Terraces and landscape in Mixteca Alta, Oaxaca, Mexico: Micromorphological indicators

In the semi-arid Mixteca Alta, Mexico, complex societies developed sophisticated terrace systems to control erosion and improve rain-fed agriculture. Knowledge regarding the agricultural systems has been crucial in understanding landscape construction through cultivation and social complexity. In this study six sequences on terrace systems were investigated. The samples were analyzed for bulk chemical, textural and micromorphological observations. Soils developed on terraces of the Yanhuitlán river (sequences Y04 and Y05) were dated, respectively, 5,300, 2,700 and 1,100 cal BP, suggesting a possible anthropic use since the early Formative period. These soils are composed of microstratified fine sediments of local origin, reflecting low energy during their deposition; they are weakly structured and developed in anoxic conditions due to saturation during terrace flooding. However, in these soils, a mixture of silt particles and charcoal fragments suggests the influence of anthropic use. On the other hand, sequences Y01 and Y02 are Pleistocene soils developed in an anoxic environment of a swampy landscape; their vertic properties may be related to dry seasonal periods. Knowledge of landscape genesis contributes to the assessment of anthropic impact in the area.