 10% di erence (Table 1). In addition, the proportions of unretouched flaking debris. However, retouched tools are often con- fi ffi artifact types identi ed in the phases, while not identical, are su - sidered to be among the most portable elements of the toolkit trans- ciently similar to allow their comparison for our purposes (Table 2). ported by foragers. For example, Eerkens et al. (2007) report that, The Peabody's sample consists largely of retouched artifacts among hunter-gatherer populations of the North American West, ob- (n = 203), with fewer cores (n = 31, including burins) and 16 un- sidian retouched pieces typically exhibit greater source diversity and, retouched pieces. It is clearly biased, attested by the near-absence of

Table 1 Summary of the obsidian sources for GC2 artifacts from the Eburran Phases 3 and 4 deposits. Additional details are available in the supplementary online materials.

Distance Elevation Eburran Phase 3 Eburran Phase 4

Obsidian source (km) (m asl) n % mass (g) % n % mass (g) %

Mt. Eburru outcrops 20 ∼2590 105 87% 368.0 85% 93 79% 433.2 90% Mundui/Sonanchi 30 ∼1950 11 9.1% 48.2 11% 15 13% 28.7 6.0% Baixia Estate/Ilkek 30 ∼2030 3 2.5% 14.0 3.2% 9 7.6% 19.0 3.9% Masai Gorge Rockshelter 30 ∼2050 1 0.8% 0.5 0.1% Menengai 35 ∼2020 1 0.8% 0.8 0.2% Hell's Gate 1/Ololbutot 1 40 ∼2100 1 0.8% 3.3 0.8% Total 121 434.3 118 481.4

479 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486 on average, are found farther from their sources, whereas unmodified archaeologists typically exclude small artifacts from pXRF-based sour- flakes tend to reflect fewer, closer sources. Similar trends have also cing studies (e.g., Sheppard et al., 2011; Golitko, 2011; Goodale et al., been noted by Conard and Adler (1997), Turq et al. (2013), and others 2012; Kellett et al., 2013; Galipaud et al., 2014; Coffman and Rasic, among Middle Paleolithic assemblages across Western Europe. Re- 2015; Millhauser et al., 2015). Frahm (2016), though, developed and touched or “finished” tools, particularly backed microliths (like those tested two methods for pXRF-based sourcing of small obsidian artifacts that dominate Eburran assemblages) may also be more suited for the using well-measured mid-Z elements with similar X-ray energies. We purposes of exchange between groups (Ambrose, 2002). Despite its used one of these techniques to minimize errors associated with XRF of shortcomings, our sample is therefore appropriate to explore obsidian small lithic size classes. In short, elements such as Rb, Sr, Y, Zr, and Nb source and landscape use in the early Holocene of the Central Kenyan are well measured using XRF and, due to their similar characteristic X- Rift Valley. ray energies, are affected by small specimen sizes in the same way, Hivernel (1974) studied all of the remaining material known from meaning that ratios between them can largely cancel out the size ef- Leakey's excavations of Eburran Phases 3 and 4 at GC2, stored in var- fects. Sr occurs at very low concentrations in most Kenyan obsidians, so ious museums across the U.K. and Kenya. She reports a total of 1551 its utility for discerning sources is small. Therefore, we base our source artifacts from Phase 3 and 1982 artifacts from Phase 4. Therefore, our identifications on ratios of Zr, Y, and Nb to Rb. As a result, these analysis of 239 artifacts represents a ~5–9% sample of the known identifications are based on four independent variables while size ef- Eburran Phases 3 and 4 material excavated and retained by Leakey. In fects have been minimized. terms of absolute (rather than relative) size, our sample contains the Fig. 5 is a scatterplot of Zr/Rb, Y/Rb, and Nb/Rb. Note that, for four largest number of obsidian artifacts with geochemical data and source of the six identified obsidian sources, we plot not only the WDXRF attributions currently published for any Holocene LSA site in Kenya (cf. values of Brown et al. (2013) but also our pXRF data for geological Merrick and Brown, 1984a, 1984b; Merrick et al., 1990; Nash et al., specimens from the same sources. We also plot their WDXRF data and 2011; Ndiema et al., 2011). our pXRF data for seven additional sources that were not identified among the GC2 artifacts. Analyzing geological specimens offers an extra 4.3. Instrument and settings check on our ability to reproduce the values in Brown et al. (2013). The published and our newly measured values directly overlap in this We used a Thermo Scientific Niton XL3t GOLDD+ analyzer in this scatterplot, demonstrating how well our measurements duplicate those study. It is outfitted with a 2-W, Ag-anode tube to produce an incident from Brown et al. (2013). Thus, we have high confidence in our iden- X-ray beam. The tube's voltage and current change in combination with tifications, and all of these data are included in the supplementary different X-ray filters to optimally fluoresce elements in different por- material. tions of the periodic table. The elements of primary interest – the so- called “mid-Z” elements – were measured for 30–45 s using the “main” 5. Results X-ray filter with a tube voltage of 40 kV and current of ≤50 μA. This model is also equipped with a 25-mm2 silicon drift detector that has a Here we document our estimates of occupation intensity as well as resolution ≤155 eV. The X-ray beam has a diameter of ∼8-mm. The the identified obsidian sources and differences in their exploitation internal camera facilitated positioning the artifacts over the beam, and between the two site phases. It is worth noting that Central Rift Valley a test stand was used for the most stable measurement conditions. obsidian sources principally occur as discrete primary outcrops – more often as localized flows, less often as blocks in welded tuffs and ig- 4.4. Correction and calibration nimbrites – rather than as secondary deposits of transported nodules (Ambrose, 2012). There is, of course, variability in the surface expres- Measured X-rays must be “corrected” for various physical phe- sions of these sources: some are obsidian flows that extend ∼2000 m, nomena in a specimen (X-ray absorption and attenuation, secondary while others are exposures < 200 m2. On occasion, where obsidian is and tertiary X-ray fluorescence, photoelectric emission, and so on). We exposed on a hillside, there is a colluvial scatter across the slope. The used the fundamental parameters (FP) approach, which has been de- regional topography, however, limits the alluvial transport of obsidian monstrated to yield greater accuracy than empirical methods (i.e., blocks cannot escape closed basins without outlets via gravity or (Heginbotham et al., 2010). The instrument has a factory-set calibration water transport). Particularly during the AHP, when the lakes greatly tested with certified reference materials (CRMs) principally from the expanded, secondary deposits more than a few kilometers from the United States' National Institute of Standards and Technology. We “fine- primary sources would have been underwater. Secondary obsidian de- tuned” our data with a custom calibration tailored to the datasets of posits at the base of Mt. Eburru attest to this. Given the lack of op- Brown et al. (2013). Specifically, to maximize compatibility with Brown portunities for obsidians to be spread over large areas by natural pro- et al. (2013), we used 27 specimens originally analyzed in their study. cesses, we have confidence in the collection locations. As documented in Frahm et al. (2017), twelve of the specimens were used as calibration standards, and the other fifteen served as secondary 5.1. Archaeological measures of occupation duration and intensity standards to evaluate our custom calibration and show how well the calibrated pXRF data replicates values in Brown et al. (2013). As shown Table 3 synthesizes artifact abundance and accumulation data for in Fig. 4, pXRF data for the mid-Z elements are highly correlated to GC2, based on material from the 1964 Isaac and Clarke excavations and their wavelength-dispersive XRF (WDXRF) data. After calibration, on age estimates from inferred sedimentation rates calculated by slopes of the best-fit lines nearly equal 1. As established in Frahm et al. Ambrose (1984). In this sample, the proportions of retouched tools and (2017), these elements exhibit only small differences (2–4% relative) total lithic debris differ significantly between the Eburran Phase 3 and compared to the data in Brown et al. (2013), and our calibration allows Phase 4 deposits (χ2 = 101.24, p < 0.01). These data show that the direct compatibility between our pXRF data and those in Brown et al. Eburran 3 strata (spits #1–13) have lower numbers of retouched tools (2013). (n = 322) but a higher artifact volumetric density (2953/m3), whereas Eburran 4 strata (spits #14–37) show more retouched tools (n = 407) 4.5. Procedures for small artifacts but a lower artifact volumetric density (1034 artifacts/m3). Therefore, the retouched tool-to-artifact volumetric density ratio is 0.1 for the Many of the GC2 artifacts are small, a known challenge for XRF Eburran Phase 3 strata and 0.4 for the Eburran 4 strata. Although these techniques (e.g., Davis et al., 1998; Eerkens et al., 2007; Shackley, numbers should be regarded with caution because of the many as- 2011, 2012; Freund, 2014; Escola et al., 2016). Consequently, sumptions underlying them, estimated artifact discard rates are nearly

480 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486 Rb Y

400 300

R = 0.988 R = 0.994

300 200

200 100 WDXRF (Brown et al. 2013) WDXRF (Brown et al. 2013)

100 0 100 200 300 400 0 100 200 300 pXRF (ppm, calibrated) pXRF (ppm, calibrated) Zr Nb

3500 600

3000 R = 0.986 R = 0.969 500 2500

2000 400

1500 300 1000 WDXRF (Brown et al. 2013) WDXRF (Brown et al. 2013)

500 200 500 1500 2500 3500 200 300 400 500 600 pXRF (ppm, calibrated) pXRF (ppm, calibrated)

Fig. 4. Our pXRF data for the elements of interest are highly correlated to the WDXRF data of Brown et al. (2013), and after calibration, slopes of the best-fit lines nearly equal 1 (dotted lines). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) twice as high in the Eburran Phase 3 levels (∼6.2 artifacts/year) as in reliance on local sources and use of a greater diversity of sources than in Eburran Phase 4 (∼3.2 artifacts/year), implying that more intensive Phase 4. Toolstone from these diverse obsidian sources may have been occupation occurred earlier rather than later in the site's history. acquired either by direct access or through contact with neighboring These findings suggest lower intensity occupations (i.e., fewer ar- groups. tifacts discarded per year) and increased mobility (i.e., relatively fewer retouched tools) during Eburran Phase 4 relative to Eburran Phase 3 at fi GC2. Such results do not support Ambrose's (1984) original inter- 5.2. Identi ed obsidian sources pretation of GC2's occupation history (our Hypothesis #2) but do fl support interpretations that drier, more open habitats associated with Six obsidian sources are re ected among the artifacts (Figs. 6 to 8). Eburran Phase 4 structured settlement strategies (Hypothesis #1). We The most abundant source is also the closest: Mt. Eburru, ~20 km from – would expect greater occupation intensity during Eburran Phase 3 to GC2, is the source for 79 87% of the artifacts in the two phases. There correlate with increased lithic reduction intensity. Testing this hy- are multiple primary outcrops and secondary deposits on the north- pothesis, however, is difficult given the available sample, which is eastern slope of Eburru (Brown et al., 2013), including a Late Holocene dominated by backed pieces that are replaced, not resharpened, during obsidian quarry (i.e., GsJj50) discussed by Goldstein and Munyiri ∼ their use (Hiscock, 2006). Cores are rare and mostly (n = 30; 97%) (2017). At this quarry, which lies at 2570 m asl, excellent quality made on relatively thin blade segments that have little potential for obsidian crops out as very large blocks, and there is a sizable debris extensive reduction prior to discard. While Goldstein (2014) provides a scatter from reducing them (Brown et al., 2013; Goldstein and Munyiri, ∼ useful approach to estimating the extent of endscraper reduction, many 2017). Above this quarry, up to elevations of 2600 m asl, there are of the GC2 artifacts were made on blade blanks that were snapped, additional outcrops, some with quarrying debris (Brown et al., 2013). ∼ – perhaps deliberately, so comparisons of endscraper size at discard to Below it, as far as 4 5 km to the northeast, there are a few outcrops of fi reconstructed original blade length provides a poor estimate of reduc- low-quality obsidian as well as secondary deposits, speci cally water- tion intensity. rolled, -rounded, and -abraded cobbles within lacustrine sediments Obsidian source identification provides a means to assess the shape (Brown et al., 2013). The obsidian textures that occur in the GC2 tools and size of the territory used by Eburran Phase 3 and 4 foragers. For the appear more consistent with the high-elevation quarrying sites (i.e., “ ” more intensive Eburran Phase 3 occupations, we predict increased quality is excellent, Brown et al., 2013) than low-elevation deposits (e.g., “granular,”“flow banding and small phenocrysts are common,”

481 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Fig. 5. Three-dimensional scatterplot of Zr/Rb, Y/Rb, and Nb/Rb for the GC2 artifacts and a variety of Kenyan obsidian sources, including published data and our new pXRF analyses. Table 1 summarizes the results. All data plotted here are available in the supplementary online materials.

Table 3 2013). In contrast, the “Ilkek” exposure is an isolated outcrop of pre- Summary of artifact composition, density, and accumulation rate for GC2 based on the dominately low-quality obsidian in small nodules (Brown et al., 2013). 1964 Isaac and Clarke excavations. Artifact totals from Ambrose (1984) and Nelson Thus, we hypothesize that “Baixia Estate” represents the origin of this (personal communication, 2017), and age spans from Ambrose (1984). obsidian variety. The “Masai Gorge Rockshelter” source is a chill zone Eburran 3 Eburran 4 (i.e., where the lava rapidly cooled via contact with the existing rock) exposed in a cliff face (Brown et al., 2013). The “Menengai” obsidian Spit numbers 1–13 14–37 source is exposed in a caldera wall, where fair-quality obsidian seams Excavated area (m2)22 occur throughout pumiceous layers (Brown et al., 2013). Lastly, the Excavated thickness (m) 1.3 2.3 “ ” Excavated volume (m3) 2.6 4.6 Hell's Gate 1/Ololbutot 1 obsidian source has two elementally in- Minimum age (yr BP) 7266 5784 distinguishable exposures ~6 km apart. The “Hell's Gate 1” exposure is Maximum age (yr BP) 8510 7266 a chill zone in a cliff wall, and the observed material was “very poor Age span (yr) 1244 1482 obsidian for artifact manufacture, having many inclusions” (Brown Artifacts/year 6.2 3.2 “ ” Retouched tools (n) 322 407 et al., 2013). The Ololbutot 1 facies, however, consists of large blocks, Debris (n) 7357 4351 occasionally a meter in diameter, some of which are excellent quality Artifact total (n) 7679 4758 (Brown et al., 2013). Consequently, we presume that “Ololbutot 1” was Retouched tools (%) 4.2 8.6 the exposure exploited in antiquity. Note that, for both the Baixia Es- 3 Artifacts volumetric density (artifacts/m ) 2953 1034 tate/Ilkek and the Hell's Gate 1/Ololbutot 1 obsidian varieties, the Retouched tools: artifact volumetric density 0.1 0.4 higher-quality obsidian exposures are marginally closer to GC2, meaning that we are also using the more conservative geographic ori- “opaque green with a granular texture,” Brown et al., 2013). Given this gins. and that there is evidence of extensive quarrying at the outcrops, our working hypothesis is that the GC2 artifacts are most likely to reflect 5.3. Diachronic view acquisition from these quarrying sites or similar ones. Five obsidian sources are supplementary to Mt. Eburru, all ≥30 km Within our sample, both phases are dominated (~79–87%) by the from GC2. The “Mundui/Sonanchi” source has two chemically indis- closest obsidian source (Mt. Eburru), which lies at or near the margin tinguishable exposures ~3 km apart (Brown et al., 2013). The “Mundui (~20 km) of what is often considered the daily range for foragers (e.g., Estate” exposure is a ~40-m-long ridge, partly covered by lacustrine Surovell, 2009). In both phases, almost all of the artifacts (∼98–99%) sediments, that contains fair-quality obsidian as loose, “football-sized came from the same three obsidian sources: Mt. Eburru, Mundui/So- blocks… with numerous pumice inclusions” (Brown et al., 2013). The nanchi, and Baixia Estate/Ilkek, all ~30 km or less from GC2. Each of “Lake Sonanchi Crater” exposure, however, has excellent-quality ob- the other three sources that are ≥30 km away – Masai Gorge Rock- sidian blocks, occasionally half a meter in size, accessible within the shelter, Menengai, and Hell's Gate 1/Ololbutot 1 – is reflected by a crater wall (Brown et al., 2013). The “Baixia Estate/Ilkek” source single artifact. Of these three sources, the farther two only occur in consists of two obsidian exposures, approximately ∼9 km apart, that Phase 3, and the nearest one only occurs in Phase 4. However, given the cannot be elementally distinguished. The “Baixia Estate” facies has abundance of Mt. Eburru obsidian (20 km away), the mean source-to- “very high quality obsidian” exposed in a road cut into a quarry, in site distances in both phases are essentially the same: 21.4 ± 3.8 km in which volcanic tuff containing obsidian blocks was extracted, and this Eburran Phase 3 and 22.1 ± 4.1 km in Eburran Phase 4. Note that geological unit extends at least several hundred meters (Brown et al., these values use linear distances between GC2 and the sources. An

482 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Eburran Phase 3 Eburran Phase 4

2% 8% 9% 13%

By number

87% 79% Mt. Eburru outcrops Mundui/Sonanchi Baixia Estate/Ilkek Masai Gorge Rockshelter

3% 4% Menengai 11% 6% Hell's Gate 1/Ololbutot 1

By mass

85% 90%

Fig. 6. Proportions of the obsidian sources identified in the Eburran Phases 3 and 4 deposits, both by number of artifacts and by mass. actual path on the ground between this site and each source would be as well as the drier condition during Eburran Phase 4, as suggested by longer. Even without Mt. Eburru, the difference between the phases the fauna, which may have compelled larger home ranges and, thus, overlaps within a standard deviation: 30.9 ± 2.7 km during Eburran more interactions with distant areas. Neither expectation is strongly Phase 3 and 30 km (i.e., these sources are roughly equidistant) during supported by our available data. Artifacts from Phase 3 originate from Eburran Phase 4. Still, the two most distant obsidian sources – Me- more sources (n = 5) relative to Phase 4 (n = 4); however, this does not nengai (35 km away) and Hell's Gate 1/Ololbutot 1 (40 km away) – are significantly differ from an even or random distribution between the only found among artifacts from the earlier Eburran Phase 3. two phases (χ2 = 0.45, p = 0.83). Similarly, more of the Eburran 4 Based on our estimates of artifact discard rates and retouched tool sample originated from non-local obsidian sources (21.2%) relative to frequencies, we expect the more intensive Eburran 3 occupations to the Eburran 3 sample (13.2%), but this difference is not supported at sample a more diverse array of obsidian sources, as the diversity of the p < 0.05 level (χ2 = 2.67, p = 0.10). toolstone tends to increase as greater portions of the landscape are used We note also that that there is no significant difference in the ele- during more prolonged occupations. We also expect the Eburran 3 oc- vation of the sources used between Phases 3 and 4. Overall, the mean cupations to show increased reliance on local (> 20 km distant) elevations for these two phases are similar, with means overlapping at sources. This is, in part, due to the inferred greater occupation intensity one standard deviation: 2509 ± 209 m asl in Eburran Phase 3 and

Mt. Eburru outcrops 93 49 27 13 10 2 1 1 1 1

e Mundui/Sonanchi 15 2 4 4 1

Baixia Estate/Ilkek 7 2 2 1

Masai Gorge Rockshelter 1

Obsidian sourc Menengai 1

Hell's Gate 1/Ololbutot 1 1 t e e e Core Scraper Flake fragment Blade, outrepass Misc. retouched piec Backed piece, fragment Backed piece, complete Retouched blade, fragmen Retouched blade, complete Core edge maintenance flak Simplified types

Fig. 7. Number of GC2 obsidian artifacts classiﬁed both by lithic type and by source.

483 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Eburran Phase 3 Eburran Phase 4

5% 6% 7% 9% Backed piece, complete 9% Backed piece, fragment 46% Core 51% 17% Scraper

26% Others

18%

Fig. 8. Proportions of the lithic types identiﬁed in the Eburran Phases 3 and 4 deposits.

2461 ± 250 asl in Eburran Phase 4. These mean values are skewed by Lake Naivasha ~10–20 km from Mt. Eburru (see Goldstein and Munyiri, the abundance of Mt. Eburru obsidian at 2590 m asl. Excluding Mt. 2017 for review). This pattern has been interpreted as an example of Eburru from the calculations results in lower mean altitudes: controlled access to specific resources or landscape facets via social 1979 ± 47 m in Eburran Phase 3 and 1983 ± 41 km in Eburran Phase and/or physical means (cf. Robertshaw, 1990; Ambrose, 2012; 4. These elevation ranges, however, clearly overlap within a single Goldstein and Munyiri, 2017). The antiquity of this pattern is difficult standard deviation. It is also worth noting that both the highest ob- to discern, particularly as the exploited obsidian sources for Eburran sidian source (Mt. Eburru at ∼2590 m) and lowest source (Mundui/ Phase 5 assemblages (which precede the Elmenteitan strata) have not Sonanchi at ∼1950 m) were the two most commonly exploited, at least yet been determined. Limited support for this speculative scenario may based on the Peabody Museum's sample. be found in the Lake Victoria basin ~200 km away, where Mt. Eburru obsidian accounts for about 25% of the obsidian during the early Ho- locene (when only foragers are present) but 53% of the late Holocene 6. Discussion assemblages made by foragers and 67% of the studied pastoralist El- menteitan sites (Merrick and Brown, 1984a, 1984b; Frahm et al., 2017). Paleoenvironmental proxies from GC2 and neighboring lakes in- These data may suggest either (a) increased use over time of Mt. Eburru dicate a habitat shift from a more wooded, closed nearshore setting obsidians by foragers in the Lake Victoria basin or (b) obsidian acqui- during Eburran Phase 3 to a more open, grassy, and drier setting during sition by late Holocene foragers through some form of interaction with Eburran Phase 4. The results here suggest that this change in habitat Elmenteitan groups. was paralleled by a decline in occupation intensity over time. Given the apparent preference for occupations near the forest-savanna ecotone by Eburran foragers, the GC2 pattern can reasonably be interpreted as a 7. Conclusions change in the site's position or role within a broader settlement strategy, shifting from an intensely used site near the ecotone boundary The Naivasha-Nakuru Basin of Kenya's Central Rift Valley is a region to one farther from the boundary and, hence, used more rarely (cf. that is not only highly sensitive to climatic changes but also one of the Ambrose, 1986; Ambrose and Sikes, 1991; Ambrose, 2001). We would world's most obsidian-rich landscapes, allowing us to investigate the expect this change to be reflected in the types of lithic resources used relationship between environmental change and behavioral adaptations given that a number of chemically distinct obsidian outcrops occur over the course of the Holocene. The effect of these changes on Eburran within the vicinity of the site and would have been available to its past LSA hunter-gatherer populations has been one such focus of research in occupants. However, despite being able to attribute all 239 GC2 arti- past studies, in particular those of Ambrose and colleagues (e.g., facts in our sample to their sources, our results indicate no significant Ambrose, 1984, 1986; Ambrose and Sikes, 1991). GC2 serves as the differences between Eburran Phases 3 and 4 in terms of the diversity of type site for the early to middle Holocene Eburran Phases 3 and 4, sources used, use of non-local sources, or altitude of the outcrops used. which likely sample an earlier, more humid interval and a later, drier In short, changes in the settlement pattern appear to have had no one, respectively. Our analysis of occupation data for GC2 suggests a measurable impact on the types of toolstone being used, at least within greater intensity during the more humid Eburran Phase 3, when the the biased sample that Leakey sent to the Peabody Museum. lake's shoreline was likely closer to the site than it is at present. As the The lack of temporal differences in obsidian sources may indicate lake retreated (and, with it, the site's position at an important ecotone), the resilience of Eburran foraging strategies and the ability of a cultural occupation intensity declined, as measured by both the lower frequency preference for particular types of stone to overcome changes within the of retouched tools and by the reduced artifact discard rates in the local environment that would have impacted its availability. While Eburran Phase 4 deposits. speculative, the persistent use Mt. Eburru obsidian observed in Eburran Using pXRF, we analyzed 239 obsidian artifacts from GC2 housed at Phases 3 and 4 at GC2 may indicate the early stages of a wider phe- Harvard's Peabody Museum of Archaeology and Ethnology and attrib- nomenon of the preferred use of this lithic material at many Kenyan and uted them to six obsidian sources using a WDXRF database published by Tanzanian sites, a pattern that reached its apogee with Elmenteitan Brown et al. (2013). Comparison between the two phases suggest that pastoralist groups. Mt. Eburru obsidian is the dominant lithic material the site's occupation history or local environment had no discernable at Elmenteitan sites regardless of source distance (at times ~200 km effect – at least within this sample – on the variety or range of obsidian away), suggesting regular mechanisms for the supply and movement of sources used for tool manufacture, with the closest source (Mt. Eburru this toolstone, to the near-exclusion of contemporary “Savanna Pastoral at ~20 km away) consistently used to meet the supply demands for Neolithic” groups, who relied instead on the obsidian sources south of lithic raw material. This implies that the demand for this material

484 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486 outweighed any changes in the difficulty of its acquisition by GC2 oc- Kenyan obsidian sources and Late Quaternary artifacts with NAA and XRF. In: cupants. Speculatively, the GC2 data might also mark the beginning of Presented at the Annual Meeting of the Society for American Archaeology, Memphis, Tennessee. the widespread use of Mt. Eburru obsidian by groups of foragers Ambrose, S.H., Slater, P., Ferguson, J., Glascock, M., Steele, I., 2012b. Obsidian source throughout central and southern Kenya and northern Tanzania. Testing survey and Late Quaternary artifact sourcing in Kenya: implications for early modern such a hypothesis requires, in part, a new, more extensive program to human behaviour. In: Presented at the Annual Meeting of the Palaeoanthropology Society, Memphis, Tennessee. determine the obsidian sources exploited by Eburran foragers. Our re- Barton, C.M., Riel-Salvatore, J., 2014. The formation of lithic assemblages. J. Archaeol. sults here demonstrate the potential for such analyses and underscore Sci. 46, 334–352. the amount of work that remains to be done. Bergner, A.G.N., Trauth, M.H., Bookhagen, B., 2003. Paleoprecipitation estimates for the Lake Naivasha basin (Kenya) during the last 175 k.y. using a lake-balance model. Glob. Planet. Chang. 36, 117–136. Acknowledgements Bergner, A.G.N., Strecker, M.R., Trauth, M.H., Deino, A., Gasse, F., Blisniuk, P., Dühnforth, M., 2009. Tectonic and climatic control on evolution of rift lakes in the – Frank Brown passed away while this manuscript was under review, Central Kenya Rift, East Africa. Quat. Sci. Rev. 28, 2804 2816. Blegen, N., 2017. The earliest long-distance obsidian transport: evidence from the and given the importance of his decades of work to the success of this ∼200 ka Middle Stone Age Sibilo School Road Site, Baringo, Kenya. J. Hum. Evol. project, we wish to dedicate this paper to his memory. Harry Merrick 103, 1–19. also generously contributed the collection of geological obsidian spe- Blegen, N., Faith, J.T., Mant-Melville, A., Peppe, D.J., Tryon, C.A., 2017. The middle stone age after 50,000 years ago: new evidence from the Late Pleistocene sediments of the cimens used for our calibration to Brown et al. (2013). Viva Fisher Eastern Lake Victoria Basin, Western Kenya. PaleoAnthropology 2017, 139–169. (Senior Registrar), Kara Schneiderman (Director of Collections), Diana Bonsall, C., Elenski, N., Ganecovski, G., Gurova, M., Ivanov, G., Slavchev, V., Zlateva- Loren (Director of Academic Partnerships) and Emily Pierce Rose Uzanova, R., 2017. Investigating the provenance of obsidian from Neolithic and Chalcolithic sites in Bulgaria. Antiquity 91 (356), e3. (Curatorial Assistant for Academic Partnerships) facilitated access to Bower, J.R.F., Nelson, C.M., Waibel, A.F., Wandibba, S., 1977. The University of the artifacts in the Peabody's collections. The Peabody's artifacts were a Massachusetts' Later Stone Age/Pastoral ‘Neolithic’ comparative study in Central gift of the East African Archaeological Expedition via Dr. L.S.B. Leakey, Kenya: an overview. Azania 12, 119–146. Brown, F.H., Nash, B.P., Fernandez, D.P., Merrick, H.V., Thomas, R.J., 2013. Geochemical F.S.A., 1936. Charles Nelson generously provided his unpublished data composition of source obsidians from Kenya. J. Archaeol. Sci. 40, 3233–3251. on the total number of artifacts recovered from the 1964 Isaac and Butzer, K.W., 1972. Environment and Archaeology. Methuen & Co., London. Clarke excavations. Ravid Ekshtain provided valuable research support Campbell, S., Healey, E., 2016. Multiple sources: the pXRF analysis of obsidian from – for the pXRF and lithic analyses, and she was key in getting this project Kenan Tepe, S.E. Turkey. J. Archaeol. Sci. Rep. 10, 377 389. Coffman, S., Rasic, J.T., 2015. Rhyolite characterization and distribution in central started. Support was provided by the American School of Prehistoric Alaska. J. Archaeol. Sci. 57, 142–157. Research, Harvard University and the University of Minnesota's De- Coleman, M.E., Ferguson, J.R., Glascock, M.D., Robertson, J.D., Ambrose, S.H., 2008. A partment of Anthropology, Department of Earth Sciences, and Institute New Look at the Geochemistry of Obsidian From East Africa. 39. International Association for Obsidian Studies Bulletin, pp. 11–14. for Rock Magnetism. The pXRF instrument utilized for this study is part Coleman, M., Robertson, J.D., Ferguson, J.R., Glascock, M.D., Ambrose, S.H., 2009. of the research infrastructure of the University of Minnesota's Institute Further studies into the geochemistry of obsidian from Kenya. In: Presented at the for Rock Magnetism (IRM). Funding for the instrument came, in part, Annual Meeting of the Society for American Archaeology, Atlanta, Georgia. Conard, N.J., Adler, D.S, 1997. Lithic reduction and hominid behavior in the Middle from the University of Minnesota's Grant-in-Aid of Research, Artistry, Paleolithic of the Rhineland. J. Anthropol. Res. 53 (2), 147–175. and Scholarship (GIA) Program, awarded to Joshua Feinberg, Gilbert Dale, D., Ashley, C.Z., 2010. Holocene hunter-fisher-gatherer communities: new per- Tostevin, and Kyungsoo Yoo. spectives on Kansyore using communities of Western Kenya. Azania: Archaeol. Res. Afr. 45, 24–48. Davis, M.K., Jackson, T.L., Shackley, M.S., Teague, T., Hampel, J.H., 1998. Factors af- Appendix A. Supplementary data fecting the energy-dispersive X-ray fluorescence (EDXRF) analysis of archaeological obsidian. In: Shackley, M.S. (Ed.), Archaeological Obsidian Studies: Method and Theory. Plenum, New York, pp. 159–180. Supplementary data to this article can be found online at https:// di Lernia, S., 2013. The emergence and spread of herding in northern Africa: A critical doi.org/10.1016/j.jasrep.2018.01.042. reappraisal. In: Mitchell, P., Lane, P. (Eds.), The Oxford Handbook of African Archaeology. Oxford University Press, Oxford, pp. 527–540. ff fl References Drake, B.L., Nazaro , A.J., Prufer, K.M., 2009. Error assessment of portable X-ray or- escence spectrometry in geochemical sourcing. SAS Bull. 32 (3), 14–17. Dyson-Hudson, R., Smith, E.A., 1978. Human territoriality: an ecological reassessment. Ambrose, S.H., 1984. Holocene Environments and Human Adaptations in the Central Rift Am. Anthropol. 80, 21–41. Valley, Kenya (PhD). University of California. Eerkens, J., Ferguson, J., Glascock, M.D., Skinner, C., Waechter, S., 2007. Reduction Ambrose, S.H., 1986. Hunter-gatherer adaptations to non-marginal environments: an strategies and geochemical characterization of lithic assemblages: a comparison of ecological and archaeological assessment of the dorobo model. Sprache und three case studies from western North America. Am. Antiq. 72, 585–597. Geschichte in Afrika 7, 11–42. Escola, P.S., Hocsman, S., Babot, M.P., 2016. Moving obsidian: the case of Antofagasta de Ambrose, S.H., 2001. Middle and Later Stone Age settlement patterns in the central Rift la Sierra basin (Southern Argentinean Puna) during the late Middle and Late Valley, Kenya: Comparisons and contrasts. In: Conard, N. (Ed.), Settlement Dynamics Holocene. Quat. Int. 422, 109–122. of the Middle Paleolithic and Middle Stone Age. Kerns Verlag, Tübingen, Germany, Faith, J.T., Tryon, C.A., Peppe, D.J., Beverly, E.J., Blegen, N., Blumenthal, S., Chritz, K.L., pp. 21–43. Driese, S.G., Patterson, D., 2015. Paleoenvironmental context of the Middle Stone Ambrose, S.H., 2002. Small things remembered: Origins of early microlithic industries in Age record from Karungu, Lake Victoria Basin, Kenya, and its implications for human Subsaharan Africa. In: Elston, R., Kuhn, S. (Eds.), Thinking Small: Global Perspectives and faunal dispersals in East Africa. J. Hum. Evol. 83, 28–45. on Microlithic Technologies. Archaeological Papers of the American Anthropological Ferguson, J.R., 2012. Chapter 12: X-ray fluorescence of obsidian: approaches to calibra- Association, No. 12, pp. 9–29. tion and the analysis of small samples. In: Shugar, A.N., Mass, J.L. (Eds.), Handheld Ambrose, S.H., 2012. Obsidian dating and source exploitation studies in Africa: im- XRF for Art and Archaeology. Leuven University Press, Leuven, pp. 401–422. plications for the evolution of human behavior. In: Liritzis, I., Stevenson, C. (Eds.), Frahm, E., 2014. Characterizing obsidian sources with portable XRF: accuracy, re- Obsidian and Ancient Manufactured Glasses. University of New Mexico Press, producibility, and field relationships in a case study from Armenia. J. Archaeol. Sci. Albuquerque, pp. 56–72. 49, 105–125. Ambrose, S.H., DeNiro, M.J., 1989. Climate and habitat reconstruction using stable Frahm, E., 2016. Can I get chips with that? Obsidian sourcing down to the microdebitage carbon and nitrogen isotope ratios of collagen in prehistoric herbivore teeth from with portable XRF. J. Archaeol. Sci. Rep. 9, 448–467. Kenya. Quat. Res. 407–422. Frahm, E., Feinberg, J.M., 2015. Reassessing obsidian field relationships at Glass Buttes, Ambrose, S.H., Lorenz, K.G., 1990. Social and ecological models for the Middle Stone Age Oregon. J. Archaeol. Sci. Rep. 2, 654–665. in southern Africa. In: Mellars, P. (Ed.), The Human Revolution: Behavioral and Frahm, E., Goldstein, S.T., Tryon, C.A., 2017. Late Holocene forager-fisher and pastoralist Biological Perspectives in the Origins of Modern Humans. Edinburgh University interactions along the Lake Victoria shores, Kenya: perspectives from portable XRF of Press, pp. 3–33. obsidian artifacts. J. Archaeol. Sci. Rep. 11, 717–742. Ambrose, S.H., Sikes, N.E., 1991. Soil carbon isotope evidence for Holocene habitat Freund, K.P., 2014. Obsidian consumption in Chalcolithic Sardinia: a view from Bingia 'e change in the Kenya Rift valley. Science 253, 1402–1405. Monti. J. Archaeol. Sci. 41, 242–250. Ambrose, S.H., Hivernel, F., Nelson, C.M., 1980. The taxonomic status of the Kenya Galipaud, J.-C., Reepmeyer, C., Torrence, R., Kelloway, S., White, P., 2014. Long-distance Capsian. In: Leakey, R.E.F., Ogot, B.A. (Eds.), Proceedings of the 8th Panafrican connections in Vanuatu: new obsidian characterisations for the Makué site, Aore Congress of Prehistory and Quaternary Studies, 1977. The International Louis Leakey Island. Archaeol. Ocean. 49, 110–116. Memorial Institute for African Prehistory, Nairobi, pp. 248–252. Gasse, F., 2000. Hydrological changes in the African tropics since the Last Glacial Ambrose, S.H., Ferguson, J., Glascock, M., Slater, P., 2012a. Chemical fingerprinting of Maximum. Quat. Sci. Rev. 19, 189–211.

485 E. Frahm, C.A. Tryon Journal of Archaeological Science: Reports 18 (2018) 475–486

Goldstein, S.T., 2014. Quantifying endscraper reduction in the context of obsidian ex- Milić, M., 2014. PXRF characterisation of obsidian from central Anatolia, the Aegean and change among early pastoralists in southwestern Kenya. Lithic Technol. 39, 3–19. central Europe. J. Archaeol. Sci. 41, 285–296. Goldstein, S.T., Munyiri, J.M., 2017. The Elmenteitan obsidian quarry (GsJj50): new Millhauser, J.K., Fargher, L.F., Heredia Espinoza, V.Y., Blanton, R.E., 2015. The geopo- perspectives on obsidian access and exchange during the pastoral Neolithic in litics of obsidian supply in Postclassic Tlaxcallan: a portable X-ray fluorescence study. Southern Kenya. Afr. Archaeol. Rev. 34, 43–73. J. Archaeol. Sci. 58, 133–146. Golitko, M., 2011. Provenience investigations of ceramic and obsidian samples using laser Nash, B.P., Merrick, H.V., Brown, F.H., 2011. Obsidian types from Holocene sites around ablation inductively coupled plasma mass spectrometry and portable X-ray fluores- Lake Turkana, and other localities in northern Kenya. J. Archaeol. Sci. 38 (6), cence. Fieldiana Anthropol. 42, 251–287. 1371–1376. Goodale, N., Bailey, D., Jones, G., Prescott, C., Scholz, E., Stagliano, N., Lewis, C., 2012. Ndiema, K.E., Dillian, C.D., Braun, D.R., Harris, J.W.K., Kiura, P.W., 2011. Transport and pXRF: a study of inter-instrument performance. J. Archaeol. Sci. 39, 875–883. subsistence patterns at the transition to pastoralism, Koobi Fora, Kenya. Hamilton, A.C., 1982. Environmental History of East Africa: A Study of the Quaternary. Archaeometry 53, 1085–1098. Academic Press, London. Nelson, C.M, 1973. A Comparative Analysis of Twenty-Nine Later Stone Age Occurrences Heginbotham, A., Bezur, A., Bouchard, M., Davis, J.M., Eremin, K., Frantz, J.H., in East Africa. Ph.D. Dissertation. Department of Anthropology, University of Glinsman, L., Hayek, L.-A., Hook, D., Kantarelou, V., Germanos Karydas, A., Lee, L., California at Berkeley. Mass, J., Matsen, C., McCarthy, B., McGath, M., Shugar, A., Sirois, J., Smith, D., Newcomer, M.H., Hivernel-Guerre, F., 1974. Nucleus Sur Eclat: technologie et utilization Speakman, R.J., 2010. An evaluation of inter-laboratory reproducibility for quanti- par differentes cultures prehistoriques. Bull. Soc. Prehist. Fr. 71, 119–128. tative XRF of historic copper alloys. In: Mardikian, P. (Ed.), Proceedings of the Newlander, K., Goodale, N., Jones, G.T., Bailey, D.G., 2015. Empirical study of the effect International Conference on Metal Conservation, Charleston, South Carolina, USA, of count time on the precision and accuracy of pXRF data. J. Archaeol. Sci. Rep. 3, October 11–15, 2010. Clemson University Press, pp. 244–255. 534–548. Hiscock, P., 2006. Blunt and to the point: changing technological strategies in Holocene Orange, M., Le Bourdonnec, F.-X., Bellot-Gurlet, L., Luglie, C., Dubernet, S., Bressy- Australia. In: Lilley, I. (Ed.), Archaeology of Oceania: Australia and the Pacific Leandri, C., Scheffers, A., Joannes-Boyau, R., 2017. On sourcing obsidian assem- Islands. Blackwell Publishing, Malden, MA, pp. 69–95. blages from the Mediterranean area: analytical strategies for their exhaustive geo- Hivernel, F., 1974. A study of the Kenya Capsian of Gamble's Cave (Kenya) and its re- chemical characterization. J. Archaeol. Sci. Rep. 12, 834–844. lationship with other industries. MA Thesis. University College, London. Potts, P.J., West, M., 2008. Portable X-ray Fluorescence Spectrometry: Capabilities for In Holl, A.F.C., 2005. Holocene “aquatic” adaptations in North tropical Africa. In: Stahl, A.B. Situ Analysis. Royal Society of Chemistry. (Ed.), African Archaeology. Blackwell Publishing, Malden, MA, pp. 174–186. Prendergast, M.E., 2010. Kansyore fisher-foragers and transitions to food production in Hovers, E., 2009. The Lithic Assemblages of Qafzeh Cave. Oxford University Press. East Africa: the view from Wadh Lang'o, Nyanza Province, Western Kenya. Azania 45, Isaac, G.Ll., 1972. Comparative studies of site locations in East Africa. In: Ucko, P., 83–111. Tringham, R., Dimbelby, G.W. (Eds.), Man, Settlement, and Urbanism. Duckworth, Prendergast, M.E., Mabulla, A.Z.P., Grillo, K.M., Broderick, L.G., Seitsonen, O., Gidna, London, pp. 165–176. A.O., Gifford-Gonzalez, D., 2013. Pastoral Neolithic sites on the southern Mbulu Kellett, L.C., Golitko, M., Bauer, B.S., 2013. A provenance study of archaeological ob- Plateau, Tanzania. Azania: Archaeological Research in Africa 48, 498–520. sidian from the Andahuaylas region of southern Peru. J. Archaeol. Sci. 40, Protsch, R., 1978. The chronological position of Gamble's Cave II and Bromhead's Site 1890–1902. (Elmenteita) of the Rift Valley, Kenya. J. Hum. Evol. 7, 101–109. Kelly, R.L., 2013. The Lifeways of Hunter-Gatherers: the Foraging Spectrum, 2nd edition. Richardson, J.L., Dussinger, R.A., 1986. Paleolimnology of mid-elevation lakes in the Cambridge University Press. Kenya Rift Valley. Hydrobiologia 143, 167–174. Kuhn, S.L., 1991. "Unpacking" reduction: lithic raw material economy in the mousterian Riel-Salvatore, J., Barton, C.M., 2004. Late pleistocene technology, economic behavior of West-Central Italy. J. Anthropol. Archaeol. 10, 76–106. and land-use dynamics in southern Italy. Am. Antiq. 69, 257–274. Kusimba, S.B., 2003. African Foragers: Environment, Technology, Interactions. Altamira Robertshaw, P., 1990. Early Pastoralists of South-western Kenya. British Institute in Press, Walnut Creek, CA. Eastern Africa, Memoir 11, Nairobi. Lane, P., 2004. The ‘moving frontier’ and the transition to food production in Kenya. Shackley, M.S., 2011. Chapter 2: an introduction to X-ray fluorescence (XRF) analysis in Azania 39, 243–264. archaeology. In: Shackley, M.S. (Ed.), X-Ray Fluorescence Spectrometry (XRF) in Lane, P., 2013. The archaeology of pastoralism and stock-keeping in East Africa. In: Geoarchaeology. Springer, pp. 7–44. Mitchell, P., Lane, P. (Eds.), The Oxford Handbook of African Archaeology. Oxford Shackley, M.S., 2012. Portable X-ray fluorescence spectrometry (pXRF): the good, the University Press, Oxford, pp. 585–602. bad, and the ugly (online essay). In: Archaeology Southwest Magazine. Spring issue, Le Bourdonnec, F.-X., Bellot-Gurlet, L., Lugliè, C., Bressy-Leandri, C., 2015. Archéométrie pp. 26. de l'obsidienne: déchi ffrer la circulation d'une matière première. Nouv. Archeol. Sheppard, P., Irwin, G., Lin, S., McCaffrey, C., 2011. Characterization of New Zealand (138), 23–27. obsidian using PXRF. J. Archaeol. Sci. 38, 45–56. Leakey, L.S.B., 1931. The Stone Age Cultures of Kenya Colony. Cambridge University Skoglund, P., Thompson, J.C., Prendergast, M.E., ... Pinhasi, R., Krause, J., Reich, D., Press, Cambridge. 2017. Reconstructing prehistoric African population structure. Cell 171, 59–71. Leakey, L.S.B., 1971 [1931]. The Stone Age Cultures of Kenya Colony, Reprinted with a Surovell, T.A., 2009. Toward a Behavioral Ecology of Lithic Technology: Cases from New Introductory Note. Frank Cass and Company Limited, London (1971 [1931]). Paleoindian Archaeology. University of Arizona Press. Liritzis, I., Zacharias, N., 2011. Chapter 6: Portable XRF of Archaeological Artifacts: Sutton, J.E.G., 1974. The aquatic civilization of Middle Africa. J. Afr. Hist. 15 (4), Current Research, Potentials and Limitations. In: Shackley, M.S. (Ed.), X-Ray 527–546. Fluorescence Spectrometry (XRF) in Geoarchaeology. Springer, pp. 109–142. Tierney, J.E., deMenocal, P.B., 2013. Abrupt shifts in Horn of Africa hydroclimate since Maitima, J.M., 1991. Vegetation response to climatic change in Central Rift Valley, the Last Glacial Maximum. Science 342, 843–846. Kenya. Quat. Res. 35, 234–245. Trauth, M.H., Maslin, M.A., Deino, A.L., Junginger, A., Lesoloyia, M., Odada, E.O., Olago, Marean, C.W., 1992. Hunter to herder: large mammal remains from the hunter-gatherer D.O., Olaka, L.A., Stretcker, M.R., Tiedemann, R., 2010. Human evolution in a occupation at Enkapune ya Muto rock-shelter, Central Rift Valley, Kenya. Afr. variable environment: the amplifier lakes of Eastern Africa. Quat. Sci. Rev. 29, Archaeol. Rev. 10, 65–127. 2981–2988. Marean, C.W., 2016. The transition to foraging for dense and predictable resources and its Turq, A., Roebroeks, W., Bourguignon, L., Faivre, J.-P., 2013. The fragmented character impact on the evolution of modern humans. Philos. Trans. R. Soc. B 20150239. of Middle Palaeolithic stone tool technology. J. Hum. Evol. 65, 641–655. Marean, C.W., Mudida, N., Reed, K.E., 1994. Holocene paleoenvironmental change in the Washbourn-Kamau, C.K., 1971. Late Quaternary lakes in the Nakuru-Elmenteita basin, Kenyan Central Rift as indicated by micromammals from Enkapune Ya Muto Kenya. Geogr. J. 137, 522–535. Rockshelter. Quat. Res. 41, 376–389. Wiessner, P., 1982. Risk, reciprocity and social influences on !Kung San economics. In: Mehlman, M.J., 1989. Late Quaternary Archaeological Sequences in Northern Tanzania Leacock, E., Lee, R. (Eds.), Politics and History in Band Societies. Cam-bridge (Ph.D. thesis). University of Illinois, Urbana. University Press and Editions de la Maison des Sciences de l'Homme, Cambridge and Merrick, H.V., Brown, F.H., 1984a. Rapid chemical characterization of obsidian artifacts Paris, pp. 61–84. by electron microprobe analysis. Archaeometry 26 (2), 230–236. Wiessner, P., 1983. Style and social information in Kalahari san projectile points. Am. Merrick, H.V., Brown, F.H., 1984b. Obsidian sources and patterns of source utilization in Antiq. 48, 253–276. Kenya and Northern Tanzania: some initial findings. Afr. Archaeol. Rev. 2, 129–152. Wilshaw, A., 2012. An Investigation into the LSA of the Nakuru-Naivasha Basin and Merrick, H.V., Brown, F.H., Connelly, M., 1988. Sources of the obsidian at Ngamuriak and surround. In: Central Rift Valley, Kenya: Technological Classifications and Population other Southwestern Kenyan sites. In: Robertshaw, P. (Ed.), Early Pastoralists of South- Considerations. Cambridge University (Ph.D. dissertation). western Kenya. British Institute of Eastern Africa, Nairobi. Wilshaw, A., 2016. The current status of the Kenya Capsian. Afr. Archaeol. Rev. 33, Merrick, H.V., Brown, F.H., Nash, W.P., 1994. Use and movement of obsidian in the Early 13–27. and Middle Stone Ages of Kenya and Northern Tanzania. In: Childs, S.T. (Ed.), Wright, D.K., Forman, S.L., Kiura, P., Bloszies, C., Beyin, A., 2015. Lakeside view: so- Society, Culture, and Technology in Africa. Masca Research Papers in Science and ciocultural responses to changing water levels of Lake Turkana, Kenya. Afr. Archaeol. Archaeologypp. 29–44. Rev. 32, 335–367.

486