Time filter

Source Type

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

Discover hidden collaborations