Determining the Function of Constructed Activity Surfaces at the Tlacuachero Shell Mound

    In 2009 I returned to the Tlacuachero shell mound on the outer coast of Chiapas, Mexico, in order to investigate a series of clay floors/surfaces that lie under the mound summit within the bedded shell deposits.  These floors are deeply buried and difficult to access but their combined extent is approximately 900 m2. Previous work had revealed that artifacts were notably scarce on the floor surfaces but that postholes, rock impressions, and figures outlined by small holes occurred on their upper surfaces. My previous work led me to conclude that these floors were not constructed as part of the infrastructure of permanent residences, which made it imperative to consider alternative explanations. 

One hypothetical alternative model is that the floors were constructed in connection with ceremonial activities that required both a smooth surface and a large area to accommodate a large gathering of people. Such periodic aggregations are common for mobile peoples who spend much of their time in small groups.  Despite the attractiveness of this idea, at present there is little evidence in support of it. 

Another hypothetical model is that the floors represent a variation on the function accounting for the build up of the bedded shell layers that comprise the main deposits dating to the Late Archaic Period at this and other similar neighboring sites.  My interpretation is that these coastal shell mounds formed as the result of processing resources from nearby lagoons, particularly marsh clams and fish. The floors and associated features were constructed during an interval when greater investment was made in the site infrastructure compared to before or after.  In order to assess this idea and to try to define more precisely what activities were carried out on the floor surfaces, the archaeological team collected floor samples using random and non-random sampling strategies.  These samples will be analyzed for color, type and density or phytoliths, density of small bones, and concentrations of selected chemical elements with the goal being the identification of spatial patterns that will reveal activity loci.  The phytoliths are being studied by Douglas Drake and John Jones at Washington State University.  Hector Neff, Cal State-Long Beach, is conducting the chemical studies and Douglas J. Kennett and Brendan Culleton, of the University of Oregon, Eugene, have conducted the analyses to date the various deposits at the site. 

The research was funded by the National Geographic Society and UCMexus.

Upper Surface of Floor 1 being readied for final photographs