Soil development on marine terraces near Metaponto (Gulf of Taranto, southern Italy)

Abstract

For decades, the marine terraces in the Metaponto area have been the subject of discussions concerning their number, sedimentology, genesis and age. This paper contributes to landscape history reconstruction from a pedogenetic view. The marine terraces are generally covered by loamy sediments, which have been interpreted in previous works as lagoonal and/or alluvial sediments, deposited shortly after the emergence of the land surface above sea level. Pedogenetic investigation, including field observations (e.g. soil colour, intensity of weathering, precipitation of secondary carbonates) and Fe d/Fe t ratio, silt/clay ratio and carbonate content, reveals that the usual sedimentation history on the terraces includes a period of soil formation between the deposition of the marine and that of the alluvial sediments. Most likely, soil formation began after the relative sea level maximum within the same interglacial during which the marine terrace formed. Later, alluvial sediments accumulated during a time of periodic flooding, while soil development in the underlying marine sediments probably continued at reduced rates. One central question of this study is whether soil formation indicates progressive ages of the terraces. The complex landscape history involving several sedimentation and erosion phases makes the correlation of soil development stages with terrace ages difficult. Nevertheless, maximum Fe d/Fe t ratios and (Ca + Mg + K + Na)/Al ratios of the soils developed in the different sediments plotted vs. assumed terrace age indicate increasing soil development. The relationship between Fe d/Fe t ratios and terrace age can be best described by power ( R 2 = 0.89) or logarithmic functions ( R 2 = 0.72), both describing a strong increase in pedogenic iron in the first 100 ka which slows down afterwards. (Ca + Mg + K + Na)/Al ratios follow a logarithmic decrease with time ( R 2 = 0.99), indicating progressive silicate weathering, associated with element release and leaching.