87SR/86SR IN THE LANDSCAPE, DIET AND TEETH OF A MODERN MEXICAN RURAL POPULATION: IMPLICATIONS FOR ARCHAEOLOGICAL DIETARY AND MIGRATION RECONSTRUCTIONS

In order to understand the possible causes for pervasive moderate malnutrition in the Solis Valley, Mexico, we have examined the geochemical and Sr isotopic characterisitics of the volcanic bedrock, soils, well waters, dietary components and children’s deciduous teeth of this rural region. The population is valuable to study because of a mid-1980s Mexican Government/US university nutritional study that provided detailed nutritional information about a mother’s diet during pregnancy and lactation. Tortillas, made from alkali-processed corn, constitute the dominant source of calories for a large part of the population. The Sr isotopic characteristics of tortillas and eventually of children’s deciduous teeth are strongly affected by the processing that uses Ca(OH)2 made of sintered marine limestone ("cal"). The 87Sr/86Sr ranges for the landscape components and for tortillas/cal do not overlap. Although there is a general match in 87Sr/86Sr between local well waters, soils and bedrock of this Trans-Mexican Volcanic Belt terrain in the range (0.7038 – 0.7057), foods (tortillas and cal) match late Cretaceous-early Tertiary seawater 87Sr/86Sr (0.7074 – 7080). Deciduous teeth vary quite widely from 0.7058 – 0.7077 filling the gap between the cal dominated diet and the local landscape. Using the 1980s nutrition data, we have found a strong positive correlation between 87Sr/86Sr in a child’s deciduous tooth enamel, and the percent of his/her mother’s diet supplied by tortillas during pregnancy and lactation. Because the use of sintered limestone strongly modifies the anticipated 87Sr/86Sr connection that otherwise would exist between landscape and tooth enamel, caution must be used in the study of migrations if alkali-processing with cal was used. Our findings also are useful for studies of archeological alkali processing itself, and for the possible trading of cal between population centers.