Soil modification in the manufacturing process of Mesoamerican earthen architecture

This paper presents a micromorphological analysis of a sample series from three Mesoamerican earthen architecture sites. It compares a soil, a sample from a construction fill and a sample of a soil mixture used for mud-brick and facing, resulting from different manufacturing steps. The purpose is to identify the soil features that remain and those that are transformed in the process. This is of interest both to geologists, who encounter anthropically modified soils, and archaeologists interested in understanding the provenance of the raw materials and the manufacturing processes. In contrast to previous research based predominantly on earthen architecture from Europe and the Near East, this study is the first comparative analysis of Mesoamerican sites, where earthen construction developed independently from the Old World, using volcanic soils developed in a range of tropical environments. The results show that similar building techniques existed in different environments, that the non-expansive clays and fine fraction derived from volcanic deposits may have presented advantages for construction, while some features reflect the addition of mineral or vegetal temper to improve the mechanical properties of some soils.