ANALYSIS OF ADOBE WALL COMPOSITION AT THE CHAVES-HUMMINGBIRD SITE, NM BY DIFFUSE REFLECTANCE SPECTROPHOTOMETRY: IMPLICATIONS FOR CONSTRUCTION

Adobe wall samples from Chaves-Hummingbird Pueblo, an ancestral Pueblo village located ~20 miles west of Albuquerque, N.M. were analyzed with a diffuse reflectance spectrophotometer from the near ultraviolet through the visible and into the near infrared region of the electromagnetic spectrum, that is, from 250 - 850 nm. The walls were constructed with native clay-rich soils some time between approximately 1250 - 1450 A.D. Factor analysis of the spectral data indicates three dominant factors explaining 72.5% of the cumulative variance. In terms of composition the three factors represent samples in which the spectral signal is dominated by (1) smectite clay, (2) organic matter, and (3) iron oxides, especially goethite. Maps of factor scores indicate that each factor spatially clusters in distinct architectural areas of the roomblock. The smectite factor dominates in northeastern walls, the organic matter factor is predominant in west-central walls, and the iron oxide factor is most important in the north-central region. The southern portion of the roomblock walls contain a mixture of all three factors. The three factors and distinct areas of the roomblock where they predominate may be due to one or more causes. First, the factors may relate to the use of two or more quarries for the adobe. Second, there may be sufficient compositional variation across or within depositional strata in the adobe quarries to account for the factors. Third, the factors may relate to different "recipes" utilized by various residential groups within the pueblo. Initial archaeological indications are that some of the occupants of the settlement may have migrated into the area during the main occupation phase at Chaves-Hummingbird Pueblo. Finally, the factors may be due to the combination of two or more of these conditions or processes.