SCRAP Obsidian Sourcing in Ontario

Last week, Dr. Peuramaki-Brown and I (Megan Williams) traveled from Calgary, Alberta to Hamilton, Ontario where we worked in the McMaster Archaeological XRF Lab (MAX Lab; http://maxlab.mcmaster.ca/ ). We brought with us the obsidian collected during the SCRAP 2014-2015 surface surveys at Alabama, in order to determine the source of each piece (i.e. the various volcanic regions/flows of Guatemala, Mexico, or “other”). This analysis will help us to place Alabama within the trading spheres of the ancient Maya world, which we hope will help in our on-going investigation of the site as a possible example of a rapid settlement related to resource development and management. Additionally, we hope this research will also contribute to larger discussions focused on questions of Maya social, political, and economic organization(s) during the Classic to Early Post-Classic periods.

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The MAX Lab at McMaster University (Photo from http://maxlab.mcmaster.ca/)

We are collaborating with Dr. Tristan Carter who graciously granted us permission to use the desktop Energy Dispersive X-Ray Fluorescence (EDXRF), in order to determine the elemental composition of each of the Alabama obsidian artifacts. These compositions are then compared to various source samples. For a concise, ‘not-too-sciency’ explanation of the technique, visit the following website and download the free document XRF Technology for Non-Scientists (http://info3.thermoscientific.com/XRFeBookDownload). The weekend was a fantastic opportunity for learning the procedures necessary to conduct EDXRF analysis on obsidian artifact and source materials; how to correctly interpret the data; and issues facing analyses using complex and expensive technology.

For the remainder of this post, I will briefly outline the analysis process for you. The artifacts were unpacked from their marked bags and cleaned using an ultrasonic cleaner. This step ensures that artifacts are free of any dirt or debris that might inhibit the x-ray beam from reaching the obsidian surface. This is an important example of considering the order of analyses, as any residue analysis must be done prior to this stage. Given that all of these pieces were surface collected, we decided not to pursue any residue analysis at this time.

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Artifacts being unpacked by Megan (Photo by M. Peuramaki-Brown)

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Megan cleaning artifacts in sonic cleaners (Photo by M. Peuramaki-Brown)

After being cleaned and rinsed with distilled water, we cautiously affixed the flattest surfaces of the obsidian pieces to the part of the sample tray that would be hit by the beam. Each tray is circular and had enough space for us to affix nineteen samples, plus the standard sample that would ensure the accuracy of our results. We filled up almost three trays with obsidian and ran them individually.

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Megan rinsing the cleaned artifacts with distilled water (Photo by M. Peuramaki-Brown)

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Dr. Peuramaki-Brown and Megan examining the individual artifacts to locate flat surfaces prior to affixing pieces to the trays for analysis (Photo by C. Cluney)

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Megan positioning the obsidian artifacts on the analysis tray (Photo by M. Peuramaki-Brown)

Each tray takes roughly three hours to analyze, so in our down time we were able to sit in on one of the McMaster Anthropology graduate student’s thesis defense (FYI: she nailed it). When analysis of the tray is complete, the data is printed and transferred into Excel, then element ratios are compared to those of obsidian source sample ratios in order to attribute source location.

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Megan loading tray into the desktop EDXRF (Photo by T. Carter)

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Entering artifact tray data into the computer prior to analysis (Photo by T. Carter)

Dr. Peuramaki-Brown and I thought we had a pretty good idea of where the majority of artifact materials had originated from, based on considerations of currently understood site occupation dates and location; however, our data has produced some extremely interesting and unexpected preliminary results. Watch for my undergraduate independent study and co-authored presentations/publications in the new year! These results will be further investigated in upcoming field seasons and laboratory analyses.

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Dr. Carter and Megan going over the surprising results of the XRF characterization

A big thank you to Dr. Carter and the staff of the MAX Lab at McMaster University for hosting us and letting us use their facilities.

Cheers,

Megan Williams

(Senior Undergraduate Student, Anthropology Program, Athabasca University)