Boštjan Rožič

Integrated Rhaetian foraminiferal and conodont biostratigraphy from the Slovenian Basin, eastern Southern Alps

Conodonts and re-deposited shallow-water benthic foraminifera co-occur in the Upper Norian-Rhaetian Slatnik Formation of the Slovenian Basin (Southern Alps). The Mt. Kobla and Mt. Slatnik sections were investigated in order to give the first direct correlation between these two groups. The Norian-Rhaetian boundary (NRB) is placed at the First Appearance Datum of the conodont Misikella posthernsteini and is approached with the First Occurrence of the foraminifer Involutina turgida. An association of Trocholina turris with duostominids is a good marker for the Rhaetian. Careful revision of literature combined with our data culminated in reambulation of stratigraphical ranges for several foraminiferal species. The foraminiferal Triassic-Jurassic boundary (TJB) can be defined with the Last Occurrence of Galeanella tollmanni, “Sigmoilina” schaeferae or duostominids. The absence of the uppermost Rhaetian Misikella ultima conodont zone and the close coincidence of foraminiferal and conodont TJB could point to the presence of hiati in the upper part of the Slatnik Formation. Consequently, the exact pattern of disappearance of Late Triassic foraminifera at the boundary could not be observed. It is clear, however, that the foraminiferal assemblage was decimated for reef-dwelling foraminifera, duostominids and most of the platform-dwelling foraminifera. Biotic changes at the TJB are best explained as a result of a biocalcification crisis.

Carnian reefal blocks in the Slovenian Basin, eastern Southern Alps

The Carnian Amphiclina beds of the eastern Southern Alps mostly consist of shale and sandstone deposited in the deep-marine Slovenian Basin, which was located near the western margin of the Meliata Ocean. In the vicinity of Cerkno (Slovenia), blocks of massive or crudely bedded limestone crop out within a succession of clastic rocks that are several hundred meters thick. Sponge-microbialite boundstone and coral pillarstone are the predominant facies within these blocks. Oncoid floatstone-rudstone and moderately sorted peloid packstone form crudely layered parts of the blocks, whereas intraclast-cortoid packstone and poorly sorted peloid packstone occur locally in cross-stratified thin beds, truncated at block margins. Detailed mapping further shows that limestone blocks form units at discrete stratigraphic levels within shale and that these units are variable in thickness. Whereas the largest blocks mostly lie concordant to the bedding, smaller blocks are poorly sorted and randomly oriented. All of this evidence suggests that the limestone blocks are olistoliths, derived from an outer platform margin and/or uppermost slope.

Podpeč limestone: a heritage stone from Slovenia

Abstract Podpeč Limestone is characterized by its dark grey or nearly black colour, contrasting with white fossil shells of the mollusc Lithiotis. This formation, which has been dated as Lower Jurassic, occurs in southern and southwestern Slovenia and is particularly conspicuous in areas SW of Ljubljana. The main quarry, which is not active, is located near the village of Podpeč near Ljubljana and has been recognized as a geological site of national importance; as such, it is officially protected as a natural monument. The utilization of Podpeč Limestone was first documented during the Roman period in Slovenia. At the end of the 5th century AD, with the decline of the Roman Empire, stone-cutting ceased at Podpeč for many centuries. Towards the end of the 19th century Podpeč Limestone became better-known. During the first half of the 20th century significant stonecutting workshops were established in Podpeč with most stone being supplied from the main quarry. The internationally renowned Slovenian architect Jože Plečnik (1872–1957) used Podpeč Limestone in various Slovenian buildings, some of national importance. The utilization and national recognition of Podpeč Limestone within Slovenia provide abundant support for its nomination as a Global Heritage Stone Resource.

FIRST EVIDENCE FOR LATE NORIAN PROGRADATION OF JULIAN PLATFORM TOWARDS SLOVENIAN BASIN, EASTERN SOUTHERN ALPS

The Late Triassic in the Southern Alps is marked by an extensive growth of carbonate platforms. Whereas Dolomia Principale dominates the western and central sections, Dachstein Limestone dominates the eastern side of the Southern Alps on the so-called Julian Platform in what is now NW Slovenia. Younger tectonic movements greatly deformed the original configuration of the Julian Platform and its margins are consequently poorly preserved. While late Tuvalian and early Norian platform progradation has been recorded on the northern and eastern side of the platform, no such information is available for the southern edge of the platform, where it borders the deeper Slovenian Basin. Three detailed sedimentological sections from the southern slopes of the Jelovica plateau span from the top of the basinal Baca dolomite to the Slatnik Formation and the prograding slope of the Dachstein Limestone. The progradation has been dated as late Norian in age, and can be correlated to a poorly-expressed coarsening event recorded in previously known sections of the Slovenian Basin. In contrast to deeper parts of the basin, shallow water conditions were established on the Jelovica plateau by the beginning of the Rhaetian.

Sedimentary record of subsidence pulse at the Triassic/Jurassic boundary interval in the Slovenian Basin (eastern Southern Alps)

Abstract In the Alpine Realm the Early Jurassic is characterized by the disintegration and partial drowning of vast platform areas. In the eastern part of the Southern Alps (present-day NW Slovenia), the Julian Carbonate Platform and the adjacent, E-W extending Slovenian Basin underwent partial disintegration, drowning and deepening from the Pliensbachian on, whereas only nominal environmental changes developed on the large Dinaric (Friuli, Adriatic) Carbonate Platform to the south (structurally part of the Dinarides). These events, however, were preceded by an earlier - and as yet undocumented extensional event - that took place near the Triassic/Jurassic boundary. This paper provides evidence of an accelerated subsidence from four selected areas within the Slovenian Basin, which show a trend of eastwardly-decreasing deformation. In the westernmost (Mrzli vrh) section - the Upper Triassic platform-margin - massive dolomite is overlain by the earliest Jurassic toe-of-slope carbonate resediments and further, by basin-plain micritic limestone. Further east (Perbla and Liščak sections) the Triassic-Jurassic transition interval is marked by an increase in resedimented carbonates. We relate this to the increasing inclination and segmentation of the slope and adjacent basin floor. The easternmost (Mt. Porezen) area shows a rather monotonous, latest Triassic-Early Jurassic basinal sedimentation. However, changes in the thickness of the Hettangian-Pliensbachian Krikov Formation point to a tilting of tectonic blocks within the basin area. Lateral facies changes at the base of the formation indicate that the tilting occurred at and/or shortly after the Triassic/Jurassic boundary

THE MIDDLE JURASSIC TO LOWER CRETACEOUS SUCCESSION OF THE PONIKVE KLIPPE: THE SOUTHERNMOST OUTCROPS OF THE SLOVENIAN BASIN IN WESTERN SLOVENIA

The Slovenian Basin was a Mesozoic deep-water paleogeographic domain located north of the Dinaric Carbonate Platform. Due to a considerable amount of southward-directed thrusting and subsequent erosion, the marginal parts of this basin are only sparsely preserved. The southernmost remains of the Slovenian Basin in western Slovenia are found in the Ponikve Klippe, where we studied a Middle Jurassic (? Aalenian) to Lower Cretaceous (Albian) succession. We dated the succession with radiolarians, calpionellids, and benthic foraminifers. The succession is divided into three formations. The first is the Middle Jurassic to Lower Tithonian Tolmin Formation, composed of radiolarian cherts, siliceous limestone, and calciturbidites. The second formation is the Upper Tithonian–Berriasian Biancone limestone, which consists of pelagic limestone with calpionellids and one interstratified calciturbidite. The third formation, the Lower flyschoid formation, rests upon a prominent, regionally recognized erosional unconformity. The formation begins with calcareous breccia and continues with finer-grained calciturbidites that alternate with marl/shale and chert. Only the lower part of this formation was investigated and dated to the late Aptian to early Albian. The correlation of the studied section with the previously described successions of the Slovenian Basin shows that the Jurassic part of the section clearly exhibits a more marginal setting, whereas the Cretaceous part of the section correlates well with the central basinal succession. This inversion was related to the late Aptian tectonic event that was also responsible for the considerable submarine erosion and deposition of the basal breccia of the Lower flyschoid formation.

Middle Jurassic limestone megabreccia from the southern margin 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 Karst Region of Slovenia: A Potential Global Heritage Stone Province

The Karst (Kras) region of Slovenia is one of the world’s most interesting areas of natural stone reserves. The region is mainly composed of Cretaceous shallow-water limestone, with the most common type currently excavated being the rudist limestone of the Lipica Formation, which date to the Santonian to Campanian times. The Karst region has been associated with the quarrying and processing of stone for over two thousand years, i.e. since the Roman period. The exploitation and international recognition of the Karst region provide abundant support for its nomination as a Global Heritage Stone Province.