SAA symposium

Microarchaeology will certainly be well represented at the upcoming SAA meetings in Sacramento. For instance, a symposium on "New Perspectives on the Archaic Period of Coastal Chiapas, Mexico" features papers on analysis of pollen, phytoliths, and chemistry of archaeological sediments as well as Bayesian analysis of radiocarbon dates and more. The symposium abstract and individual abstracts follow.

Working Draft of Proposed Symposium for the SAAs in 2011

March 30-April 2, 2011

Symposium Title:  New Perspectives on the Archaic Period of Coastal Chiapas, Mexico

Organizer: BV

Moderator: Heather Thakar

Symposium Abstract

Recent archaeological, paleobotanical and geoarchaeological research on the Chiapas coast provides new insights about the lifeways of Archaic Period people (7500-3500 yrs BP). We now detect changes in fishing practices and an earlier onset of farming.  We muster multiple lines of evidence to understand the purpose of unusual superimposed floors at one shell mound.  Using spatial data from inscribed features, chemical elements, phytoliths, chipped stone, densities of small bones and color differences in the clay matrix, we infer past activities carried out on the floor surfaces. Proposed activities include drying aquatic resources, food consumption and pickup dice games.

The Site that Keeps on Giving: Thirty plus Years of Research at Tlacuachero

Barbara Voorhies

University of California, Santa Barbara

This paper presents an introduction to the symposium including background about the Tlacuachero shell mound, its research history, and the most recent focus on the enigmatic superimposed clay surfaces underlying one area of the site.  The paper summarizes previous evidence for both stability and diachronic change in ecological adaptation during Late Archaic Period site occupation as a backdrop for new research reported in the symposium.

Bayesian Analysis of AMS Radiocarbon Dates from a Prehistoric Mexican Shellmound

Culleton, B.J., Kennett, D.J., Voorhies, B. and Southon, J.R.

We establish a high precision AMS radiocarbon chronology for the Tlacuachero shellmound (Mexico) within a Bayesian statistical framework. Carbonized twigs were sequentially selected from well-defined stratigraphic contexts based on iterative improvements to a probabilistic chronological model. Analytical error for these measurements is ±15-20 ¹⁴C years. This greater precision and the absence of stratigraphic reversals eclipses previous radiocarbon work at Tlacuachero. We develop a chronological framework for a sequence of three clay floors (4960-4270 cal BP) and determine that the bedded shell that dominates these deposits accumulated rapidly during two episodes from 5050-4840 cal BP (2m) and 4380-4230 cal BP (3.5m).

Pre-Pottery Farmers on the Pacific Coast of Southwest Mexico

Douglas J. Kennett, Dolores R. Piperno, John G. Jones, Hector Neff, Barbara Voorhies, Megan Walsh and Brendan Culleton

We present paleoecological data from sediment cores taken along the Pacific coast of southwest Mexico in close proximity to Archaic Period archaeological sites. Burned maize phytoliths first appear in these sedimentary records at 6,500 cal BP in association with macroscopic charcoal and forest disturbance plant taxa. Periodic burning and forest disturbance, consistent with farming activities, is also evident in the macroscopic charcoal record between 6,500 and 4,700 cal BP. These data indicate that people were slash and burn farming during the Archaic Period prior to the adoption of pottery and the proliferation of Early Formative Period villages after ~3,800 cal BP.

Archaic Period Vertebrate Exploitation at Tlacuachero, Chiapas

Thomas A. Wake and co-author

Recent excavations at the Pacific coastal Archaic Period shell midden site of Tlacuachero, Chiapas, have recovered a diverse array of vertebrate faunal remains. Fish remains dominate these samples that also include reptiles, birds and mammals. Several of the bone samples are associated with constructed surfaces. Distribution of vertebrate remains across these surfaces along with changing fishing strategies through time are examined.  Implications for resource depression or stability and regional resource use patterns are discussed.

If Floors Could Talk: Investigation of Clay Floors at the Tlacuachero Shell Mound

H.B. Thakar

Recent research at the Tlacuachero shell mound investigated a series of deeply buried constructed clay floors positioned under the mound summit. This work confirmed that these floors are marked with postholes and other features. We exposed large areas of the two uppermost floors, mapped their features, and sampled their surfaces using random and non-random methods. This paper presents the field and laboratory methods used for the collection of samples from the constructed surfaces as well as the laboratory methods used to study the matrix color and fish bone density. Results of these two analyses reveal interesting and surprisingly similar patterns. 

Early Use of Chipped Stone at the Tlacuachero Site, Soconusco, Chiapas

Elizabeth H. Paris

At Late Archaic period shell mound sites along the Pacific Coast of Chiapas such as Tlacuachero, chipped stone artifacts were extraordinarily scarce.  Most of these artifacts are bipolar percussion flakes produced from small ignimbrite nodules from the nearby Tajumulco source, and are particularly associated with clay floor deposits stratified within bedded shell deposits.  Some flakes possess edge damage consistent with use as microdrills, and may have been used to produce fishhooks or other artifacts.  Such uses of chipped stone technology would be consistent with the role of the site as a seasonal fishing and shellfish processing site for lagoonal resources.

Spatial Analysis of Phytoliths from an Archaic Shell Mound in Coastal

Chiapas

Doug Drake and John G. Jones

A detailed analysis of phytoliths from the Tlacuachero shell mound is revealing information on prehistoric plant use and human activity. Samples collected from a prepared floor in a gridded pattern in 1m increments along with corresponding feature samples, are revealing distribution patterns of past plant use. These patterns appear to document the presence of ancient architecture on the prepared surface, and may represent thatched structures and/or drying racks. The presence of potential economic phytolith types including grasses, palms, and Heliconia may be significant, and forest taxa are also represented in the assemblages.

Elemental analysis of the Tlacuachero floors

Hector Neff and Barbara Voorhies

Sediment samples from two floors at Tlacuachero were analyzed by x-ray fluorescence and laser ablation ICP-MS on the expectation that patterns of elemental enrichment and depletion might suggest the nature and locations of activities when each floor was a living surface. Dried fish, shrimp, and corn meal were analyzed to derive expectations about how food processing might affect the elemental signature. Highly enriched phosphorus in the floor samples confirms that animal and/or plant tissues were processed on the floor and contributed to the elemental signature. Patterns of enrichment and dilution of phosphorus and other elements indicate locations where these activities were concentrated.

BV Discussant:  Overview of floor data (including dice game proposal).  This “discussion” would summarize the various lines of data from floor samples.

John E. Clark Discussant

            John will explain how we got everything wrong.  Confirmed participation.

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.