A pedostratigraphic marker in the geomorphological evolution of the Campanian Apennines (Southern Italy): The Paleosol of Eboli

Abstract

The Paleosol of Eboli is interbedded within an Early Pleistocene coarse alluvial succession, the Eboli Conglomerates, located in the Campanian Apennines (Southern Italy), infilling the morphostructural depression of the Sele River Plain. Quaternary climatic changes and related morphodynamic response were investigated using a multidisciplinary (geomorphological, sedimentological and pedological) approach. The alluvial sequence of the Eboli Conglomerates shows remarkable vertical changes, marked by clear erosional discontinuities that identify four stacked formations called, from the bottom, Fontana del Fico, Colle Mancuso, Castelluccia, and S. Anna formations. The clastic facies of these formations are mainly indicative of an alluvial fan environment, with most sediments emplaced by flooding of distributary streams. The Paleosol of Eboli is formed at the top of the Castelluccia formation. We investigated its morphological, physical, chemical, micromorphological, and mineralogical properties. Many discontinuities appear in the field due to various erosional events that are related to hillslope dynamics. Each of these events was followed by the emplacement of new and different colluvial deposits that were derived from upslope and were subsequently affected by pedogenesis. All the horizons of the Paleosol of Eboli have reddish and brown matrix colours, secondary carbonate, angular blocky structure, and clayey texture. On the basis of the field data and chemical and physical analysis, three different pedogenetic cycles can be distinguished in the Paleosol of Eboli. These cycles depict differing degrees of pedogenic expression depending on water regime and duration of pedogenesis. The micromorphology showed the presence of eluvial tongues, Fe dynamics (coatings, segregations), vertic features (optically anisotropic lines in the soil matrix), and pedorelicts. Kaolinite is the most abundant clay mineral, but vermiculite and illite are also present. The Fe minerals, especially the hematite/goethite ratio, have provided a new approach to understand the main paleoclimatic changes through the studied sequence. The overall pedogenetic scenario depicts a highly weathered environment (disordered kaolinite, Fe oxides, low Feo/Fed ratio, depletion zones), characterized by marked climatic seasonality (witnessed by vertic properties) and abundant rainfall (depletion zones). The general scenario is coherent with a highly weathered subtropical environment that probably occurred during MIS-25, based on age control. The widespread outcrop pattern, consistent stratigraphic position, thickness ranging from 1 to 5 m, and the uniformity of pedological features of the Paleosol of Eboli make it clearly recognizable in the field and allow us to consider the Paleosol of Eboli a reliable pedostratigraphic marker.