The last interglacial pedocomplexes in the litho- and morpho-stratigraphical framework of the central-northern Apennines (Central Italy)

Abstract

Recently in Italy, a great deal of effort has been devoted to the mapping of Quaternary continental deposits. Several Unconformity Bounded Stratigraphic Units (UBSU) have been defined. The unconformities indicate important phases of changing dynamics linked to Quaternary climatic changes, and have been related to valley downcutting simultaneous with paleosol formation during interglacials. However, glacial periods are characterised by deposition of thick continental sequences. We suggest that the UBSU's belonging to the late Middle Pleistocene (MIS 6) and Late Pleistocene can also be defined under a pedostratigraphic point of view. Locally at the top of the UBSU attributed to MIS 6, buried or relict paleosols are preserved. The paleosols developed in calcareous fluvial and moraine gravels with minor flints. The pedocomplexes are made of three paleosols separated by erosion surfaces and/or stonelines. The older paleosol (MIS 5e) is severely truncated and is characterised by a Ck horizon overlain by strongly leached reddish Bt horizons with flinty rock fragments (with a diagnostic wavy lower boundary). In some sites, subsequent secondary precipitation of carbonates transformed this horizon into a Btk. This paleosol is buried by a younger paleosol (MIS 5c) with less leached reddish Btk horizons, quartz of aeolian origin, and very small and scarce calcareous clasts. The main pedofeatures are associated with colluvial processes, biological activity, and carbonate precipitation. This paleosol is also truncated and buried under a similar paleosol (MIS 5a). Therefore, the lower paleosol of the pedocomplex can be attributed to the Eemian, and constitutes a valid marker for the definition and mapping of the underlying and overlying sedimentary units. In other parts of the Apennines, no sedimentary units have been found that correspond to the unconformities separating different pedostratigraphical units. In order to map the different UBSU's, due to the poor lateral continuity of the preserved paleosols, morpho- and litho-stratigraphical investigations and correlation are always recommended.