THE INFLUENCE OF MESOAMERICAN OBSIDIAN MINING ON THE SOIL FORMATION OF TECHNOSOLS: 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 and folic diagnostic horizons, and abundant biogenic features, and were classified as Spolic Technosols (Loamic, Hyperartefactic). 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 Coarsic Skeletic Sapric Hemic Fibric Folic Histosol (Hypertechnic); however, we propose reclassification as Folic Technosol to better reflect its technogenic origin and aerobic pedogenesis. Natural reference soils were classified as Umbrisol and Regosol. Micromorphological evidence demonstrates that soil biota (roots, mesofauna, fungi) play a crucial role in transforming technogenic deposits into functional soils in temperate forest landscapes. We conclude that pre-Hispanic obsidian mining generated Technosols in which the degree of soil development directly indicates the time elapsed since mining cessation and disturbance intensity. 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.

中美洲前西班牙殖民时期的黑曜石采矿活动，是墨西哥中部高地最早且分布最广泛的人为景观改造活动之一，但其对土壤发生（pedogenesis）与技术土（Technosol）形成的长期影响仍未得到充分阐释。位于伊达尔戈州的拉斯纳瓦哈斯山（Cerro de Las Navajas）产出的绿金色黑曜石矿点，在超过1600年的时间里先后被特奥蒂瓦坎、托尔特克与阿兹特克文明持续开采，为我们沿山坡梯度研究人为土壤演化提供了独特契机。我们针对5份具有不同开采历史的土壤剖面以及2份自然对照土壤，开展了形态学、物理学、化学与微形态学分析。受特奥蒂瓦坎时期较早、强度较低的采矿活动影响的上坡与中坡位土壤，发育出具有良好团聚体结构、暗沃诊断表层（umbric diagnostic horizon）与松软诊断表层（folic diagnostic horizon）以及丰富生物成因特征的A-B-C土层构型，被归类为壤质高人工化剥离型技术土（Spolic Technosols, Loamic, Hyperartefactic）。相较而言，受阿兹特克时期高强度深层采矿活动影响的下坡位土壤仅呈现初始发育特征（O-C或CA-C土层构型），具有无团聚体微结构（apedal microstructures）并伴随大量新鲜黑曜石碎屑。其中1份剖面夹有40厘米厚的有机层与黑曜石薄片，被归类为高人工化粗骨性纤维半腐殖松软有机土（Coarsic Skeletic Sapric Hemic Fibric Folic Histosol (Hypertechnic)）；但我们建议将其重新归类为松软表层技术土（Folic Technosol），以更准确反映其人工成因与有氧土壤发生过程。自然对照土壤被归类为暗沃土（Umbrisol）与初育土（Regosol）。微形态学证据表明，土壤生物群落（soil biota）、根系、中型土壤动物（mesofauna）与真菌在温带森林景观中将人工沉积物转化为功能性土壤的过程中发挥着关键作用。本研究结论显示，前西班牙殖民时期的黑曜石采矿活动催生了技术土，其土壤发育程度直接反映了采矿停止后的时间跨度与扰动强度。本研究证实，技术土可作为人类历史的土壤学档案，且土壤生物群落在温带森林景观中将人工沉积物转化为功能性土壤的过程中同样发挥着关键作用。