Regional Clay Sampling

Angela Huster

This summer, I spent a week taking twenty-eight clay samples from across the Toluca Valley and immediately adjacent areas for INAA analysis. Don Cato, one of our local crew members from the excavation, helped by driving in incredibly convoluted loops around the area, and patiently explaining to  bystanders about what I was doing.

I kept crossing the construction route of another major water line to supply Mexico City. Occasionally, it was useful, such as here, where I needed a sample from below substantial modern fill.

These samples should help us identify where our previously sourced archaeological ceramics were made. Because there are only three other sites in the region with sourced ceramics, we have several chemical clusters in our archaeological ceramics that probably represent particular subregions, but we don't know where on the physical landscape those subregions are. More specifically, the new clay samples should help with three specific questions:

What chemical elements are the most geographically variable across the Toluca Valley and therefore the most useful for identifying source areas within the region?

Are the areas immediately to the south and west of the Toluca Valley likely sources for several of our "probably non-local" groups?

Are clays from the west (Toluca Valley) side of the mountain range between the Basin of Mexico and the Toluca Valley similar enough to Basin clays that they could explain some of our groups of Aztec-style ceramics that don't quite match local the very large existing reference data set for the Basin of Mexico?

Soil color and texture recording

Subsets and Samples

By Mike Smith, with comments from the peanut gallery by Angela Huster

 

After a rather involved set of phone conversations and emails among various project members trying to establish the frequency of green obsidian at the site during each phase, we realized that half our problem was the we were working with different samples. We had defined the Domestic Context Sample of lots strongly associated with dated houses several years ago, but any analyses that wanted to work with a larger sample were a free-for-all. 

Based on Mike's previous projects in Morelos, we defined five samples based on their value for the analysis of domestic artifacts and conditions. These run from the Domestic Context Sample, (now called Domestic Sample 1, or DS-1), which consists only of well-dated midden deposits, to DS-5, which is the entire sample of all excavated contexts at the site. In addition there are other samples of lots that make sense for particular analyses or materials. Most of these samples are nested; e.g., all other samples include DS-1, and DS-5 includes all other samples. Samples DS-3 and DS-4 intersect in a non-nesting fashion, however.

DS-1 (the Domestic Context Sample).   178 lots.

             This sample consists of well-dated midden deposits associated with houses. It can be subdivided into domestic components; that is, deposits from a single phase in a single unit. It was designed to provide a robust sample of materials from contexts with abundant artifacts for optimal quantification. This sample is used for:

      Household comparisons of ceramic type frequencies.

·         Ceramic type frequencies for the Aguas Celestiales chapter

It is also the source of sub-samples for particular technical analyses, including:

Ceramic attribute recording

·         Obsidian source samples

·         Ceramic petrographic samples

·         Angela’s NAA samples

DS-2 (the Extended Domestic Context Sample).  340 lots.

            This sample extends the domestic context sample to include other lots dating to the same phases at individual units. Units without representation in the domestic context sample are not included in DS-2. The advantage of a larger sample is offset by the inclusion of contexts such as fill and colluvial overburden whose association with the occupation of a house is less secure. This is used for:

·         Interhousehold comparisons of rarer items in Angela’s dissertation analyses – ground stone, copper, jewelry, whorls, and molds

DS-3 (the all-Phased sample)  1,146 lots.

            This sample consists of all lots phased to a particular period. It includes the transitional or uncertain phases (3, 5, and 44*) and phase 1 (pre-Postclassic). This is a much larger sample than DS-1 or DS-2, and its value lies in the fact that it includes the maximal number of lots that can be phased. Many of the lots have not had their ceramics classified; they are phased through stratigraphic position or associations with lots dated from their classified ceramics and/or radiocarbon dates. Its disdvantage is the inclusion of many lots whose direct association with the house occupation of each unit is more tenuous (fill, overburden, etc.). Its primary use is for comparing frequencies of rare artifacts. It is used for:

·         Rare artifact types by phase for the general project

DS-4 (the Classified Sample)  664 lots.

            This is the sample of lots whose ceramics have been classified. It has two related disadvantages compared to sample DS-2: many of the lots have not been phased; and many of the lots have only a few sherds. It is not used in any analyses.

DS-5  (all Excavated Lots).  1,668 lots.

            This is the total number of lots that were excavated. It includes many tiny lots from Alex’s soil sampling, lots from architectural excavations, and other small lots whose value for artifact analysis is minimal. It’s primary use is to generate inventories of all excavated artifacts of a given type, irrespective of phasing or quality of context. This is useful for descriptive purposes (i.e., we want to describe all of the figurines, not just the ones that fall into a more restricted sample), but not for making comparisons among units or parts of the site.

The following diagram shows the relationship among these samples.

 If anyone needs to know which samples their data fall into, please contact Angela.

Our final two hectic weeks in the lab

Here I am in the pacific port city of Guaymas, Sinaloa. After a nice norrth Mexican arrachera steak and a margarita, I'm resting up for the final day of the drive home. Whew, that was a hectic final 2 weeks in the lab. The previous post, by Angela, describes our petrographic sherd sample, one of our three massive sampling programs, all carried out during the last 2 weeks. We also picked a couple of hundred sherds for INAA analysis, and Adrian Burke picked around 250 pieces of obsidian for XRF source analysis. Each sampling program involved numerous searching through bags and boxes, cross-checking, measuring, etc. We take sampling seriously on this project, since we want the results of our technical analyses to represent various contexts, time periods, and artifact categories as well as possible. Why the rush during these 2 weeks? We needed to complete the seriation, so that we could assign the excavated deposits to phases, so that we could pick intelligent samples to monitor change through time (and other things). The seriation was not completed till just recently (I think we were too busy to post a description of this; maybe Angela or I can do this from ASU in the next few weeks).

Also, Adrian ran around looking for obsidian sources (one trip with Brad and Akiko and I to Las Palomas; and one trip just Adrian). The above photo shows Akiko and I on the hill of obsidian at Las Palomas. Brad and Akiko worked on the technological analysis of obsidian. Brad found some time to knap some of the Las Palomas obsidian (the preliminary report is, ok for bifaces, but not for blades). We got a bunch of miscellaneous cataloging done. Charles and Maria Stapleton stopped by for a day to finalize their report on censers. Kristin Nado spent several days cleaning human bone. I picked some more charcoal samples for C14 dating. Two Mexican students from the new archaeology program at UAEM, Universidad Autónoma del Estado de México, in Tenancingo (Rosario Endañú and Ali Sarabia) stopped by to help us for a while, and ended up with thesis topics. AND we reboxed the gound stone (it had been stored by provenience, and now it is stored by functional type). AND we got a number of new ceramic bags sorted. AND we pulled out ALL of the Aztec black-on-orange (even from already-analyzed bags) and re-sorted it (which had to be done before we pulled the sherd samples). All in the final 2 weeks of lab work. Wow, I'm amazed that we got it all done. Well, actually we only got 1/2 of the petrographic sample pulled. Now we could say that we ran out of time, but I'd rather say that we decided on a two-stage sampling and analytical process, so that results from the first batch will affect how we sample for the second batch. I could even come up with a citation or two to support multi-stage sampling. That sounds much better, doesn't it?