Macro/micromorphological features and some other climatic proxies in paleosols and polygenetic soils

Basic concepts of Lyell’s geological principle of actualism, even earlier applied in the first half of the 18th century, represent valid basis for the use of paleosols and polygenetic soils as indicators of past climatic conditions and changes. Observations acquired progressively more potential of understanding, as far as discovery and implement of new analytical techniques permitted integration of field-scale soil description with investigations at microscopic and submicroscopic levels, as well as quantification of morphological, chemical and mineralogical properties. Many papers focus on interpretation of macro- and micromorphological soil features in terms of nowadays inactive (relict) pedogenetic processes under different climates and reconstruction of associated paleoenvironments. Weathering degree and thickness of saprolites are also used as paleoclimatic indicators, along with peculiar deposits alternated with paleosols (alluvial and marine sediments, periglacial debris slope deposits and loess). Layered soils often permit to emphasize pedogenetic and geomorphic responses to different-order climatic cycles and give some constraints to their time recurrence. Special interest is devoted to identification of features diagnostic of interglacial and glacial periods. Clay coatings and rubification are investigated in detail as typical features of interglacials, and platy structures, silt coatings/cappings, degenerated clay pedofeatures, vesicular pores, etc. often interpreted as cryogenic features developed during glacials. Some geochemical indices are valuable tools for quantitative estimation of soil processes (leaching, base loss, oxidation) and paleo-precipitation. Further quantification of paleoclimatic variations can be achieved using stable isotopes, delta13C in humic soil horizons and delta18O in pedogenic carbonates. Identification and quantification of pollens, charcoals and phytoliths in soils can also supply information on past vegetation and its dynamics.