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The Pliocene Paludina Lake of Pannonian Basin : new evidence from northern Serbia

Rundić L., Vasić N., Životić D., Bechtel A., Knežević S., Cvetkov V.

Annales Societatis Geologorum Poloniae

2016

Vol. 86, No. 2

185--209

This study from the Sremski Karlovci clay pit in northern Serbia sheds new light on the physicochemical conditions, ecology and evolution of the Paludina Lake – the Pliocene successor of the late Miocene giant Lake Pannon hosted by the Pannonian Basin. The multidisciplinary study combines sedimentology, sequence stratigraphy, biostratigraphy, palaeontology, palaeobotany, coal petrology, organic geochemistry and magnetic mineralogy. The sedimentary succession studied represents the lake margin at the foot of the Fruška Gora ridge. Sedimentary facies reveal minor and major lake-level changes, including a forced regression with fluvial valley incision in the succession middle part and the ultimate emergence and covering of the lake floor by Pleistocene loess. Mollusc and ostracod fauna indicates an oligohaline shallow cool-water environment, no deeper than 5–6 m, with an active inflow of spring water. The lake local depth during transgression maxima did not exceed 20 m. Palynological and geochemical analyses indicate a rich and diversified assemblage of gymnosperm plants with a contribution of angiosperms, weeds and microbial biomass in the peat-forming suboxic to oxic coastal swamp environment. Maceral analysis of organic matter shows a prevalence of huminite, accompanied richly by inertinite in lignite and by liptinite in clay. The Pleistocene shift to terrestrial semiarid environment resulted in oxidizing groundwater conditions, with the reddening of sediments around a fluctuating groundwater table and the diagenetic transformation of bacteria-derived greigite into magnetite. In regional stratigraphy, the occurrence of Viviparus neumayri Brusina in the lower half of the succession indicates the Lower Paludina Beds of Dacian Stage (early Zanclean age). Other gastropods and certain ostracodes indicate transition to the Middle Paludina Beds of lower Romanian Stage (late Zanclean–early Piacenzian). The upper half of the succession lacks age-diagnostic fossils and is considered to represent Middle Paludina Beds with a possible relic of Upper Paludina Beds at the top.

Organic geochemical study of the Lower Miocene Kremna Basin, Serbia

Perunović T., Stojanović K., Simić V., Kašanin-Grubin M., Šajnović A., Erić V., Schwarzbauer J., Vasić N., Jovančićević B., Brčeski I.

Annales Societatis Geologorum Poloniae

2014

Vol. 84, No. 3

185--212

The Kremna Basin is located in southwest Serbia, in the Zlatibor area, which is part of the Internal Dinarides. This basin is noteworthy because of the type of bedrock drainage, which it represents. It was formed on ultrabasic rocks and volcanic materials that influenced the occurrence of organic matter (OM) in the basin fill. The objective of the study was to determine the organic geochemical characteristics of sediments from the central part of the Kremna Basin. The sediments studied belong to an intrabasinal facies, in which two sequences were distinguished. The lower sequence occurs at depths of 216–343 m, while the upper sequence is found from 13.5–216 m. At the start of basin development (265–343 m) sedimentation took place in shallow alkaline water, rich in Mg ions. Through time, a slight deepening of the basin occurred. This was followed by chemical deposition of carbonates (216–265 m). The most important change in the sedimentary environment occurred with the formation of sediments marking the transition between the sequences (at about 200 m). Sediments from the lower sequence are characterized by the dominance of dolomite and magnesite. There are indications of volcanic activity, i.e. tuff layers and the presence of searlesite. The upper sequence is characterized by the prevalence of calcite and dolomite. The amounts of MgO, Na2O and B are higher in the lower sequence, whereas the CaO content is higher in the upper sequence. The sediments contain different amounts of immature OM (late diagenesis). Biomarker analysis shows diverse precursors of the sedimentary OM: methanogenic archaea, photosynthetic green sulfur bacteria (Chlorobiaceae), bacterivorous ciliates, various bacteria, both photosynthetic and non-photosynthetic, the green unicellular microalga, Botryococcus braunii race A (exclusively in the upper sequence) and terrestrial plants. The lower sequence contains lower amount OM, composed primarily of kerogen II/III and III types, indicating a higher contribution of the allochtonous biomass of land plants from the lake catchment, particularly in the lower part. The sediments of the upper sequence are enriched in autochthonous aquatic OM, which comprises mostly kerogen I, I/II and II types. The transition from the lower sequence to the upper one is associated with a decrease in pristane to phytane ratio, gammacerane index and content of C28 steroids, absence or significantly lower amount of squalane, absence of C24 and C25 regular isoprenoids, 8-methyl-2-methyl-2-(4,8,12-trimethyltridecyl) chroman and C30 hop-17(21)-ene. Pyrolytic experiments showed that the sediments of the upper sequence, rich in aquatic OM, at a catagenetic stage could be a source of liquid hydrocarbons. The values of hopane, sterane and phenanthrene maturation parameters indicate that through pyrolysis at 400°C the samples investigated reached a value of vitrinite reflectance equivalent of approximately 0.70%. It was estimated that the sediments should be found at depths of 2300–2900 m in order to become active source rocks. The calculated minimum temperature, necessary for catagenetic hydrocarbon generation, is between 103 and 107°C.