The loess-paleosol sequence at Monte Netto: a record of climate change in the Upper Pleistocene of the central Po Plain, northern Italy

Purpose At the northern fringe of the Po Plain (northern Italy), several isolated hills exist, corresponding to the top of Late Quaternary anticlines. These hills were thoroughly surveyed for their soils and surficial geology, furnishing detailed archives of the palaeoenvironmental evolution of the area. A new, thick and complex loess-paleosol sequence, resting upon fluvial/fluvioglacial deposits, exposed in a quarry at the top of the Monte Netto hill was studied in detail to elucidate its significance. Materials and methods Highly deformed fluvial and fluvioglacial deposits, probably of Middle Pleistocene age, are exposed in a clay pit at Monte Netto, underneath a 2- to 4-m-thick loess-paleosol sequence. A geopedological, sedimentological and micropedological investigation of the sequence shows a distinctive difference between the B horizons forming the sequence, while luminescence and radiocarbon age determinations and the occurrence of Palaeolithic lithic assemblages elucidate the chronology of the sequence. Results and discussion The pedosedimentary sequence consists of several loess layers showing different degrees of alteration; loess deposition and weathering occurred, according to optically stimulated luminescence (OSL) and AMS-14C dating as well as archaeological materials, during the Upper Pleistocene. The lower part of the section consists of strongly weathered colluvial sediments overlying fluvial and fluvioglacial sediments. A tentative model of the exposed profiles involves the burial of the anticline, which forms the core of the hill, by loess strata since Marine Isotopic Stage (MIS) 4 and their subsequent weathering (and truncation) during subsequent interstadials. The degree of weathering of buried B horizons increases from the top of the sequence toward the bottom, suggesting a progressive decrease in the intensity of pedogenesis. Finally, the highly rubified paleosol at the top of the hill is regarded as a buried polygenetic soil or a vetusol, developed near the surface since the Middle Pleistocene. Conclusions The palaeopedological, geochronological and geoarchaeological analyses permit to define the phases and steps of development of the Monte Netto pedosedimentary sequence; the lower part of the sequence is dated to the Mid-Pleistocene, whereas loess accumulation occurred between MIS 4 and MIS 2. Moreover, analyses help to clarify the climatic and environmental context of alternating glacial and interstadial phases, during which the sediments where deposited, deformed and weathered.