The Black San Pablo Paleosol of the Teotihuacan Valley, Mexico: Pedogenesis, Fertility, and Use in Ancient Agricultural and Urban Systems

Abstract

Although archaeologists have generally assumed that the ancient landscape in the Teotihuacan Valley was somewhat similar to the present day, recent research has documented large‐scale modification of the soil by accelerated human‐induced erosion–sedimentation processes from the pre‐Hispanic and Colonial periods up until the present. Consequently, the Formative and Classic period soil (approximately 400 B.C.–A.D. 650) is buried in most of the Teotihuacan Valley. Recent soil survey and archaeological excavation have shown that the modern soil horizon differs remarkably from the Teotihuacan soil horizon. In this paper, we present a pedogenic interpretation of the Teotihuacan paleosol referred to as the Black San Pablo Paleosol (BSPP), which contributes to the reconstruction of regional paleoenvironment and human‐induced processes. The BSPP has been identified in both natural landscapes and under Classic period Teotihuacan buildings, as well as inside the fill of the Moon Pyramid. Maize pollen and phytoliths testify to the soils use for agriculture, whereas diatoms and phytoliths indicate irrigation practices. These results are supported by soil micromorphology. The evaluation of agronomic properties of the BSPP indicates qualities suitable for agriculture; however, water infiltration is low, indicating possible problems with seasonal water saturation.