Ivan Rakovec Institute of Palaeontology

Ljubljana, Slovenia

Ivan Rakovec Institute of Palaeontology

Ljubljana, Slovenia
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Sebela S.,ZRC SAZU | Zupancic N.,Ivan Rakovec Institute of Palaeontology | Miler M.,Geological Survey of Slovenia | Grcman H.,Biotechnical Faculty
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2017

Black deposits covering speleothems, cave walls and floors in Postojna Cave and Predjama Cave (SW Slovenia), and charcoal found in soil outside the Postojna Cave, were studied in order to establish their origin and age. SEM/EDS analysis of these deposits from both caves indicated that they are charred plant remains, very similar to oxidised charcoal in soil. Stable carbon isotope δ13C values of -29.41‰ (Črna Jama, P1), -26.9‰ (Predjama), and -25.1‰ (charcoal in soil) confirm their origin from biomass burning. Radiocarbon dating from Postojna Cave (Črna Jama (P1) 8394±35calyrB.P. and Pisani Rov 8235±25calyrB.P.) suggests that the oldest analysed black deposits formed in the Early Holocene (Mesolithic). The age is consistent with soil charcoal found at 1m depth in the surrounding area. Black deposits from Predjama were dated to 4095±25calyrB.P. (Eneolithic) and were caused by burning fires at the cave entrance, as supported by archaeological remains. Prehistoric (2375±20calyrB.P.) charcoal from the upper part of the soil profile (0.5 to 0.6m) and historic (1240±29calyrB.P. or 745calyrCE) black deposits from Postojna Cave (Črna Jama, P2) are related to forest fires, which are most likely human-induced. We interpret the oldest dated black deposits in Postojna Cave as traces of Early Holocene natural forest fires, since fire activity inside Črna Jama and Pisani Rov is not supported by archaeological remains. Favourable cave entrance morphology and microclimate allowed smoke to enter the cave during the winter period and deposit on speleothems. But an anthropogenic cause of forest fires cannot be excluded, since there are well-documented Mesolithic archaeological cave sites located close to the area. The study shows that black deposits on speleothems in caves are an important palaeoenvironmental record and proxy for Holocene climate. © 2017 Elsevier B.V.

Zupancic N.,University of Ljubljana | Zupancic N.,Ivan Rakovec Institute of Palaeontology | Miler M.,Geological Survey of Slovenia | Sebela S.,Karst Research Institute | Jarc S.,University of Ljubljana
Microscopy and Microanalysis | Year: 2016

Micro-scale observations in karst caves help to identify different processes that shaped local morphology. Scanning electron microscopy/energy-dispersive X-ray spectroscopy inspection of speleothems from two karst caves in Slovenia, Predjama and Črna Jama, confirmed the presence of sub-angular to sub-rounded detrital fragments of clay minerals, feldspars, quartz, Fe-oxides/hydroxides, rutile and Nb-rutile, xenotime, kassite, allanite, fluorapatite, epidote, ilmenite, monazite, sphene, and zircon, between 2 and 50 μm across. These occur in porous layers separating calcite laminae in the clayey coating on the layer below the surface of the speleothems, and are also incorporated within actual crystals. It is likely that they are derived from the weathered rocks of the Eocene flysch. Probably they were first transported into the caves by floodwaters forming cave sediments. Later, depending upon the climate conditions, they were moved by air currents or by water to the surface of active speleothems. They might also be redeposited from overlying soils enriched with wind-transported minerals from the flysch, or from higher passages filled with weathered flysch sediment, by drip water percolating through the fissured limestone. As some of the identified minerals are carriers of rare earth elements, Ti and Zr, their presence could affect any palaeoclimatic interpretations that are based upon the geochemical composition of the speleothems. © Microscopy Society of America 2016.

Skobe S.,University of Ljubljana | Gorican S.,Ivan Rakovec Institute of Palaeontology | Skaberne D.,Geological Survey of Slovenia | Verbic T.,Arhej d.o.o. | And 3 more authors.
Swiss Journal of Geosciences | Year: 2013

The study area in southeastern Slovenia is part of the transitional zone between the internal and the external Dinarides. Within Jurassic bedded cherts there are up to 2 cm thick shale intercalations, consisting of laminated, soft, fine-grained, green to brown material whose origin has been in question. In the majority of Tethyan cherts, the interbedded material is reported to be volcanogenic and/or terrigenous, although a detailed mineralogical analysis of the material is lacking. An XRD analysis confirmed the presence of quartz, illite, chlorite and K-feldspar, which is the prevailing component in some samples. Major and trace element data exclude both a volcanogenic and an hydrothermal origin. Several discrimination diagrams indicate the upper crustal terrigenous nature of shales and a biogenic silica source. The source material was probably from a Variscan crust, which at the time of deposition had already been weathered to kaolinite, and some sporadic muscovite. The MnO/Al2O3 ratio suggests a slow sedimentation rate of cherts and a faster one for shales, which probably settled from distal turbidity currents. The negative Ce anomaly indicates prolonged contact with ocean water. Sediments were deposited on a Tethyan passive margin, originally as silica-rich carbonate beds intercalated with mud. During late diagenesis, the mixing of marine and meteoric waters caused the further silicification of limestone and simultaneous potassium enrichment of shale which led to their alteration into illite or chlorite and, in sediments already rich in K-minerals, into K-feldspar. © 2013 Swiss Geological Society.

Jach R.,Jagiellonian University | Djeric N.,University of Belgrade | Gorican S.,Ivan Rakovec Institute of Palaeontology | Rehakova D.,Comenius University
Annales Societatis Geologorum Poloniae | Year: 2014

Middle-Upper Jurassic pelagic carbonates and radiolarites were studied in the Krížna Nappe of the Tatra Mountains (Central Western Carpathians, southern Poland and northern Slovakia). A carbon isotope stra- tigraphy of these deposits was combined with biostratigraphy, based on radiolarians, calcareous dinoflagellates and calpionellids. In the High Tatra and Belianske Tatra Mountains, the Bajocian and part of the Bathonian are represented by a thick succession of spotted limestones and grey nodular limestones, while in the Western Tatra Mountains by relatively thinBositra-crinoidal limestones. These deposits are referable to a deeper basin and a pelagic carbonate platform, respectively. The various carbonate facies are followed by deep-water biosiliceous facies, namely radiolarites and radiolarian-bearing limestones of Late Bathonian-early Late Kimmeridgian age. These facies pass into Upper Kimmeridgian-Lower Tithonian pelagic carbonates with abundantSaccocomasp. The bulk-carbonate isotope composition of the carbonate-siliceous deposits shows positive and negative δ13C excursions and shifts in the Early Bajocian, Late Bajocian, Early Bathonian, Late Bathonian, Late Callovian, Middle Oxfordian and Late Kimmeridgian. Additionally, the δ13C curves studied show a pronounced increasing trend in the Callovian and a steadily decreasing trend in the Oxfordian-Early Tithonian. These correlate with the trends known from the Tethyan region. The onset of Late Bathonian radiolarite sedimentation is marked by a decreasing trend in δ13C. Increased δ13C values in the Late Callovian, Middle Oxfordian and Late Kimmeridgian (Moluccana Zone) correspond with enhanced radiolarian production. A significant increase in CaCO3 content is recorded just above the Late Callovian δ13C excursion, which coincides with a transition from green to variegated radiolarites.

Crne A.E.,Ivan Rakovec Institute of Palaeontology | Weissert H.,ETH Zurich | Gorican S.,Ivan Rakovec Institute of Palaeontology | Bernasconi S.M.,ETH Zurich
Bulletin of the Geological Society of America | Year: 2011

Volcanic activity in the Central Atlantic magmatic province, resulting in an increased flux of CO2, SO2, and CH4 into the oceans and atmosphere, has been proposed as one of the mechanisms causing the biotic crisis at the Triassic-Jurassic boundary. Oceanic uptake of CO2 due to extreme greenhouse conditions should have had an impact on ocean chemistry and the position of the calcite compensation depth. In this study, we chose two pelagic sections from the Budva Basin as archives for paleoceanographic change across the Triassic-Jurassic boundary in deep-water settings. Our record represents the first documentation of a sudden termination of carbonate deposition across the Triassic-Jurassic boundary in a pelagic deep-water environment. Based on radiolarian biostratigraphy, the system boundary is placed at the sharp lithological contact between two pelagic formations, the Upper Triassic limestones and Lower Jurassic siliceous limestones alternating with shales. A rapid drop of carbonate content from 90% to less than 10% occurred contemporaneous with a negative anomaly in the stable carbon isotope record measured in both bulk carbonate (1.3‰) and bulk organic matter (1.1‰). The abrupt reduction of carbonate content in the Budva Basin was the result of either increased carbonate dissolution causing shoaling of the calcite compensation depth or reduced carbonate input due to biocalcification crisis. Both nonexclusive scenarios support the hypothesis of decreased ocean saturation with respect to calcium carbonate, which could be a direct consequence of increased CO2, SO2, and CH4 fluxes. © 2011 Geological Society of America.

Crne A.E.,Geological Survey of Norway | Crne A.E.,Ivan Rakovec Institute of Palaeontology | Melezhik V.A.,Geological Survey of Norway | Lepland A.,Geological Survey of Norway | And 5 more authors.
Precambrian Research | Year: 2014

The ca. 2.0 Ga Zaonega Formation in the Onega Basin of NW Russia represents a deep-water, mixed siliciclastic-carbonate depositional system with voluminous mafic volcanism. It is typified by extremely organic-rich rocks (TOC>40 wt%) and represents one of the earliest known episodes of oil/asphalt generation. These rocks have been inferred to archive one of the largest negative δ13C excursions in Earth history, one that followed and/or partially overlapped with the 2.2-2.06 Ga worldwide Lomagundi-Jatuli carbonate carbon isotopic excursion to high values and thought to be linked to the Paleoproteorozoic oxygenation of Earth's surface environments.In order to assess the post-depositional integrity of the carbonate carbon isotopic signal (δ13Ccarb) of the Zaonega rocks, we examined in detail the petrography and geochemistry of eight carbonate beds (0.3-0.9m thick) from different stratigraphic levels of the formation. The range of δ13C values for a single bed can be as much as 17‰, with calcite being significantly depleted in 13C relative to co-existing dolomite; the 13C-depleted calcite likely formed by involvement of carbon derived from diagenetic and catagenetic alteration of organic matter possibly abetted by volcanic CO2. The presence of calcite±talc±phlogopite±actinolite indicates metamorphic reaction of dolomite with quartz, or possibly K-feldspar, in the presence of water; commonly accompanied by degassing of 13C-enriched CO2, this caused further 13C depletion of newly formed calcite. The least altered dolomite is documented in central parts of thick dolostone beds with variably calcitized margins. This dolomite is considered as the earliest and possibly primary carbonate phase, potentially recording the δ13C signal of the ambient seawater. The least-altered dolomite is found in two stratigraphic intervals exhibiting δ13C values of +8 and +4‰ for the middle part of the formation, and δ13C values of -2 and -4‰ for the upper part. All other beds, with δ13C ranging from -19 to +3‰, are considered to have been variably depleted in their 13C content by post-depositional processes and therefore cannot be reliably used for assessing the carbon isotope composition of Paleoproterozoic seawater. Our results emphasize the importance of distinguishing primary versus secondary (or later) isotopic compositions in studies of carbonate rocks used for reconstruction of global environmental change. © 2013 Elsevier B.V.

Rich calcareous nannoplankton assemblages were recovered from the Badenian (Middle Miocene) in Slovenske gorice (Eastern Slovenia). Paleogeographically, the investigated area belonged to the Mura Depression, a heterogenous marginal basin of the Central Paratethys. Over one hundred species of calcareous nannoplankton were found in the Badenian marls, among them two new Pontosphaera species were determined and are described in this paper. The nannoplankton assemblages, containing specimens of Pontosphaera geminipora n. sp. and Pontosphaera desuetoidea n. sp., allow their assignment to the standard nannoplankton biozone NN5. Both species are rare and occur in diverse assemblages, indicating warm and stable, relatively deep and oligotrophic depositional environments.

Bartol M.,Ivan Rakovec Institute of Palaeontology | Mikuz V.,Ivan Rakovec Institute of Palaeontology | Horvat A.,Ivan Rakovec Institute of Palaeontology
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014

In the Middle Miocene the area of present-day eastern Slovenia was situated at the eastern mouth of the Slovenian Corridor - a hypothetical seaway connecting the Central Paratethys and the Mediterranean. The exact location and time of closure of a seaway between the two neighbouring marine realms are still a matter of debate. We studied Badenian (late Langhian and early Serravallian) calcareous nannoplankton assemblages from eastern Slovenia for their palaeogeographical significance by comparing them to contemporaneous Central Paratethyan and Mediterranean assemblages and the assemblages described in selected ODP and IODP reports. Assemblage composition and the sequence of biostratigraphic events observed in Slovenia were very similar to that in several Mediterranean sites. Comparison with the World Ocean suggests that this similarity reflects communication between the Mediterranean and Paratethyan populations rather than a universal trend of nannoplankton evolution.Late Badenian assemblages from different localities within the Central Paratethys exhibit considerable variation with respect to the presence of discoasters (considered as typical of the Mediterranean) and the presence of Rhabdosphaera poculi and Hayella challengeri (considered as typical of the Eastern Paratethys). Our results suggest the mixing of Mediterranean and Eastern Paratethyan influences throughout the entire Central Paratethys during the late Badenian. The observed variability explains how opposing views on the status of the marine connection between the Central Paratethys and the Mediterranean in the late Badenian can arise from palaeontological studies of fossil assemblages considering only a single site or a small area.The gastropod species Pereiraea gervaisi migrated from the Mediterranean to the Central Paratethys - where it is only known from the immediate proximity of the hypothesised Slovenian Corridor. This supports the thesis that the communication between the two seas took place via the Slovenian Corridor and not some other marine connection like the hypothetical Axios (Vardar) Trench. © 2013 Elsevier B.V.

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