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Sedimentary characteristics and source of loess in Baranja (eastern Croatia)

Loess is terrestrial clastic sediment, composed dominantly of silt-sized particles formed by the accumulation of wind-blown dust. It is usually inter-bedded with soil horizons forming loess-paleosol successions (LPS). Zmajevac loess-paleosol sequence (LPS) of the northeastern Baranja is exposed along the southern slope of Bansko Hill on the western bank of the Danube River. The investigated 17.5m thick section shows 4 paleosols embedded in loess. 13 bulk samples were collected in loess of the Zmajevac LPS. Grain-size, modal and CaCO3 analyses were done on all samples together with. Series of 44 samples were collected to get information about vertical changes of magnetic mineral content in Zmajevac LPS. Each sample was measured 3X for avoiding deviation in results. Grain-size analysis proved silt as dominant grain-size fraction in all 13 samples. Median grain-size is constant between 0.025-0.03 mm. Skewness is fairly constant in samples, with average value of 0.78. Sorting is dominantly poor with average value around 1.5. CaCO3 content ranges in samples between 2.9% and 23.3%. Modal analysis pointed out the light mineral fraction (LMF) as dominant in all samples with the heavy mineral fraction (HMF) ranging from 4, 15% to 11.21%. Quartz is dominant mineral in LMF ranging between 50% to 74% (mean 59.5%). In HMF the transparent heavy minerals (THM) are more common than opaque ones. The most common THM are the mineral groups of epidote, garnet and amphibole. Epidote group is most abundant and ranges from 17% to 37% (mean 27.5%). Magnetic susceptibility (MS) values from loess range from 5 to 28.5x10-6 SI. The uppermost paleosol horizon (F2) shows highest measured values within the section (82.5x10-6 SI). The pedocomplex constituents F3a (67.7x10-6 SI ) and F3b (53.2x10-6 SI ) are marked by significant peaks that are however lower than in the F2 horizon. The lowermost paleosol F4 shows MS values of 58.3x10-6 SI. The results of grain-size and modal analysis provide information about source material and wind direction in different time periods during Pleistocene. Grain-size distribution is in good accordance with other loess localities in the Pannonian Basin. Garnet, epidote and amphibole mineral group are most abundant heavy minerals in samples of Danube River sediment. Comparing heavy mineral assemblage from Zmajevac LPS with that data, it is obvious that main source area for loess in Baranja is from Danube flood plain sediments. Main transport direction was from North or North-West. Nevertheless the higher concentration of amphiboles in Zmajevac LPS (mean 28, 8% in HMF) then in the Danube plain suggests additional source area. Western Carpathians with Neogene calc-alkaline volcanic rocks is major source for amphiboles. Alternatively those minerals could be from locally exposed volcanic and metamorphic rocks of the southward Slavonian Mts. Mt. Krndija and Mt. Papuk, which are closest to Baranja of all Slavonian Mts., consist of amphibolites. Results obtained from sedimentological and MS analyses show fairly good congruence with results from other LPS in the Pannonian basin, with some differences in mineral composition which imply diversity of source area for Baranja loess.

loess; Baranja; pleistocene; quartz; heavy mineral fraction

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