XRF OBSIDIAN ANALYSIS FROM AYACUCHO BASIN, HUAMANGA PROVINCE, SOUTHEASTERN PERU Martín Giesso1+, Hugo G. Nami2, Juan J. Yataco Capcha3, Michael D. Glascock4, Brandi L. MacDonald4 1Department of Anthropology, Northeastern Illinois University, Chicago, Il. 60625 2CONICET-IGEBA, Laboratorio de Geofísica “Daniel A. Valencio”, Departamento de Ciencias Geológicas, FCEN, UBA, Ciudad Autónoma de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina. 3Museo de Arqueología y Antropología, Universidad Nacional Mayor de San Marcos, Perú 4Archaeometry Laboratory, Research Reactor Center, University of Missouri, Columbia, MO, 65211. KEYWORDS: OBSIDIAN SOURCING, XRF, SOUTHERN ANDES, PERU. + Corresponding author: [email protected] Abstract In South America, obsidian was broadly used along the Andean Cordillera from North to South. Particularly in Peru, its use can be traced to the earliest human occupations, continuously through pre-Columbian times, to contemporary Andean agro-pastoralist societies. With the aim of distinguishing the provenance of obsidians from this country, this article reports new XRF analysis on a number of obsidians obtained in surface collections of the Ayacucho region. The analysis and source determination were made by XRF on 52 artifactsThe source assignments involved comparisons between the compositional data for the artifacts and the University of Missouri Research Reactor (MURR) XRF obsidian database for sources in Peru. After analyzing the sample, several obsidian sources were recognized and documented, all of them with small nodules not larger than ~4 cm which were recovered at Ñahuinpuquio and Marcahuilca hill that belong to the previously identified Puzolana source. Another identified source is the well known Quispisisa, which is placed 120 km south of the city of Ayacucho, and distributed through a vast region in central Peru. The results presented in this paper expand previous observations on the obsidian provenance at the Ayacucho Basin, and also expands the extension of the Puzolana source between Yanama and Huarpa hills, south of Ayacucho city. 1. INTRODUCTION In South America, obsidian was broadly used along the Andean Cordillera from North to South (e.g. Bigazzi et al. 1992; Hurliman 1993; Salazar 1992, Burger et al. 1994; Seelenfreund et al. 1996; Dorighel et al. 1999; Stern et al. 2000; Bellot-Gurlet el. 2002, Durán et al. 2004, 2012; Bellot- Gurlet et al. 2008; Ogburn et al. 2009; Ogburn 2011; Giesso et al. 2011; Cortegoso et al. 2012; Nami et al. 2015; among others). Particularly in Peru, its use can be traced to the earliest human occupations (e.g. MacNeish et al. 1980, 1981, 1983; Rademaker et al. 2014; Sandweiss et al. 1998; Yataco Capcha and Nami 2016), continuously through pre-Columbian times, to contemporary Andean agro- pastoralist societies (Burger and Asaro 1978, 1979; Brooks, Giesso and Glascock 1997). In order to characterize archaeological obsidian sources and provenance, diverse lines of investigations have been developed in Peru since the late 1970s (Burger 2006, Burger and Asaro 1979, 1982, 1993, Burger et al. 1998a,b,c; 2000a,b, 2006a,b, 2016; Burger and Glascock 2000a,b, 2002; Stanish et al. 2002; Jennings and Glascock 2002; Tripcevich 2009, 2010, 2011; Eerkens et al. 2010; Matsumoto et al. 2017). With the aim of distinguishing the provenance of obsidians from this Andean country, this article reports new XRF analysis on a sample of several obsidian artifacts from different sites of the Ayacucho region, south of Huamanga province, in the southeast of the country (Figure 1). Figure 1. Location map of the Ayacucho Basin and sample locations in southeastern Peru. 2. ARCHAEOLOGICAL BACKGROUND The Ayacucho Basin in southeastern Peru is a well-studied area in South American archaeology because during 1969-1972, a significant number of sites were discovered and studied by the interdisciplinary “Ayacucho Archaeological Botanical Project” (MacNeish 1969; 1971; 1976; 1978; MacNeish et al. 1970, 1980; 1981; 1983). In order to reevaluate and build on these previous investigations we analyzed a number of obsidian specimens collected in new research activities performed in Ayacucho. In this region the terrain is rugged and the geomorphology is the result of successive volcanic events that were subjected to fluvial erosional processes, eventually giving rise to the Ayacucho Basin (Morche et al. 1995:15). In our search for obsidian first we carefully studied the geological information (Morche et al. 1995:17-18). In this endeavor, two zones located north and south of Ayacucho city were surveyed (Figures 2 and 3). The northern area includes the Pacaicasa district, were we explored the eastern slope Marcahuilca hill and Pampachacra. There, at the Molinoyoq Formation (Nm-mo in Figure 2) five volcanic cones that reach altitudes of approximately 3,400 masl were detected. The explorations have been carried out at the foot of the Marcahuilca hill and about 800 meters from the Pikimachay cave (Figure 2:1). Also to the east a volcanic cone was recorded in the Huari Formation where the Huari/Wari archaeological site was built (Np-hu in figure 2: Sample field Nº2). Pampachacra is an extension of the Huari urban site, in the middle of terraces and cultivation areas obsidian debris was collected in the Ayacucho Formation (Nm-ay1 in Figure 2:3). To the south, in the Carmen Alto district, the explorations were performed between the Huari and Ayacucho Formations (Np-hu and Nm-ay1, Figure 2: 4), and seven volcanic cones registered near Ayacucho city (Morche et al. 1995: 17-18). Localities such as San Juan Bautista, Ñahuinpuquio, Cerro Yanama and Cerro Huarpa were surveyed (Figure 2-3). The prospected areas are composed of volcanic rocks, sediments, tobaceous and calcareous white scabs that surround the flanks of the volcanic cones (Morche et al. 1995; see Figure 3). In these areas, obsidian samples as natural nodules and artifacts were found. In general the nodules showed small dimensions mostly ranging between ~1 to 3-4 cm. As seen in Figure 4, the archaeological vestiges are represented by small tools, cores and debitage mostly of black and smoky translucent obsidian; however, one specimen of the “mahogany” variety was found. Salient information on the sites where obsidians were recovered is summarized in Table 1. Figure 2. Explored area in the Ayacucho basin (modified after Morche et al. 1995). Figure 3. General view of Marcahuilca hill where the Pikimachay cave (a) and Huarpa hill (b) are located. Figure 4. Examples of obsidian nodules and archaeological artifacts from Ayacucho basin. a) in situ nodules at Ñahuinpuquio source, b-c) small archaeological artifacts, probably a core or unifacial tool, d-e) Nodules from Marcahuilca hill (d) and Ñahinpuquio between Huarpa and Yanama hills (e). Environment Relation with Type of Sample Figure Site Type Site/Locality archaeological sample (n = 52 ) finds Talus of Archaeological White limestone Lithic flakes Lithic 2.1 artifacts Pikimachay Cave (S) 13°02’18.63” 2 (W) 74°13’41.45” Slopes of Source East of the Pikimachay cave. 2.1 Surface covered by crusts of Marcahuilca Hill white limestone One nodule - 2 (S) 13°02’33.28” and lithic artifacts (W) 74°13’19.82” Turquezayoq Archaeological Huari site 2.2 Fragments of Lithic (S) 13°03’23.53” 2 Huari pottery artifacts (W)74°11’55.56” Capillapata Archaeological “ 2.2 (S) 13°03’26.8” “ “ 9 (W) 74°11’57.15” Pampachacra Archaeological In front of Huari and in the 2.3 (S) 13°03’43.92” middle of cultivation farms “ “ 6 (W) 74’12’0.08” Ñahuinpuquio Canyon Source High zone of Quebrada 2.4 Ñahuinpuquio, between 31 (S) 13º11’42.22” Huarpa and Yanama hills. - Nodules (W) 74°12’27.84” Table 1. Salient information of the localities where the samples were recovered. 3. MATERIALS AND METHODS The analyzed samples (n = 52) were surface finds recovered during different visits in the late 2000s and systematic surveys carried out between 2015 and 2017. All specimens were analyzed by X-ray fluorescence (XRF) with equipment of the University of Missouri Research Reactor (MURR). The first group set analyzed using a Thermo Quantx ARL desk top, the equipment analyzes Mn, Fe, Zn, Rb, Sr, Y, Zr, Nb, and Th, with 120 second intervals. The second set was processed using a hand- held Bruker spectrometer (Tracer III-V). Peak deconvolution was accomplished using the Bruker spectral analysis package which enabled measurement of thirteen elements in most samples, including K, Ti, Mn, Fe, Zn, Ga, Rb, Sr, Y, Zr, Nb, Pb, and Th. The samples have to be placed individually, and can have any size (the Quantx is covered, so the samples have maximum dimensions) and the cycle lasts 3 minutes. The instruments were calibrated using compositional data from a series of 40 well-characterized source samples in the MURR obsidian reference collection as described in a report by Glascock and Ferguson (2012). Consensus values for the obsidian calibration sources were previously determined at MURR (using both NAA and ICP-MS) and other laboratories (XRF only). Concentration ranges for the reference samples span the range of probable concentrations for obsidian from different sources around the world. 4.0 RESULTS The detailed results by elements and provenience are respectively depicted in Table 2. To determine sources for obsidian artifacts a scatterplot of Rb versus Zr is shown in Figure 5. The results proved satisfactory for determining sources for all the analyzed samples. Thirty-nine of the artifacts came from the Quispisisa source, thirty-four came from Puzolana (Vilcas), and two were unable to be assigned. When analyzing the 3 main elements (Rb, Sr, Zr) we observe that Quispisisa has significantly higher Rb and Sr, but similar amounts of Zr, as seen in Fig 5. Strontium ranges from 100 to 144 ppm in Quispisisa, and from 41 to 75 ppm in Puzolana-Vilcas. Fig. 5. Scatterplot of Rb versus Zr for obsidian artifacts from sites in Ayacucho, Peru.