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Paleosol sequences of the Nevado de Toluca volcano (NTV) preserve a detailed record of late Quaternary environmental change. In fact, some studies have been used the NTV paleosols to interpret paleoenvironmental conditions, however some uncertainties still remain concerning their stratigraphic position and correlation. In this paper, we present the results of the NTV pedostratigraphy by using different paleosol units and based on present day tephrostratigraphy. We recognized eight Pleistocene paleosols, labeled PT0–PT7 which cover the 100,000–10,000 yr BP interval. These paleosols are located in four exposures: Arroyo La Ciervita, in the northern flank of the volcano, Zacango, in the northeast, and San Pedro Tlanisco and Barranca Cieneguilla, in the eastern part. The younger five paleosols correspond to different intergrades of Andosols (PT0–PT4) while the older sequence consists of three well developed Luvisols (PT5–PT7). All Andosols have humic horizons allowing radiocarbon dating. PT0 and PT1 were formed at the end of the Pleistocene and correlate with the oxygen isotope stage (OIS) 1 and to the middle-late OIS-2, respectively; the time for PT2 formation corresponds to the end of OIS- 3 and the beginning of OIS-2, PT3 to the OIS-3, and PT4 to the OIS-4. PT5–PT7 have not yet been dated, but we correlate them with the OIS-5a and 5b. A more strongly developed paleosol (PT1) was formed during the Last Glacial Maximum (18,000 yr BP) in comparison with other paleosol sequences where weakly developed paleosols were reported or even no soil formation was achieved in this period. We conclude that during late Pleistocene to Holocene, OIS 5 to 1, paleosol sequences of the Nevado de Toluca provide good environmental resolution, similar to or even higher than loess-paleosol sequences, although stratigraphic correlation with other paleoenvironmental records is more difficult because of the heterogeneity of volcanic sediments.

The Teotihuacan valley, located in the northeastern sector of the basin of Mexico, was settled by approximately 1,100 BC. The first and largest prehistoric city in the Americas developed here in AD 350–550, reaching a population of around 125,000. The demise of the Teotihuacan state is now generally believed to have culminated between AD 600–650. Causes are attributed to global climate change, environmental degradation, economic and/or political upheaval, but no direct evidence has ever been presented to support these hypotheses. The study of paleosols contributes to the understanding of the environmental conditions that prevailed in the Teotihuacan region in order to better comprehend their potential relationship to cultural and economic events in the prehistoric past. The distribution of soils in the region is directly associated with relief. Profiles at Cerro Gordo (3,050 m a.s.l.) and Cerro Patlachique (2,700 m a.s.l.) are associated with forest conditions, where paleosols are characterized by polygenetic profiles with varying degrees of development. The older soils are represented by Luvisols. Soils in lower positions (Cerro Colorado, 2,390 m a.s.l.) are stratified and poorly developed, with evidence of colluvial deposition and erosion. Soils with fluvic properties in the alluvial plain (2,250–2,350 m a.s.l.) are also poorly developed and greatly influenced by erosive processes and intensive accumulation. Those corresponding to the Teotihuacan periods (2,000–1,350 yr BP) show multiple indicators of human impact. Micromorphological evidence indicates intensive agricultural activities (deforestation, burning, compaction, and erosion). The presence of carbonates in underlying strata is related to changes in humidity. Phytoliths identified from the same strata indicate alterations in vegetation through time that reflect variable conditions of temperature and humidity. The results clearly reflect environmental modification by human populations from the initial period of prehistoric settlement up to present. Furthermore, the evidence suggests that a major impact of the prehistoric city on the landscape resulted from unmanaged exploitation of forest resources that provoked intensive erosion and significant changes in the hydric conditions of the region.