|
|
While excavations in and around El Coyote’s main plaza have been useful for determining the kinds of material culture employed in the activities performed therein, the precise locations of activities remain unknown since artifact distributions indicate that plaza debris was moved to its margins and, in some cases, probably transported to the middens outside its northwest and northeast corners. In order to better understand activity distributions in the plaza, I sampled and chemically characterized soils for available phosphates and other anthropogenic compounds.
It has long been recognized that concentrations of phosphorus and other major and minor elements at archaeological sites can be linked with food preparation and consumption, among other cultural activities involving organic substances. The underlying premise is that certain chemical compounds are associated with human activities, such as phosphates with middens, sodium and potassium compounds with hearths, and iron and copper oxides with painted buildings. Since these compounds are rapidly fixed to the mineral surfaces of calcareous sediments, they tend to remain stable in soils for very long periods in the form of adsorbed and complexed ions on clay surfaces, and as insoluble oxides, sulfides, and carbonates, all of which can be chemically detected. A total of 250 soils were sampled from surface contexts in the plaza and on the monumental stairway, along with 280 other samples taken from contemporaneous surfaces outside the plaza. All samples were transported to the Laboratory for Archaeological Chemistry at the University of Wisconsin-Madison where they were analyzed for phosphates and major and minor elements using the laboratory procedures developed by James Burton and Arleyn Simon and by William Middleton and T. Douglas Price. For this technique, each sample is air-dried, sieved in a 2 sq. mm mesh plastic screen to remove organic debris and clastic materials larger than sand, and pulverized with a Coors porcelain mortar. A .2 g portion is taken from each sample and mixed with 20 mL of dilute 1 N HCl and shaken vigorously. The resultant solution is then allowed to sit for two weeks at room temperature, after which it is filtered using ashless filter paper. The concentrations of aluminum (Al), barium (Ba), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), sodium (Na), phosphorus (P), strontium (Sr), zinc (Zn), manganese (Mn), and titanium (Ti) were determined using an ARL 3520 OES inductively coupled plasma atomic emission spectrometer. The results are reported in parts per million (ppm) of the element and were converted subsequently to base 10 logarithms for comparability.
| 
| 
|