Thursday, February 23, 2012

NEWS From the Survey: Obsidian XRF

Hi everyone! It's Julie here.

I'm still working with the survey data at Calixtlahuaca, trying to make some sense of how neighborhoods were organized culturally and economically. Specifically, were the material differences in class, consumer preferences, ritual, and procurement distributed in clusters in space. Most of the data I use in my analysis is ceramic and seems to suggest that there was limited social clustering based on class and no social clustering based on consumer preferences. I'm still not done with the analysis yet, so there is more information to wring out of the data. However, the obsidian data tells a different story, one where different neighborhoods obtained obsidian from different sources. In fact, neighborhoods in different regions of the site seem to have similar proportions of obsidian. But I'm getting a head of myself.

The obsidian data I'm looking at are the results of an XRF study of 155 pieces of surface collection obsidian representing 19 of the 20 neighborhood units at the site. These pieces of obsidian were sent to Dr. Michael Glascock and his team at the Missouri University Research Reactor. They took care of the chemical analysis and source attribution of the Calixtlahuaca survey obsidian. I got back a file with the data from the XRF analysis and the sources for each piece of obsidian.

We at Calixtlahuaca have obsidian from six known and one unknown source. The green obsidian is confirmed to come from Pachuca. We also have grey obsidian from Ucareo, Zinapecuaro, Otumba, Malpais, and Zacualtipan. The overall distribution of grey obsidian by source is:

Ucareo 56.4%

Zinapecuaro 0.7%

Otumba 38.6%

Malpais 0.7%

Zacualtipan 1.4%

So most of the grey obsidian from the survey comes from West Mexican sources! We kind of thought that was going to be the case, but its awesome to have it confirmed.

Another interesting thing that came out of this analysis is what kinds of artifacts are being made with this obsidian. Of my sample, we had 86 pieces of obsidian for which we also had information on lithic technology. This was provided by Dr. Bradford Andrews from Pacific Lutheran University. Based on that information, the people of Calixtlahuaca preferred some obsidian for specific uses over others.

Looking at our two most common grey obsidian, Ucareo and Otumba, the preferences were:

Ucareo Otumba

Bipolar Technology 65% 30%

Prismatic Blades 84% 9%

Unifaces and Bifaces 0% 100%

I think that's pretty neat!

So, I'm still looking at the data and making interpretations. This is by no means a final report, but a work in progress. But Angela kept poking me to post this information. Hope you are as excited as I am.