The off-site archaeological record

Archaeologist and non-archaeologists tend to think of archaeology as something that takes place at "sites". Yet, much of what humans did in the past happened away from their homes or places of work. Further, a lot of evidence about past human activities accumulated at locations far from what we would call "sites". A good example is pollen and other micro-fossil evidence for landscape changes in the past. In the photograph below, my colleagues and I are extracting a sediment core, IZT091, from a location on the coast of Guatemala that is several kilometers from any known archaeological site. The basal radiocarbon date from this core indicates that the 5.6 meters of sediment we extracted represent about 2700 years of accumulation. Pollen, phytolith, charcoal, and stable-isotope analysis of this core are currently in progress. Ultimately, these analyses will provide a 2700-year history of changes in forest cover, including human-induced changes, upstream from this location.

LiDAR imagery from Pacific coastal Soconusco

The first image below is a Google Earth image showing part of the area on which fieldwork over the next several years will focus. This area is just west of the Rio Cahuacan, which can be seen at the right side of the first two images. The mouth of the Rio Cahuacan is about 13.7 km west of the mouth of the Rio Suchiate, which is the international border between Mexico and Guatemala. The red polygons are areas indicated as "sites" in the Mexican (INAH) site records. Markers labeled "DB" are also from the INAH records. The other markers are mounds that my colleagues and I have visited over the past several years.

The next image is the same area from Google Earth, but with minimally processed LiDAR images overlain. The labeled white spots on the LiDAR imagery are archaeological mounds, and the others, clearly, are mounds as well, just ones that haven't been checked yet on the ground.

The final image, below, zooms in on the area with the visited archaeological mounds and uses hillshade to highlight the mounds that show up on the LiDAR imagery. The blue dots indicates mounds that we have visited, the large one at the very top being "Conq1" (Conquista-1) from the previous images.

NSF award for work in the estuarine zone of Pacific coastal Soconusco

I recently learned that a NSF proposal submitted last December for work in coastal Soconusco was successful. Following is the public abstract for the award:


The tropical coasts of Mesoamerica are lined with mangrove forests and estuaries that, while rich in many food resources, are of little use for agricultural production. As a result, once Mesoamerican people (forerunners of the Aztec, Maya, and other Native American groups of Mexico and Central America) became fully committed to agricultural subsistence, probably during the Middle Formative period (~800 - 400 BC), human habitation shifted away from the coasts. The coastal margins continued to be utilized for hunting, fishing, and shellfish collecting, but increasingly over time as well for industrial production. Salt extraction is one well-documented activity, and recent research has indicated that large-scale ceramic production was another such activity. To date, there have been very few systematic investigations of these coastal Mesoamerican industrial sites. There is some urgency to initiate such studies because sea-level rise and environmental degradation threaten to submerge or destroy coastal sites over the coming few decades.

The National Science Foundation has provided funds to support a three-year effort to document archaeological remains on one section of the Mesoamerican coast, the far-southern Pacific coast of Chiapas, Mexico, a region known as Soconusco. One fundamental issue that this NSF project will address is whether the boom and bust cycles posited for Soconusco are real or whether they may be artifacts of the coarseness of the existing chronological framework. By investing heavily in chronometric analysis (radiocarbon and luminescence dating) this project will dramatically improve chronological resolution. If demographic change still appears to be abrupt and cyclical once a better chronological framework is available, then it becomes sensible to begin evaluating possible causes of collapses, population explosions, and prolonged abandonments. Unlike the cases discussed by Jared Diamond in Collapse, all of the instances of 'collapse' and recovery listed above took place in a single region, so geography is held constant, and other possible causes of demographic change, such as climatic downturns or amelioration, population movements, local political events, and organizational or technological innovation, can be examined without the confounding effect of geographic variability. 

Not only did prehistoric Soconusco people use the mangrove zone for industrial activities, leaving an abundance of archaeological remains, the zone itself acts as a catch basin for plant parts and charcoal brought down rivers and streams or blown in from the coastal plain. This means that changes in vegetation cover in the coastal-plain agricultural zone are recorded in sediments of the mangrove zone. Thus, while mangrove-zone archaeological remains document industrial activities that people engaged in away from their inland agricultural villages, the sedimentary record documents upstream land clearance, which correlates with population levels on the coastal plain. The archaeological and geo-archaeological research recently funded by NSF will sample and analyze these complementary historical records. 

According to current archaeological understanding, the records targeted for investigation on this project were shaped by momentous changes that swept across Soconusco at various times during prehistory and history: 

- The region was a center of pre-Maya sculptural art, but the sculptors abruptly closed up shop around 2000 years ago, and much of the coastal plain seems to have been abandoned. 

- Emissaries or militarists from the highland Mexican empire of Teotihuacan arrived around AD 400, apparently initiating a period of sustained population growth that lasted at least through Terminal Classic period (~AD 1000). 

- During the Terminal Classic, potters of the estuary zone produced Plumbate, the most technologically sophisticated and widely traded pottery every made in Mesoamerica. 

- Population appears to have collapsed again around AD 1100.

- Late Prehistoric population resurgence began around AD 1250. 

- At the time of the Spanish conquest (AD 1521), Soconusco was the most distant province of the Aztec empire and paid tribute to the rulers of Tenochtitlan (Mexico City).

- Population again plummeted soon after the conquest, as introduced European diseases decimated the population, a collapse from which it did not recover until the early 20th century. 

The project will provide research opportunities for MA students at several California State Universities in the Los Angeles area and for Ph.D. students at Washington State University, SUNY-Albany, and UCLA.

Murata (2011) dissertation.

Satoru Murata just defended a dissertation at Boston University that describes his work at a salt- and ceramic-production site in Belize. It's a great piece of work, with results that are very pertinent to the Pacific coastal southern Chiapas sites discussed in an earlier post. You can access his dissertation at the link below.

http://bu.academia.edu/SatoruMurata/Papers/377475/Maya_Salters_Maya_Potters_The_Archaeology_of_Multicrafting_on_Non-residential_Mounds_at_Wits_Cah_Akal_Belize

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.

Introduction

Stephen Weiner's book, Microarchaeology: Beyond the Visible Archaeological Record, is the inspiration for my title. Weiner’s premise is that many of the most informative properties of the archaeological record are inaccessible to our senses and require instrumental assistance in order to be perceived or measured. This "microscopic record" includes microscopic artifacts as well as properties of macro-remains that are only observable microscopically. Weiner points out, following the physicist Feynman, that this microscopic record is vast, since there are seven orders of magnitude between the millimeter scale and the scale of atoms. Informative measurements on this sub-visible (but vast) record can be made via microscopy, infrared (IR) spectroscopy, elemental analysis, x-ray diffraction, isotopic analysis, residue analysis, DNA analysis, and other techniques.

My main purpose in starting this blog is to have a place to post notes and news about archaeological research I will be doing on the Pacific coast of Chiapas Mexico, a region also known as Soconusco, over the next several years. The project is a bit different from many archaeology projects in that it will emphasize instrumental measurements both in the field and in the lab to eliminate the need for invasive archaeological sampling. In the field, I'll use ground-penetrating radar and magnetometry to identify anomalies for sampling. I'll take subsurface soil samples with a split-core sampler, and then use x-ray fluorescence to characterize vertical and horizontal geochemical variation. The portable-XRF will be configured to optimize for phosphorus, which is a good indicator of high organics, like middens, and calcium, which is a good indicator of wood ash, such as would be produced by kitchen fires, pottery firing, and so on.  

I'll write more about the purposes of the project and the various analyses planned later on. Ultimately, I'll be posting geophysical survey imagery, photos, and other kinds of raw data.