engleski

Relation of lithified terra rossa-like infillings in limestone cracks and cavities to red paleosols on limestone at the base of the loess sequence on Susak: a high-resolution depth and chronological approach

Cracks and cavities in Senonian limestones on the island of Susak are often filled by lithified terra rossa-like materials. We consider them residues of the oldest paleosol(s) on the island. The same surface is covered by up to 90 m of loess intercalated with many paleosols and at least three tephra layers. The lowermost red paleosol up to 100 cm thick covers the carbonate bedrock. Within this paleosol, E, EBt and Bt horizons were recognized. The clay mineral fraction of this paleosol contains illitic material, 14 Å clay minerals, kaolinite and mixed layer clay minerals. From the mineralogical and geochemical view point two different types of lithified terra rossa are situated within cracks and cavities of limestone. Compared to the first one which after removing secondary carbonates contains kaolinite, mixed-layer clay minerals and illitic material as main mineral phases (lithified terra rossa 1), the second one is after removing secondary carbonates enriched in gibbsite, boehmite, kaolinite and haematite (lithified terra rossa 2). The three red paleosols also show distinctive Fed/Fet and Feo/Fed values and specific Al/Si, La/Ce and U/Th, molecular ratios which we use as weathering and/or provenance indicators. The first dating study of the loess – palaeosol sequence on Susak was performed by WACHA et al. (2011 a, b) and showed that most of the exposed sedimentary record can be correlated with oxygen isotope stages (OIS) 5 to 2. A more detailed dating study is in progress. With the means of IRSL dating methods and high-resolution palaeomagnetic measurements we will try to provide age(s) of the lowermost red paleosol that covers the carbonate bedrock and acquire new information about lithified red paleosol(s) in limestone cracks and cavities. The first IRSL measuring tests show dose saturation which could indicate a very old age of the red paleosol that covers the carbonate bedrock (beyond the limits of the method) but more measurements are needed and are in progress. Also, the first palaeomagnetic data for lithified terra rossa containing gibbsite and boehmite are far away from the present (Quaternary) magnetic field which is recorded in the loess/paleosol sequence.

terra rossa; limestone; cracks; paleosols; Susak; high-resolution

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