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IRSL Dating of a Quaternary Sediment Succession in Šarengrad, Eastern Croatia

1. Introduction A 23 m thick succession of Quaternary deposits has been documented and described at Šarengrad, a village situated on the right bank of the river Danube in Eastern Croatia (Fig. 1a). In the easternmost part of Croatia, from Vukovar to Ilok, loess and loess-like deposits up to 30 m thick predominate, forming a loess plateau. During the fieldwork in April 2008, 52 samples for malacological investigations and 3 samples for infrared stimulated luminescence (IRSL) dating were collected in Šarengrad. The preliminary results of the malacological investigations have been published by HUPUCZI et al. (2010) correlating the investigated sequence to the Last Glacial - Interglacial cycle. This paper presents the result of the infrared stimulated luminescence (IRSL) dating from the three samples. This work is a result of the bilateral Croatian-Hungarian project financed by the intergovernmental TÉT foundation (CRO-16/2008) and the Croatian Ministry of Science, Education and Sports (Project Nr. 181-1811096-1181) 2. Lithology of the section The base of the investigated Šarengrad section consists of about a metre thick yellow to light-brown micaceous, fine-grained sand and sandstone of fluvial origin (Fig. 1b and c). The sand fines upwards into a 3 m thick greyish sandy-silty clay and clay with red tint due to dispersed limonite (Fig. 1c). This clay is overlain by greyish variegated clay with red and brown stripes and patches caused by enrichment in dispersed limonite and manganese accumulations. The lower part of this horizon is intercalated by a thin layer of carbonate accumulations. The clays represent marshy sediments and are overlain by greyish-yellow clayey silt containing calcareous nodules, a transitional layer between swamp deposits and loess, the so called infusion loess. The transition between these two units is gradual. The homogenous unstratified slightly micaceous yellow silt with numerous gastropod remains covers the marshy sediments and represents the oldest loess, which is the parent material of the overlying 2 m thick paleosol. The paleosol consists of a transitional horizon on the top, an “AB” horizon in the middle and a thin “C” horizon at the bottom. The “AB” horizon is made of red-brown silty clay and is, getting darker with depth. The fossil soil level is strongly compacted, homogenous and unstratified. Under the “AB” horizon a 0.2 m thick horizon of carbonate accumulation and cementation can be recorded. Based on the nearby Quaternary sequences of the Ilok sandpit and the Ilok brickyard this paleosol can be categorized as a chernozem-brown forest type fossil soil horizon. This fossil soil is covered by an about 7 m thick loess horizon. The loess is well-sorted, homogenous, unstratified, and pale-yellow to greyish-yellow containing tiny, dark brown manganese dots and white calcareous veins and flakes. It consists of slightly- or medium-micaceous silt. The calcareous nodules are dispersed in the complete loess layer, occasionally forming layer-like intercalations. The nodules range in size from 1 to 10 cm. The malacological samples were collected only from the lower 3 m of this loess horizon (Fig. 1c). Above this thick loess horizon is a double fossil soil, build up of two paleosol subhorizons. It is overlain by a loess layer seen at the uppermost, unreachable part of the section. 3. IRSL dating Three samples for IRSL dating were collected from the investigated section, one from the oldest loess about 60 cm below the lower paleosol and two from the loess covering the lower paleosol (Fig. 1c). For the measurement of the feldspar IRSL signal the elevated temperature post-IR protocol presented by BUYLAERT et al (2009) was used. This protocol proved to be successful for dating of loess deposits beyond ~ 100 ka and has the advantage of minimizing the anomalous fading (THIEL et al., submitted), an unwanted effect which causes age underestimation. 4. Conclusion The preliminary results showed that the elevated temperature post-IR protocol has potential for dating of loess deposits older than ~ 100 ka, an age range which lacks appropriate dating methods. Dating results of the samples from Šarengrad indicate ages much older than the Last Glacial/Interglacial, suggesting a Middle Pleistocene loess-paleosol record in Šarengrad. Based on the IRSL dating results from the lower most sample which gave an age of about 344 ka the lower paleosol can be correlated to oxygen isotope stage (OIS) 9 and the double paleosol to OIS 7. Similar Antepenultimate Interglacial double paleosols have commonly been described in European loess stratigraphy. The section under study shows an excellent transition from sediments deposited in a waterlain marshy environment to sediments deposited under subaerial environment. The deposition of the loess started at least prior to 350 ka before present. A similar sediment succession can also be seen in the Ilok sandpit. These results present the first dating attempt of older loess-paleosol sequences in Croatia.

Eastern Croatia; Lithostratigraphy; Marshy sediments; Loess section; IRSL dating; Middle Pleistocene

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