Pedostratigraphy of Terra Rossa and Quaternary geological evolution of a lacustrine limestone plateau in central Italy

Pedostratigraphic levels (PLs) are typical assemblages of soil-genetic horizons, formed by materials having the same degree of weathering. The pedostratigraphic approach can be very useful to comprehend the formation of the Quaternary soil cover, the environmental evolution of a territory, and to estimate the age of paleosols. A pedostratigraphic study of a Terra Rossa was carried out to understand the soil–parent material origin and to estimate the time of the beginning of pedogenesis. Besides soil and geomorphological survey, the Terra Rossa was analyzed for Fe forms, geochemistry, clay mineralogy, micromorphology, and with scanning electron microscope. Optical dating was applied to obtain age estimates for the deposition of the parent material of soil formation. The insoluble residue of limestone was obtained and analyzed for geochemistry and clay mineralogy. The bedrock is constituted by Quaternary lacustrine limestone, showing pronounced karst landforms. The soil profile is situated in a little dissolution doline and was divided into three PLs: PL1 (0–110 cm) is constituted by cambic and ochric horizons, formed during Holocene in a mixture of colluvial soil sediments and fresh limestone, with aeolian components; PL2 (110–290 cm) includes two argic horizons, which began to form during Late-Middle Pleistocene in colluvial soil sediments, with few aeolian additions; PL3 (290–330cm) is constituted by a red argic horizon, with nitic properties, which developed from the insoluble residue of the limestone. The age of PL3 was calculated through a mass balance and an estimation of the limestone-dissolution rate during the Quaternary, which led to an approximate age of Middle Pleistocene, between 250 and 500 ky BP. The time of the beginning of pedogenesis on limestone can be used as a reference for the tectonic uplifting of the area and emersion of the plateau.