Dispatches from the Field: Art Joyce, July 2008
I spent the last two months in the southern Mexican states of Oaxaca and Guerrero carrying out field research on environmental change over the past 10,000 years as part of a larger study of the history of human impact on the ecology of the Río Verde drainage basin. The research included sediment cores extracted from ponds and estuaries for pollen and isotopic studies of past plant communities, geomorphological studies of erosion, phytolith studies of past vegetation, soil isotope studies of climatic and vegetation change, and studies of landscape features using satellite imagery.
The study was funded by a CU Innovative Seed Grant and by a Research Grant from NASA. Collaborators included scholars from the Mexican Centro de Investigaciones y Estudios Superiores en Antropología Social (CIESAS), Cornell University, Richard Stockton College of New Jersey (RSC), Rochester Institute of Technology (RIT), San Diego State University (SDSU), and the University of Utah.
The project has been very successful. We spent the first half of the project coring ponds and estuaries for pollen and isotope studies. The first couple of weeks were on the Oaxaca coast where daytime temperatures often reached 110F. The work included a day-long hike into the “fire swamp” carrying our coring equipment and spending hours struggling through the thorny scrub, heat, and bugs.
We often had to wade through deep irrigation canals, which wasn’t so bad until we spoke with a local landowner who was shooting at a crocodile that had been eating his goats. The strong afternoon winds played havoc with our sampling platform, but we were able to get deep cores from several ponds in the region.
The coring team of Michelle Goman and Willie Guerra from Cornell along with Pepe Aguilar from SDSU also worked out some kinks in the sampling procedure. Project geomorphologists Ray Mueller and Lucia Pou (RSC) carried out a geological survey of ancient river deposits. While coring on the coast I also worked with CU alum Stacy Barber who is now Assistant Professor at the University of Central Florida on a Ground Penetrating Radar Study of the ceremonial center of the ancient city of Río Viejo. I also assisted graduate students Michelle Butler (UC-Riverside) and Guy Hepp (Florida State) on investigating possible Ph.D. projects.
In late May we travelled to the Mixtec Highlands of western Oaxaca and eastern Guerrero for more coring studies. This part of the project was a real road trip since we were investigating possible sampling locations over a huge area based on evidence from topographic maps and aerial photographs. We spent time in the towns of Putla, Chalcatongo, Huamuxtitlan, and Tamazulapan. Some days we drove for over eight hours through treacherous mountain roads. We stayed in some pretty bad hotels and ate a lot of tortillas, eggs, and chicken in little restaurants along the way. We spoke with dozens of local officials to obtain permission for the research and were greeted with support and interest.
We spent time in some amazing places like the Mixtec town of Chalcatongo home of a sacred cave where the Mixtecs kept the mummy bundles of their prehispanic kings and queens until the Spanish destroyed them as idols. Chalcatongo is also over 8000’ in elevation and morning temperatures were sometimes in the 40s. We had a few rainy days where we almost froze on the sampling platform, but we ended up with several deep cores from two sinkhole ponds. One of the cores was almost 6 meters deep and exhibited banding, which might be annual varves possibly giving us the ability to look at climatic and vegetation change on an annual basis.
We often left the field in the evening wet and muddy hoping to get to a local restaurant with a wood burning oven used to make pizza so we could sit as close to the oven as possible and try to warm up. We also extracted another deep core from a pond at Huamuxtitlan in the state of Guerrero. The pond sat at the base of the 1000’ cliff of a gypsum mountain. In Huamuxtitlan we were kindly assisted by Gerardo Gutierrez (CIESAS) who has worked in the area for over a decade and who gave a colloquium in the department last semester. Gerardo took us into some very remote areas along the border of Oaxaca and Guerrero looking for possible sampling locations.
The second month of the field season was spent in the Nochixtlán Valley of Oaxaca where I have carried out geoarchaeological research with Ray Mueller for the past 20 years.
This field season we were joined by Naomi Levin (Utah) and Bill Middleton (RIT). Ray and Lucia continued the research on sediments exposed in deep river cuts in the region to examine periods of erosion possibly triggered by ancient agriculture or climatic change.
Naomi began a study of soil isotopes, probably the first research of its kind in Mexico, to investigate climatic and vegetation change in the region. She also took phytolith samples, which will be examined by Bill to track changing plant communities associated with the buried soils.
Bill and his students also took modern sediment and plant samples to create a phytolith reference collection.
The sedimentological and isotope studies of soils and sediments exposed in the river cuts were both fascinating and at times a little frightening. Some of the river cuts are over 60’ deep and required the use of a rope ladder or climbing gear. Fortunately, Alex Borejsza from the Universidad Nacional Autónoma de México stopped in to visit for a few days and brought his climbing gear, which helped us tackle some of the deepest river cuts. While repelling off a 60’ deep exposure was certainly scary, the most daunting part of the time in Nochixtlán was our hotel with its irregular water availability, moldy walls, and bad smells.
We spent some time with CU grad student Michelle Trogdon who was carrying out a study of ancient agricultural terraces exposed in the river cuts. I also spent a fascinating day with Jamie Forde at Achiutla where he plans to conduct Ph.D. research on the contact period.
We are now back in Oaxaca City enjoying the easy life here and organizing samples for our return to the U.S. The field project was a great success and now comes years of laboratory analyses.