In the southernmost outcrops of the Slovenian Basin the Middle Jurassic coarse-grained limestone breccia (mega)beds are interstratified within a succession that is otherwise dominated by ...hemipelagites and distal turbidites. In this paper, these beds are described as the Ponikve Breccia Member of the Tolmin Formation. We provide descriptions of the studied sections with detailed geological maps and analysis of the breccia lithoclasts. From the latter, a non-outcropping margin of the Dinaric Carbonate Platform is reconstructed. In the Late Triassic the platform margin was characterized by a Dachstein-type marginal reef. After the end-Triassic extinction event, the platform architecture remained, but the reefs were replaced by sand shoals characterized by ooids. In the late Early Jurassic and/or early Middle Jurassic a slope area might have been dissected by normal faults and a step-like paleotopography was formed. In the Bajocian, during a period of major regional geodynamic perturbations, extensional or transtensional tectonic activity intensified and triggered the large-scale collapses of the Dinaric Carbonate Platform margin producing the limestone breccias described herein. This may in turn have caused a backstepping of the platform margin, as is evident from the occurrence of Late Jurassic marginal reefs that are installed directly above the Upper Triassic and Lower Jurassic inner platform successions.
The area between the villages of Reka in the Idrijca Valley, Bukovo and Zakriž near Cerkno belongs geographically and geotectonically to the Dinarides. The area consists of two large inner thrust ...blocks of the Trnovo nappe, which were thrusted for tens of kilometers in the direction of SW to their present position. They are overlain by the Tolmin nappe, the lowest thrust unit of the Southern Alps. The Tolmin nappe was thrusted from N to S and consists of two inner thrust blocks and a smaller intermediate inner sheet. In the western part of the area the contact between Southern Alps and the Dinarides runs along the regional Sovodenj fault. Although the rocks in the considered thrust units are about the same age, different stratigraphic settings could be recognized. The lithostratigraphic features of the Ladinian-Lower Carnian Pseudizilian beds are particularly striking. Succession of clastic and carbonate rocks was deposited in deep-marine Slovenian basin. In both the Trnovo and Tolmin nappe, Pseudozilian beds occur in the lithologically characteristic sequences but, in the Tolmin nappe, they are developed in a much greater thickness than in the Trnovo nappe and pass continuously upwards into Amphyclina beds, while in the Trnovo nappe, on the other hand, the succession of Pseudozilian beds is much thinner and is overlain by the platform Cordevol dolomite.
The evolution of the Slovenian Basin southern margin is currently interpreted based on the successions outcropping in the surroundings of Škofja Loka, on the Ponikve Plateau and in the foothills of ...the Julian Alps in western Slovenia, as well as from the valley of the Mirna River in south-eastern Slovenia. However, no extensive research on this paleogeographic unit has been carried out in the northern part of the Sava Folds region. Recent field observations permitted the recognition of Upper Triassic to lowermost Cretaceous successions of the Slovenian Basin, including the recently described Middle Jurassic Ponikve Breccia Member of the Tolmin Formation. Based on reambulation-type geological mapping, macroscopic facies observations supported by microfacies analysis and biostratigraphy, three stratigraphic columns were constructed showcasing Slovenian Basin formations on the northern flank of the Trojane Anticline (Sava Folds region). These newly described successions encompass Upper Triassic (Bača Dolomite Formation) and Jurassic–lowermost Cretaceous resedimented limestones and pelagic formations, while the attribution of the Pseudozilian Formation is complex. Based on facies characteristics these successions are similar to those preserved in the Podmelec Nappe (lowermost thrust unit of the Tolmin Nappe) in western Slovenia. The connection between the western and the eastern Slovenian Basin during the Late Triassic-Early Cretaceous interval could be thus recognised.
The research area is located in south-eastern Slovenia and belongs to the eastern extensions of the Slovenian Basin adjacent to the Adriatic Carbonate Platform. The studied section is 25 m thick and ...consists of grey, brownish and reddish pelagic limestones and calciturbidites, and two bentonite layers 110 and 10 cm thick. Both volcanoclastic horizons consist of greenish, fine-grained muddy material. To date, no other bentonites of similar age are known in the wider Southern Alpine and Dinaridic region. The late Campanian to Campanian/Maastrichtian age of the succession was determined from planktonic foraminifera and calcareous nanoplankton assemblages. XRD analysis revealed the presence of calcite, quartz, muscovite/illite and smectite, which prevails in the clay fraction and is indicative of bentonite clays. We interpret these bentonite horizons as resulting from direct deposition of volcanic ash in a marine environment with a concomitant admixture of detrital material (quartz, muscovite) and later diagenetic carbonatization. The geochemical composition suggests a felsic volcanic origin. The most likely source is the Late Cretaceous–Paleogene bimodal rhyolitic/basaltic volcanism documented along the Sava Suture Zone in present-day Croatia, Bosnia and Herzegovina, Serbia, and North Macedonia. In the Central Apennines three locations with bentonites have been documented. Further spatial and temporal analysis of similar volcanogenic horizons could yield important data on the paleogeographic and tectonic evolution of the Adria/Apulia continental margin.
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•Important discovery of upper Campanian bentonite layers on the eastern Adria margin.•Volcanic ash deposition in a deeper-marine, carbonate dominated environment.•Correlates with Campanian rhyolitic volcanic activity in the Sava Suture Zone.
This study presents the results of the conodont biostratigraphy and microfacies analysis carried out on the pelagic limestones of the Upper Triassic Dovško Section in Slovenia, which represents the ...eastern part of the Slovenian Basin. The age of the section ranges from the Lacian 1 to the Alaunian 1. The Lacian part of the succession is predominantly characterized by the representatives of the genus
Ancyrogondolella
. Transitional morphologies towards Alaunian faunas first appear in the Lacian 3 and become common during the Lacian-Alaunian transition. This evolutionary development coincides with a shift in microfacies from a dominantly radiolarian-bearing mudstone-wackestone-packstone to a filament- dominated wackestone-packstone, and the formation of small neptunian dykes, which may reflect environmental perturbations and/or a change in basin geometry. The proliferation of the genera
Epigondolella
and
Mockina
is observed in the Alaunian part of the section, though the genus
Ancyrogondolella
is still present in this interval. Systematic description of the conodont taxa is provided, and seven new species and two new subspecies are established. The new advances will be of great value in further biostratigraphic studies, especially in areas without ammonoid faunas, and in the reconstruction of the paleogeography of the Slovenian Basin.
The Slovenian Basin is a Mesozoic deep-water paleogeographic unit, located along the border between the eastern Southern Alps and the Dinarides, that records geodynamic signals from the opening of ...both the Piedmont-Liguria and the Neotethys oceanic domains. In the Middle Jurassic, it was bordered by the Dinaric (Adriatic) Carbonate Platform to the south and the Julian High submarine plateau to the north. The southern margin of the basin is characterized by a several tens of meters thick sedimentary sequence of Bajocian-Bathonian (Callovian?) age that is dominated by limestone megabreccia shed from the Dinaric Carbonate Platform, sedimented by debris-flows in a toe-of-slope sedimentary environment. It is accompanied by rud/grain/packstone beds sedimented via (high-density) turbidity-flows. This megabreccia unit represents the proximal equivalent of the lower resedimented limestones of the Tolmin Formation. The matrix within lithoclasts indicates resedimentation from ooidal shoals and the erosion of basinal and slope sediments. Lithoclasts are of Norian to Lower Jurassic age, and originated from (A) platform margin carbonates, i.e. Triassic marginal reef and Lower Jurassic sand-shoal limestones, (B) deep open-shelf or slope coarse bioclastic limestones, and (C) older basinal rocks. The lithoclast analysis enables the reconstruction of the platform-basin transitional zone that is not preserved (exposed) due to overthrusting. The limestone megabreccia indicates enhanced tectonic activity causing repeated collapse of the platform margin, probably connected to the initiation of intraoceanic subduction within Neotethys followed by ophiolite obduction onto the eastern distal margin of the Adria.
The village of Crngrob (central Slovenia) is known to geologists for the silicifid fossils found in the thick soil covering the “Amphiclina beds”, a Carnian lithostratigraphic unit of the Mesozoic ...Slovenian Basin. Due to silicifiation, the assemblage may provide an important insight into Carnian marine life; however, the nature of the fossil assemblage, as well as the timing and mode of silicifiation are unknown. A detailed sedimentological section, which covers the uppermost part of the “Amphiclina beds” and their transition to the “Bača Dolomite”, was recorded at one of the fossil-bearing localities. The section consists of limestone (including bioturbated fiament and radiolaria-fiament wackestones, laminated fiament packstone, bioclast wackestone, peloid packstone, flatstone with intraclasts and bioclasts, and intraclast flatstone and rudstone), marlstone and dolomite. Chert is locally present in nodules or as dispersed silicifid patches, giving a speckled appearance to the host rock. According to our interpretation, the deposition of the limestone occurred via hemipelagic settling, turbidite currents and debris flws in a slope-to-basin or outer ramp setting. The composition of the grains (which include green algae fragments, thick-shelled bivalves, corals and solenoporacean algae) clearly points to the allochthonous nature of the material, which was largely derived from shallow-water environments. Fossils, as well as the intraclasts and sometimes the matrix, are locally replaced by chalcedony and granular megaquartz. This type of silicifiation does not appear to be selective to particular microfacies. As the silicifiation occurred after the down-slope transport of shells and the deposition of the sediment, the Crngrob fossil assemblage represents a thanatocoenosis or even a taphocoenosis, and it is not representative of autochthonous Carnian associations.
The Alpine–Dinaric Transition Zone in Slovenia comprises the fold and thrust belt of the Southern Alps (South Karawanken Range, Julian Alps), Slovenian Basin and the Dinarides. The Slovenian Basin ...located between the Julian and Dinaric carbonate platforms evolved during Middle Triassic time and remained in a deep marine setting till the Late Cretaceous. The thermal history of Carboniferous to Eocene rocks in that area was investigated using vitrinite reflectance (VR) data, apatite fission track analysis and numeric 1D basin modeling. The study shows that maturity patterns are mainly controlled by the thickness of Upper Cretaceous to Eocene flysch deposits, filling the accommodation space. Therefore the thermal overprint reaches a maximum (>4%Rr) in Triassic to Cretaceous sediments of the Slovenian Basin and decreases towards the north and south. Minor sedimentary burial of the Adriatic Carbonate Platform and the Julian Alps results in a lower thermal overprint (<1.5%Rr). The thickness of flysch sediments was about 5km in the area of the Sava Folds, but significantly higher in the central part of the Slovenian Basin. Heat flow during maximum burial in Eocene time was in the order of the global average (60mW/m2). Cooling of Paleozoic and Mesozoic sediments below 110°C occurred between Late Eocene and Early Oligocene times in different parts of the study area. Nappe stacking due to Early (Dinaric) and Late Cenozoic (Alpine) compressional tectonics did not influence the thermal maturity of the sediments.
•Maturity of Mesozoic rocks in the Alpine-Dinaric transition zone is controlled by thickness of Cretaceous to Paleogene rocks.•Highest maturity is observed in the Slovenian Basin.•High vitrinite reflectance in Cretaceous sediments (up to 4.4 %Rr) is due to very thick Paleogene flysch sediments.•Uplift and cooling occurred between Late Eocene and Mid Oligocene time.•Thrusting postdates maturation.
Decapod associations have been significant components of marine habitats throughout the Cenozoic when the major diversification of the group occurred. In this respect, the circum-Mediterranean area ...is of particular interest due to its complex palaeogeographic history. During the Oligo-Miocene, it was divided in two major areas, Mediterranean and Paratethys. Decapod crustaceans from the Paratethys Sea have been reported in the literature since the 19
century, but only recent research advances allow evaluation of the diversity and distribution patterns of the group. Altogether 176 species-level taxa have been identified from the Oligocene and Miocene of the Western and Central Paratethys. Using the three-dimensional NMDS analysis, the composition of decapod crustacean faunas of the Paratethys shows significant differences through time. The Ottnangian and Karpatian decapod associations were similar to each other both taxonomically and in the mode of preservation, and they differed taxonomically from the Badenian ones. The Early Badenian assemblages also differed taxonomically from the Late Badenian ones. The time factor, including speciation, immigration from other provinces and/or (local or global) extinction, can explain temporal differences among assemblages within the same environment. High decapod diversity during the Badenian was correlated with the presence of reefal settings. The Badenian was the time with the highest decapod diversity, which can, however, be a consequence of undersampling of other time slices. Whereas the Ottnangian and Karpatian decapod assemblages are preserved virtually exclusively in the siliciclastic “Schlier”-type facies that originated in non-reefal offshore environments, carbonate sedimentation and the presence of reefal environments during the Badenian in the Central Paratethys promoted thriving of more diverse reef-associated assemblages. In general, Paratethyan decapods exhibited homogeneous distribution during the Oligo-Miocene among the basins in the Paratethys. Based on the co-occurrence of certain decapod species, migration between the Paratethys and the North Sea during the Early Miocene probably occurred via the Rhine Graben. At larger spatial scales, our results suggest that the circum-Mediterranean marine decapod taxa migrated in an easterly direction during the Oligocene and/or Miocene, establishing present-day decapod communities in the Indo-West Pacific.
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