The influence of Mesoamerican obsidian mining on Technosols formation: A case study in las Navajas, Hidalgo, Mexico

Pre-Hispanic obsidian mining in Mesoamerica was one of the earliest and most widespread anthropogenic landscape modifications in the Mexican Central Highlands, yet its long-term impact on pedogenesis and Technosol formation remains poorly understood. The green‑gold obsidian deposit at Cerro de Las Navajas (Hidalgo), exploited successively by the Teotihuacan, Toltec, and Aztec cultures over >1600 years, offers a unique opportunity to investigate anthropogenic soil evolution along a hillslope. We evaluated five soil profiles with different exploitation histories and two natural reference soils using morphological, physical, chemical, and micromorphological analyses. Soils on upper and middle slopes affected by older, less intensive Teotihuacan-period mining exhibited A-B-C horizons with well-developed aggregates, umbric, folic, and cambic diagnostic horizons, and abundant biogenic features, and were classified as Spolic Technosols. In contrast, lower-slope soils impacted by intensive Aztec-period deep mining showed incipient development (O C or CA-C horizons), apedal microstructures, and abundant fresh obsidian fragments. One profile with 40 cm of organic layers interbedded with obsidian flakes was classified as Skeletic Folic Histosol. Natural reference soils were classified as Vitric Andosol or Vitric Umbric Andosol. Micromorphological evidence demonstrates that soil biota (roots, mesofauna, fungi) play a crucial role in transforming technogenic deposits into functional soils in temperate forest landscapes. The main conclusion is that Technosols reflect the intensity, duration, microrelief, and extraction techniques employed by the Teotihuacan, Toltec, and Aztec cultures. Beyond the local context of Cerro de Las Navajas, this study demonstrates that Technosols can serve as pedological archives of human history, and that soil biota plays a crucial role in transforming technogenic deposits into functional soils in temperate forest landscapes.