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Mineralogical, geochemical and micromorphological characteristics of red palaeosol situated on the limestone at the base of the Pleistocene loess-palaeosol sequence in Savudrija, Istria

A 7.5 meter thick loess-palaeosol sequence (LPS) was investigated in Savudrija, Istria. Within LPS, 18 horizons (recent soil, palaeosols and loess) were recognized. During the field investigation, the morphological properties of each horizon were described in detail and samples were taken along the LPS. Here we present the results of the investigation of the red palaeosol covering the carbonate basement exposed at the bottom of the investigated LPS (horizons 17 and 18) and its immediate cover (horizons 15 and 16). Our aim was to determine the provenance of the palaeosol parent material and to reconstruct the palaeopedological processes that occurred during its formation. Laboratory work consisted of a detailed chemical analysis, analysis of iron and manganese oxides and hydroxides soluble in oxalate and dithionite, physical and chemical analysis of the palaeosol, particle size analysis, mineral composition analysis using the X-ray diffraction method, optical and infrared stimulated luminescence and lastly, a micromorphological analysis of thin sections. The immediate cover of red palaeosol is pedogenically altered loess (horizons 15 and 16). From top down, the investigated section comprised the following mineral horizons: Ck2– BC – Bg2 – Bg – R (WRB, 2006). The study showed that the red palaeosol formed in a lithologically uniform material that dominantly presents a mixture of loess and, partly, remains of older soils that existed on the surface of the Cretaceous limestone. This is proved by the presence of pedorelicts found in the red palaeosol which represent fragments of these older soils. The clay fraction of all analysed samples contains illitic material, well and poorly crystallized kaolinite, goethite, haematite, 14 Ǻ minerals and mixed layer clay minerals. Therefore, we can conclude that the main processes that governed the formation of red palaeosol were decalcification, rubification and bisialitization. Mineral composition, content of dithionite soluble iron and the lack of clay coatings clearly indicate that the red palaeosol situated at the bottom of Savudrija pedosedimentary complex is different from the majority of terra rossa soils in Istria. Concretions and dispersions of calcite that were observed within the red palaeosol represent secondary carbonates which (re)precipitated only after they were leached from the overlying loess, which buried the non- calcareous “Terra-Rossa-like” soil. According to ZHANG et al. (in preparation), the age of the investigated section correlates with the OIS 4 stage.

loess-palaeosol sequence, red palaeosol, clay mineralogy, micromorphology, luminescence dating, Savudrija, Istria

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