Obsidian Subsource Identification in the Sierra de Pachuca and Otumba Volcanic Regions, Central Mexico, by ICP‐MS and DBSCAN Statistical Analysis

Abstract

Otumba and Sierra de Pachuca obsidian deposits in Central Mexico have been important sources of raw material since pre‐Hispanic times. Numerous archaeological investigations have suggested that the economical and political expansion of major Mesoamerican societies were linked to the control of obsidian sources and distribution of quarried material. Sierra de Pachuca contains several obsidian flows and numerous quarries throughout the region that were preferentially exploited by different cultures. The Otumba Volcanic Complex has four important obsidian domes, but three of them have not been studied in detail. A geochemical characterization of subsources from the Sierra de Pachuca and Otumba Volcanic Complex is an important step toward future sourcing of obsidian artifacts that would help provide insight into spheres of influence and trade by past cultures in Central Mexico. Having this purpose in mind, inductively coupled plasma mass spectrometry (ICP‐MS) was used to analyze obsidian samples collected from five separated locations at Sierra de Pachuca and four at Otumba, followed by statistical analysis (density‐based spatial clustering of applications with noise, DBSCAN). We were able to distinguish three chemically distinctive subsources in Sierra de Pachuca and three in Otumba. This study illustrates the importance of accurate characterization of obsidian raw material when attempting to define subsource usage.

Geochemical Variability in the Paredón Obsidian Source, Puebla and Hidalgo, Mexico: A Preliminary Assessment and Inter‐Laboratory Comparison

“…Studies of Mesoamerican obsidian sources have identified spatially and geochemically distinct variation at major sources such as Pachuca (Glascock ; Argote‐Espino et al . ), Otumba (Argote‐Espino et al . ) and Zaragoza‐Oyameles (Knight et al .…”

Projection-Based Classification of Chemical Groups for Provenance Analysis of Archaeological Materials

“…We found that all the artifacts assigned to the Sierra de Pachuca source group corresponded to green obsidian samples, without overlapping with any of the other groups. The Sierra de Pachuca is a well-known geological source renowned for its valuable green translucent volcanic glass [41,[44][45][46]. The grouping was also evaluated by means of a contingency table (Table 3), whose rows are the sources groups and the columns the result of the clustering.…”

“…It is important to note that larger sample sizes generate more complex overlapping, making group discrimination more difficult. The only groups with a clear separation from the other are Sierra de Pachuca and El Pizarrín-Tulancingo; this can be explained by the distinctive greater concentrations of zirconium and zinc of these sources compared to other regional deposits [44][45]. Zinapecuaro and Zacualtipan also show a wide dispersion of the data points, not forming compact groups.…”

“…For the first experiment we used 64 samples from El Paredón (Puebla), Otumba (state of Mexico), Sierra de Pachuca (Hidalgo), Oyameles (Puebla) and Zinapecuaro (Michoa-can); for the second experiment, we extracted the samples from Zinapecuaro and added 29 samples collected from Zacualtipan (Hidalgo) and El Chayal (Guatemala). A full description of the obsidian geological sources can be found in references [41,[44][45][46].…”

Elemental, isotopic, and geochronological variability in Mogollon‐Datil volcanic province archaeological obsidian, southwestern USA: Solving issues of intersource discrimination

“…Here, we summarize the elemental, isotopic, and geochronological exploratory research into successful discrimination of these important Southwestern sources of archaeological obsidian in order to provide a database and strategy to deal with this problem, one that is present in other volcanic provinces worldwide (e.g., Argote‐Espino, Solé, López‐Garcia, & Stepone, ; Brown, Reid, & Negash, ; Chataigner & Gratuze, ; Glascock, ; Morgan, Renne, Taylor, & WoldeGabriel, ; Poidevin, ; Poupeau et al., ; Sahle, Morgan, Braun, Atnafu, & Hutchings, ; Shackley & Sahle, ; Vogel, Nomade, Negash, & Renne, ; Weisler & Woodhead, ). In order to provide clarity beyond XRF, we have acquired Sr, Pb, and Nd isotopic data along with 40 Ar/ 39 Ar ages from sample splits for these sources (see Supplementary Document 1 for laboratory and instrumental methods for XRF, the isotopic analysis, and 40 Ar/ 39 Ar dating).…”