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Summary Red palaeosols of the late Pleistocene-early Holocene, both buried and non-buried, were studied recently in Sonora (NW Mexico) to reconstruct their pedogenesis as well as the palaeoenvironmental conditions. The alluvial palaeosol-sedimentary sequence of the La Playa archaeological site is a key locality for the buried San Rafael palaeosol, which exhibits a 2Ah-2Bw-2BCk-3Bgk profile and was defined as a Chromic Cambisol. Radiocarbon dates from pedogenic carbonates and charcoal set the soil formation interval between >18000 and 4300calibrated years before present (cal. year BP). Micro-morphological observations together with profile distribution of clay, carbonates, organic carbon, pedogenic iron oxides and rock magnetic properties indicated a strong eluvial-illuvial redistribution of carbonates, moderate silicate weathering and gleying in the lower horizon. Although this soil was much more developed than the overlying syn-sedimentary late Holocene Fluvisols, clay mineral composition and stable carbon isotope signatures of humus and carbonates were similar in both soils. We suggest that pedogenesis of the San Rafael palaeosol took place under a slightly more humid climate and relative geomorphic stability. This agrees with the regional palaeoclimate reconstruction, which indicates a moister climate during the Late Wisconsin glaciation (MIS 2). An abrupt termination of the San Rafael pedogenesis marked by disturbance and aridization features in the Ap horizon of the palaeosol could be linked to a global drought around 4200years cal. year BP. Surface Chromic Cambisols in northern Sonora show similar pedogenetic characteristics to the buried red palaeosols of La Playa. They appear to be a relict component of the present day soil mantle.

Paleosol sequences along the lowest terraces of the Usumacinta River in southern Mexico were used to reconstruct Holocene environmental changes and examine human–environmental interactions. Study sections were correlated through paleosol morphology, radiocarbon dating, and artifact seriation of Formative, Classic, and Postclassic ceramics. The oldest paleosols have gleyic features. Although they contain hard carbonate concretions dating to 5450–5380 cal. yr B.P., these Gleysols formed in the Late Pleistocene to Early Holocene. Carbonates were deposited later. The uppermost paleosols lack gleyic features, the oldest of which contains vertic features, dating to 2000– 2700 cal. yr B.P., and contains abundant Formative period ceramics. The upper two paleosols are morphologically less developed and are strongly affected by human activities; radiocarbon ages and ceramic assemblages indicate that they belong to the Maya Classic and Postclassic periods. Stable carbon isotope values from the decalcified organic matter vary among paleosols of different ages and sites. δ 13 C values are highest (−16 to −20‰) in the Formative period paleosol. Although it is possible that maize cultivation could contribute to the isotopic signatures, we believe that the δ 13 C values indicate the dominance of drought-resistant C4 and CAM vegetation due to their association with vertic soils. The Classic period paleosol has a slightly lower isotopic value (−20 to −22‰), while the Postclassic paleosol shows the lowest values (−22 to −23‰), suggesting reforestation of the floodplain. These results indicate that the Early Holocene paleosols formed in a humid climate similar to that of today, which transitions toward dryer conditions around 5500 cal. yr B.P. In the Late Holocene (approximately 3000 B.P.) an increase in seasonality occurs. This condition favored the formation of Vertisols, suitable for agriculture. C � 2013 Wiley Periodicals, Inc.

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.

Cenotes (natural wells or sinkholes) comprise the most common landscape features in the northern Maya Lowlands of the Yucatan Peninsula, Mexico. Detailed study of dated soil-sedimentary sequences, recovered from a cenote at the archaeological site T’isil and nearby wetlands, allows a partial reconstruction of environmental variability at the site for the last 2000 years. Biogenic calcite sedimentation and Calcisol development occur during three intervals of increased inundation in cenote and wetland environments, ca. A.D. 300, A.D. 1000, and A.D. 1300. Periods of increased inundation in the cenote and wetlands correlate with wetter climatic intervals, and periods of Maya occupation at sites in the Yalahau region. Evidence for Maya modification of the cenote environment may relate to regional wetland agricultural practices.

Buried palaeosols of central Mexico, not previously analysed from a palaeopedological standpoint, have helped to develop a reliable regional model of Late Quaternary climatic change. This paper focuses upon morphological and micromorphological properties, particle-size distribution, and extractable Fe, Al and Si of seven palaeosols (named PT1–PT7) in the vicinity of the Nevado de Toluca volcano. The characteristics of Andic Cambisol PT1, similar to those of modern soils in semi-arid environments, indicate a drier climate in the first half of the Holocene. Humic Andosols PT2–PT4 are analogous to modern volcanic soils of humid forest environments. They show evidence that a moist palaeoclimate prevailed during marine oxygen isotope stages (OIS) 2 and 3. Luvisols PT5 and PT6, which are assumed to have formed at the end of marine OIS 5 to marine OIS 4, also indicate humid conditions. We attribute the differences between Andosols PT2–PT4 and Luvisols PT5–PT7 to variations in the duration in the pedogenesis rather than to changes in palaeoclimate. Micromorphological features of Andosol to Luvisol transition confirm that these soils form an evolutionary sequence. Being for the most part consistent with lacustrine records, the palaeosol properties do not reflect the episodes of ‘drier climate’ during the Last Glacial Maximum, however, as shown by diatom and palynological data from lake sediments. Mesoclimate variations and/or incompleteness of ‘soil memory’, reflecting mostly periods of humid pedogenesis, probably provide the reason for this disagreement. Copyright © 2001 John Wiley & Sons, Ltd.