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Gorican S.,Ivan Rakovec Institute of Paleontology | Pavsic J.,University of Ljubljana | Rozic B.,University of Ljubljana
Bulletin de la Societe Geologique de France | Year: 2012

The Tolmin basin is a typical example of a deep-water Mesozoic basin that developed on the rifted south Tethyan continental margin. Remnants of this basin are preserved at the intersection of the Dinarides and the southern Alps in northwestern Slovenia. The Jurassic successions consist of carbonate gravity-flow deposits, radiolarian cherts and shales, and are overlain by pelagic Biancone limestone. A distinctive chert-dominated interval (the upper member of the Tolmin Formation) was dated with radiolarians. The base of this interval was assigned to the late Bajocian in the distal part of the basin and to the middle Callovian-early Oxfordian in the more proximal part of the basin. The topmost radiolarian cherts are early Tithonian in age. The mid-Tithonian transition from chert to the Biancone limestone was also determined with nannoplankton. The beginning of highly siliceous sedimentation in the Bajocian correlates well over the entire western Tethys and was linked to two factors: an increase in water depth due to regional subsidence and an increase in plankton productivity. The pronounced silica enrichment coincided with the opening of the Alpine Tethys and with the intraoceanic subduction that occurred in the Meliata-Maliac-Vardar Ocean. Reorganization of the plate boundaries may have induced substantial changes in the circulation of water masses that, in turn, had a long-term effect on surface productivity. On the basin scale, radiolarian dating revealed considerable lateral and vertical variations in the thickness of chert successions. This distributional pattern implies that, in narrow continental-margin basins, sedimentation rates were primarily determined by the redeposition of pelagic sediments. Important stratigraphie gaps occur even in the distal basinal setting.

Krische O.,Haritzmeierstrae 12 | Gorican S.,Ivan Rakovec Institute of Paleontology | Gawlick H.-J.,Peter Tunner Strae
Geologica Carpathica | Year: 2014

The microfacies and biostratigraphy of components in mass-flow deposits from the Lower Cretaceous Rossfeld Formation of the Northern Calcareous Alps in Austria were analysed. The pebbles are classified into six groups: 1) Triassic carbonates (uppermost Werfen to basal Gutenstein Formations), 2) Upper Jurassic to lowermost Cretaceous carbonates (Oberalm Formation and Barmstein Limestone), 3) contemporaneous carbonate bioclasts (Valanginian to ?Hauterivian), 4) siliceous pebbles (radiolarites, ophicalcites, siliceous deep-sea clays, cherts), 5) volcanic and ophiolitic rock fragments and 6) siliciclastics such as quartz-sandstones and siltstones. The radiolarites show three age groups: Ladinian to Early Carnian, Late Carnian/Norian and Late Bajocian to Callovian. The Middle Triassic radiolarites are interpreted as derived from the Meliata facies zone or from the Neotethys ocean floor, whereas the Late Triassic radiolarites give evidence of the sedimentary cover of the Neotethys ocean floor. During late Early to early Late Jurassic, the Triassic to Early/Middle Jurassic passive margin of the Neotethys attained a lower plate position and became obducted by the accreted ocean floor of the Neotethys Ocean. The accreted ocean floor was contemporaneously eroded and resedimented in different deep-water basins in front of the nappe-stack. These basin fills were subsequently incorporated in the orogen forming mélanges in this complex ophiolitic nappe-stack. The Middle Jurassic radiolarites are interpreted as the matrix of these mélanges. Together with the volcanic and ophiolitic material the siliceous rocks were eroded from this ophiolitic nappe-stack in Early Cretaceous times and brought by a fluvial system to the Rossfeld Basin within the Tirolic realm of the Northern Calcareous Alps. The different fining-upward sequences in the succession of the Lower Cretaceous Rossfeld Formation can be best explained by sea-level fluctuations and decreasing tectonic activity in the Jurassic orogen.

Lepland A.,Geological Survey of Norway | Lepland A.,Tallinn University of Technology | Lepland A.,University of Tromsø | Joosu L.,University of Tartu | And 15 more authors.
Nature Geoscience | Year: 2014

All known forms of life require phosphorus, and biological processes strongly influence the global phosphorus cycle. Although the record of life on Earth extends back to 3.8 billion years ago and the advent of biological phosphate processing can be tracked to at least 3.5 billion years ago, the earliest known P-rich deposits appeared only 2 billion years ago. The onset of P deposition has been attributed to the rise of atmospheric oxygen 2.4-2.3 billion years ago and the related profound biogeochemical shifts, which increased the riverine input of phosphate to the ocean and boosted biological productivity and phosphogenesis. However, the P-rich deposits post-date the rise of oxygen by about 300 million years. Here we use microfabric, trace element and carbon isotope analyses to assess the environmental setting and redox conditions of the 2-billion-year-old P-rich deposits of the vent-or seep-influenced Zaonega Formation, northwest Russia. We identify phosphatized microorganism fossils that resemble modern methanotrophic archaea and sulphur-oxidizing bacteria, analogous to organisms found in modern seep settings and upwelling zones with a sharp redoxcline. We therefore propose that the P-rich deposits in the Zaonega Formation were formed by phosphogenesis mediated by sulphur bacteria, similar to modern sites, and by the precipitation of calcium phosphate minerals on microbial templates during early diagenesis. © 2014 Macmillan Publishers Limited.

Celarc B.,Geological Survey of Slovenia | Gorican S.,Ivan Rakovec Institute of Paleontology | Kolar-Jurkovsek T.,Geological Survey of Slovenia
Facies | Year: 2013

In the Julian Alps (Mt. Prisojnik, NW Slovenia) and in the Kamnik-Savinja Alps (Mt. Križevnik, N Slovenia), both of which form part of the eastern Southern Alps, several meters of Upper Anisian pelagic red nodular, radiolarian-rich limestone (Loibl Formation) were deposited on the drowned platform carbonates of the Contrin Formation. The time of the platform drowning is dated with radiolarians and conodonts to the Illyrian, more precisely to the upper part of the Paraceratites trinodosus Ammonoid Zone. The red limestone is overlain by pyroclastics and volcanics (rhyolites) or carbonate (mega)breccia (Uggowitz Formation). The following unit consists of thin-bedded limestone, grainstone and subordinate marl (Buchenstein Formation) deposited during the final filling of the basin from the adjacent prograding carbonate platform (Schlern Formation) in the Ladinian. Map-scale geometry, neptunian dykes, the onset of volcanism, the presence of (mega)breccia and related paleo-escarpments, the lateral variations in thickness and the wedge-shaped geometry of the lithological units provide evidence of syn-sedimentary block faulting and the formation of small-scale, relatively shallow half-grabens within the previously uniform Slovenian Carbonate Platform. This analysis indicates a clear tectonic control over the development of the Middle Triassic stratigraphy. The described extensional event is well correlated and genetically connected with the syn-rift formation of the neighboring Slovenian Basin and other Southern Alpine basins that formed in connection with the opening of the Meliata-Maliac branch of the Neotethys Ocean. © 2012 Springer-Verlag.

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