engleski

The sedimentary record of Bansko brdo hill (NE Croatia): from Badenian marine environment to Pleistocene eolian sediments

Baranja region is located in the eastern part of Croatia. It is bounded from east and south, by the Dunav and Drava rivers and by Hungary from the north/north- west. Baranja is mostly covered by Pleistocene sediments, with some local outcrops of Miocene sediments. Pleistocene sediments are dominantly loess, loess- like sediments (marsh loess), fluvial, alluvial and marsh sediments, covering Baranja plains. Only high ground in Baranja is Bansko brdo hill (244 m), situated in the northern part of region, stretching in south-west to north-east direc - tion, about 20 km. Geological basement of Bansko brdo hill is made of sandstone limestone, marl, andesite, riolite and andesite breccias, which are of Miocene age. Due to faults, which are normal, outcrops of Miocene sedimentary and igneous rocks are present at the northern slopes of the hill. Southern slopes are covered completely with loess. Sedimentary rocks represent sea level fluctuations during Badenian and Sarmatian period in Central Europe and transition from sea water to brackish water. Fossils found in marls are typically marine. Igneous rocks are determined to be Badenian age and they are intruded into sedimentary rocks, during upper Badenian magmatic events in Panonian basin. During Pliocene and lower Pleistocene, last remnants of Paratethys disappeared. Plains in central Europe were covered by marshes and newly formed rivers. During middle and Upper Pleistocene climate in northern hemisphere was influenced by glacial/interglacial periods. During that time, loess was formed, mainly from moraine material, and transported by winds to the plains. Total estimated thickness of loess on Bansko brdo hill is about 30 m. Oldest loess sections at Bansko brdo, at Zmajevac profile is 121 ka, which is base of upper Pleistocene. This age represents last glacial period, which is called Würm, in Alpine division of Pleistocene. Paleosoils visible in 3 layers are present in loess. Loess is eolian silt. Bulk samples of loess were taken for mineralogical and paleontological analysis. Mineral composition of loess, from Bansko brdo hill reveals the origin of that eolian sediment. In light mineral fraction quartz and feldspar are dominant. In heavy mineral fraction amphibole, epidote and garnet are dominant. Complete mineral assemblage indicates that source material for loess was the Alps. Loess at Bansko brdo hill is rich in fossil mollusc fauna, land gastropods. Gastropod shells from 3 most abundant fossil species were analysed on stable isotopes ΔO18 and ΔC13 in IAMCCNR in Naples. Isotope results from loess sections, suggest a slight arid/humid and cold/warm variations in climate, during upper Pleistocene. These variations reflect stadial/interstadial climate changes in upper Pleistocene. Warmer and more humid periods, during last glacial are marked by 3 paleosoils which are inbeded in loess. Stable isotope data do not provide absolute numbers, just relative differences of Pleistocene and recent temperature/humidity. Due to that problem, shells of recent gastropods, collected from meadows, fields and loess sections were also analysed (ΔO18 and ΔC13). Numbers obtained from stable isotope results are matched with data of average annual temperature and humidity, at Bansko brdo for year 2009. (Beli Manastir meteorological station). These matched and calculated results, provide a certain standard, which can be used to determine (with caution) absolute temperature/humidity during upper Pleistocene. Results from recent gastropod shells and fossil gastropod shells, indicate significant difference in recent and Pleistocene climate (for Baranja region, which can be applied for southeast Europe). In general, in upper Pleistocene, climate was much more colder, than today, and also more arid. In some periods (interstadials) climate was more alike recent climate, but main trend was cold and arid climate, with average annual temperatures more than 7°C lower than today.

Baranja, Badenian, Pleistocene, marl, loess

nije evidentirano