Prapor je sediment nastao taloženjem čestica silta eolskim transportom. Zbog svojih karakteristika predstavlja kvalitetan zapis klimatskih promjena u kasnom pleistocenu. Najdeblji profili prapora u Republici Hrvatskoj nalaze se u regiji Baranja. Odabrana su četiri izdanka koji čine dva profila prapora. Analizom sedimentoloških karakteristika prapora i odredbom specifičnih zajednica malakofaune utvrditi će se izvorišno područje prapora, način transporta zrna silta te intenzitet utjecaja paleoklimatskih promjena na malakofaunu. Napravljene su granulometrijska, kalcimetrijska, modalna, magnetometrijska analiza i snimljene su fotografije zrna kvarca elektronskim mikroskopom. Određene su specifične zajednice malakofaune, a analizom stabilnih izotopa kisika i ugljika na kućicama malakofaune kvantificirani su podaci o paleoklimatskim promjenama. Modalne analize pokazuju da je izvorišno područje za naslage prapora u Baranji prostor Alpa te manjim dijelom i zapadnih Karpata. Teksture vidljive na površinama zrna ukazuju na različite načine transporta kvarcnih zrna, a uključuju glacijalni transport, transport vodenim tokovima i eolski transport. Eolski transport je proksimalnog karaktera. Prapor Banskog brda može se podijeliti na tipični prapor, padinski prapor i lesoliki sediment. U oba profila prapora utvrđeno je pet hladnodobnih, karakterističnih malakofauna. Prevladavaju termofilne i mezofilne vrste s manjim udjelom kriofilnih vrsta. Dominira Helicopsis striata fauna. Stabilni izotopi kisika pokazuju da je prosječna temperatura ljetnih mjeseci na području Baranje varirala 14,44 ºC u periodu kasnog pleistocena i da je klima bila znatno hladnija nego danas. Vrijednosti stabilnih izotopa ugljika određuju vrstu prehrane malakofaune i posredno ukazuju na pretežno vlažnu klimu.
|Abstract (english)|| |
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 palaeosol horizons forming loess-palaeosol successions. Due to its characteristics loess represents a high quality record of climate changes in the Late Pleistocene. The thickest and best-studied loess sections in the Republic of Croatia are located in the eastern Croatian province of Baranja, near the Danube River. The main scope of the thesis was to determine the sedimentological characteristics and source area of the studied loess, to establish specific malacofaunal assemblages and to reconstruct regional paleoclimate changes during the Late Pleistocene. A combination of sedimentological analysis of loess, along with palaeontological and stable isotope analysis of malacofauna provide results regarding depositional cycles and the impact of climate change on loess formation and the malacofauna contained within it.
Results of the sedimentological and mineralogical analysis provide information on the source area of silty material, as well as the input direction of silt particles. The result of palaeontological analysis of malacofauna define palaeoclimate and palaeoenvironmental changes in the Late Pleistocene. Four loess outcrops at Bansko brdo hill in Baranja were chosen for study. They form two profiles: northern and southern. A total of 30 bulk samples (8-10 kg of loess) was analysed using several approaches: grain-size analysis, modal analysis, carbonate content analysis, scanning electron microscopy, palaeontological analysis and measurements of oxygen and carbon stable isotopes. Additionaly, a series of 47 samples from loess and palaeosols was collected to obtain information regarding vertical changes in magnetic susceptibility which provides data about magnetic mineral content in the loess and palaeosols.
Median grain-size of loess samples is 0,033 mm in the northern profile and 0,031 mm in the southern profile. Carbonate content in loess ranges between 2,9% and 23,3%. Modal analysis pointed out the light mineral fraction as being dominant in all samples with the heavy mineral fraction ranging from 4,15% to 11.21%. Quartz is the dominant mineral in the light mineral fraction ranging between 50% to 74% (mean value 59.5%). The most common transparent heavy minerals are the mineral groups of epidote, garnet and amphibole; all three range from 25 to 30%. Images of quartz grains acquired with scanning electron microscope display a variety of textures which are the product of mechanical weathering during transport. Transport of silt and sand grains was complex and included glacial, fluvial and aeolian phases. Magnetic susceptibility (MS) values from the loess range from 5x10-6 SI to 28.5x10-6 SI. The average value in palaeosols in the southern profile is 65,25x10-6 SI. Palaeosols from the northern profile display significantly lower average values of 33,7x10-6 SI. Terrestrial gastropod palaeoecology based on 5971 specimens of 21 species counted from the loess, documents cyclic transitions between cryophilous to cold resistant and mesophilous to thermophilous assemblage types. Species tolerating open and dry habitats are abundant in both profiles. Five specific faunas which are all cold resistant were determined in the loess samples. Helicopsis striata fauna is the most dominant among five faunas in both profiles. Stable oxygen values range from -5,89 to -2,15. Stable carbon isotope values range from -10,00 to -6,45.
Grain-size distribution indicates that the loess from Bansko brdo hill in Baranja is typical loess, comparable with other loess profiles in the Pannonian Basin. Slope loess and loess-like sediment were also determined in Baranja. Garnet, epidote and amphibole mineral group are most abundant heavy minerals in sediment samples of modern Danube, Drava and Tisza Rivers. By comparing this data with the heavy mineral assemblage for the Baranja loess, it is obvious that main source area for the loess is from the Danube, Drava and Tisza flood plain sediments. The source areas for those river sediments were the Alps and Western Carpathians. The main aeolian transport direction was from the North or North-West. Textures and shape of quartz grains observed with scanning electron microscope indicate a complex transport composed of several phases, from initial glacier transport to fluvial transport and temporary floodplain storage to final, proximal aeolian transport phase. The faunal assemblages in the loess samples prove the dominance of transitional palaeoecological assemblage types, whereas uniformly defined types are rare. Stable oxygen values show significant palaeotemperature changes during the Late Pleistocene with average summer temperature changes in range of 14,44 ºC. The overall climate was much cooler then present. Stable carbon isotope values point to humid conditions in the Late Pleistocene. Magnetic susceptibility data indicates high amounts of magnetic minerals in palaeosols, which points to warm and humid climate during formation. Palaeosols were formed in warmer and more humid climate conditions of the Late Pleistocene during interglacial and interstadial periods. Loess was deposited in colder and more arid climate conditions during glacial and stadial periods in Late Pleistocene.