engleski

The Last Glacial loess-palaeosol sequence at Savudrija (Istria, Croatia), its origin, age and palaeosol properties

The loess-palaeosol sequence at Savudrija (Istrian Peninsula, Croatia) is ~ 7.5 m thick and superimposed on the top of the Cretaceous limestone. It consists of loess and sandy loess intercalated with four brown palaeosols, and one red palaeosol at the bottom of the sequence. High-resolution sampling was applied with the purpose to reconstruct the genesis and origin of the deposits, as well as to reconstruct the climate conditions that influenced the formation of such deposits in the area. To establish its chronological framework, OSL and IRSL dating, accompanied by palaeomagnetic analyses, were applied. Palaeosol and sediment layers within the section were identified, described and labelled. Basic chemical and physical properties of each identified layer were analyzed. Heavy and light mineral analysis was performed, to determine the provenance of the parent material. Mineralogical, geochemical and micromorphological analysis of the uppermost loess and the red palaeosol at the bottom of the section were performed to reconstruct the palaeopedological, palaeoenvironmental and palaeoclimatic conditions which influenced their formation. Palaeo- and rock-magnetic measurements were performed to support the dating results and to characterize the magnetomineralogy of the sediments. The obtained luminescence ages and palaeomagnetic data demonstrate that the Savudrija loess-palaeosol sequence was formed between ~70 ka and ~9 ka (Zhang et al., in press), which correlates well to the time span from the last glacial to early Holocene. The variation of the magnetic susceptibility of the Savudrija section is following the pattern in which the palaeosol horizons generate high susceptibility values while the loess horizons show low susceptibility values. Both the bulk mineralogy and heavy and light mineral fraction show that the red palaeosol situated on the Cretaceous limestone has a similar provenance as the uppermost loess. However, both the type and share of clay minerals in the clay fraction of loess and the red palaeosol differs. The main clay mineral phases in the clay fraction of loess are 14Å minerals (vermiculite and/or smectite) and illitic material, while mixed- layer clay minerals, kaolinites and chlorite are subordinate. The composition of the red palaeosol indicates moderate weathering of the parent loess material. Main mineral phases are mixed-layer clay minerals and kaolinites (both well and poorly crystallized), while illitic material is subordinate. Secondary carbonates observed in the red palaeosol (re)precipitated only after they were leached from the overlying loess, which buried the noncalcareous “Terra- Rossa-like” soil. A few rounded clay coatings non-related to macrovoids found in the red palaeosol probably represent the transported remains of older soils that existed on the surface of the Cretaceous limestone. We can tentatively conclude that the red palaeosol at the bottom of the section 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. Furthermore, the magnetic susceptibility record suggests that the age of ~70 ka of the red soil at the bottom of the section might be still ambiguous and needs further study.

loess-palaeosol sequence, luminescence dating, MS, high resolution grain size analysis, Istria Croatia, Adriatic loess region

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