Material diversity of the littoral zone mounds of far-southern Chiapas, Mexico

From early February through early March, 2011, I stayed with a field team doing archaeological survey on the Pacific-coastal plain in far-southern Chiapas, Mexico. The team is led by Robert Rosenswig, from the SUNY-Albany. Their goal is to cover a large area of the coastal plain systematically, in contrast to the haphazard surveys that have been carried out in the past. Rosenswig's dissertation research was one of the first truly systematic surveys.

During the week of February 26 through March 4, Rob's systematic coastal plain survey was on hold, which gave me, Dan Seinfeld, and several of Rob's students the opportunity to poke around in the mangrove swamp, to try to augment the inventory of sites from that zone. Dan was mainly interested in identifying Archaic-period shell middens, and my main purpose was to get started on the Classic -- Modern period study I have been planning for the last several years. Although we failed to find shell-midden sites (there are still some additional leads to check out), the week was wildly successful in terms of numbers and diversity of archaeological contexts documented.

In the image above, all of the red pluses within the mangroves (outlined in lime green) are new mounds identified during our survey (a total of 28). The yellow push-pins are archaeological contexts that I had visited previously. The red polygons are areas designated as "sites" in the INAH (Instituto Nacional de Antropologia e Historia) registry of archaeological sites in Mexico. The yellow rectangle is the area I hope to have covered by airborne LiDAR sometime in the near future. The purple polygon is the area Rob Rosenswig surveyed during his dissertation research, in 2002 - 2003, I believe.

Based on surface observations, most of the contexts we visited are Late Classic. Ceramics tend to be eroded, and to include large vessels as well as "rolling pins," which I believe were used in salt production. Plumbate is a dominant ceramic type, probably even moreso than one might suspect at first glance because the diagnostic surface is eroded away on many of the surface sherds that are visible at the bases of the mounds. There are also very large, crude, ceramics in nearly whole condition on the tops of many of the mounds. I believe these may be remains of historic salt-production activities.

Beyond the obvious Late Classic and Historic remains, I was a bit surprised to see Early Classic diagnostics (a specific rim form that we call "Nahualate ware" in Guatemala) as well as Late Postclassic diagnostics (collanders and strap handles). In addition, Early Postclassic Tohil Plumbate is present, and some of the large domestic jar rims have a very distinctive "pseudo-thickened" lip whose only other occurrence I am aware of is on Tohil Plumbate jars. So our survey suggests the possibiliity that the littoral zone of this region has been used intensively from Early Classic through modern times (roughly the past 2000 years).

The zone was used much earlier, too. One day when I wasn't able to join them, Dan and the crew slogged through the swamp to a large circular feature visible on Google Earth about 600 meters north of the beach town of El Gancho. The feature proved to be a 10+ meter high mound with abundant Early Formative ceramics and lots of oyster shell. (Oysters, by the way, are still abundant in the estuary, and are very tasty right out of the water, as Teo, one of our guides, demonstrated to us.)

Beyond the chronological diversity, there is also more functional diversity than I anticipated. Although obsidian is sparse, some of the Late Classic/Early Postclassic sites had blades that probably originate at the Ixtepeque source, in southeastern Guatemala. Castano-1, the Early Formative site, had a flake that appears to be from El Chayal, near Guatemala City. One of the Late Classic/Early Postclassic mounds also had two fragments from very well made, basalt metates. Shellfish remains were observed both on the Classic through Historic sites and at the Early Formative sites. And while the ceramic assemblages appear to be dominated by salt-production implements, nice serving vessels, mainly Plumbate, are well represented as well. The abundant amorphous fired clay present on virtually all mounds also may not be solely related to salt production; it may represent remains from Plumbate production, as I have suggested in publications. So yes, Classic period through modern people have been producing salt in the estuary zone, but they have also been doing other domestic activities and possibly producing pottery.

Our week's worth of work only scratches the surface. Below is a blow-up view of an area we explored on March 3, 2011, showing the seven archaeological mounds we visited (PIN1 - PIN7). Notice about 200 meters west of PIN7 there is a complex of two mounds, one of which has either canals or causeways leading to it. This is most likely some kind of historic installation, but darn, I wish I had had one more day to check it out!

How does all this macro-archaeology fit into a blog on "microarchaeology"? Well, the macro-observations provide some hypotheses, such as:

• the estuary zone has been used somewhat intensively for the past 2000 years
• people using the zone produced (and presumably exported) salt
• people using the zone also lived there and carried out domestica activities
• people may have produced pottery there (there's more basis for this hypothesis than I've related here)

Microarchaeology comes in because both the artifacts and their matrix can be characterized in a variety of ways that bear on the validity of these hypotheses. For instance, variability in phosphorus can identify areas of organic debris from middens, whereas high-calcium concretions might represent areas of wood-ash deposition that became wet, or, alternatively shell. Phytoliths from the sediments also bear on these questionos.

I'll end with a photograph taken by Dan Seinfeld that shows the matrix and some of the ceramic artifacts at the base of PIN4. Here the macro remains (Plumbate, a Late Postclassic collander) suggest chronological and functional hypotheses that can be tested through a microarchaeological approach both to the ceramics themselves and to the bright red matrix in which they are embedded.