Adding information about soils and paleosols to geological maps, through the application of the “pedostratigraphic level” concept

Abstract

Paleosols are rarely reported on geological maps. However, their mapping and study can add a great deal of information, useful to the understanding of Quaternary geological and geomorphological processes. This study was aimed at developing a methodology that uses soil surveys and paleopedological studies to create a detailed map of Quaternary cover, suitable for integration with a standard geological map of similar scale. This study was conducted in the Montagnola Senese area of central Italy. Landscapes there included a small ridge made up of carbonate free metamorphic rocks, and calcareous deposits. Quaternary paleosols formed on slope and alluvial deposits derived from this bedrock were particularly abundant. The map of Quaternary cover was developed from the pedostratigraphic map, as a function of thickness of the regolith and age of the oldest pedostratigraphic level. A pedostratigraphic level was defined as a characteristic assemblage of soil genetic horizons, formed in materials having a certain degree of weathering and the age that was estimated by means of correlation to benchmark soils. Pedostratigraphic levels were generated from a Soil Information System, where digital soil maps and soil attributes were stored. Soil attributes derived from routine surveys, as well as from specific investigations and analyses performed in order to determine the pedogenetic processes active in the Montagnola Senese during the Pleistocene. The information coming from the map of Quaternary cover was used to generate a new geological map of the area, where Quaternary deposits were divided according to their estimated age (early, middle and late Pleistocene, and Holocene), thickness, and morphological position.