Jasenka Sremac

Late Variscan (Carboniferous to Permian) environments in the Circum Pannonian Region

Late Variscan (Carboniferous to Permian) environments in the Circum Pannonian Region The Pennsylvanian-Cisuralian late-orogenic and post-orogenic paleoenvironments of the Circum Pannonian Region (CPR) include tectono-stratigraphic sequences developed from the Upper Bashkirian-Moscovian marine early molasse stage up to the Guadalupian-Lopingian post-orogenic stage, with gradual connection to the beginning of the Alpine (Neotethyan) sedimentary cycle. Shallow marine siliciclastic or carbonate siliciclastic overstep sequences started in the internal part of the Variscan orogenic belt during the latest Serpukhovian and Bashkirian-Moscovian. They overlapped unconformably the variably metamorphosed Variscan basement, or weakly deformed and metamorphosed foreland and syn-orogenic flysch sediments of Mississippian to Early Pennsylvanian age. The post-Variscan rifting largely affected the Variscan orogenic belt by reactivation of the Variscan lithosphere. The late- to post-orogenic terrestrial sequences started within the internal part of the Variscan orogenic belt during the Middle/Late Pennsylvanian. It continued gradually to terrestrial-shallow water carbonate-siliciclastic sequences in its external part through the Permian. According to the present configuration, the Alpine (Neotethyan) northward shifting transgression started during the Guadalupian/Lopingian in the South and during the Early Triassic in the North.

Equatorial Shelf of the Palaeozoic Supercontinent - Cradle of the Adriatic Carbonate Platform

During the Carboniferous and Permian, several carbonate platforms existed along the eastern coast of the supercontinent Pangaea. Croatian Palaeozoic carbonate sediments were produced in this “carbonate factory”. The dominant skeletal carbonate producers were calcareous algae, with assistance from foraminifera, molluscs, brachiopods and crinoids. Sporadically, reef structures were built by calcisponges, bryozoans, algal and cyanobacterial encrusters. Variscan and post-Variscan tectonic events strongly influenced the platform existence through uplift and deposition of molasse sediments, while a global catastrophe at the Permian/Triassic boundary only changed the biotic carbonate producers. A significant input of terrestrial material during the Lower Triassic, due to uplift and/or global regression, altered the mode of sedimentation along the shallow Palaeotethyan shelves. Platforms were partly restored during the Middle and Upper Triassic, and existed with short interruptions till the Middle Eocene.

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia)

Early Miocene ostracods from the Sadovi section (Mt Požeška gora, Croatia) The study of the Early Miocene (Late Ottnangian/Early Karpatian) ostracod fauna from the Sadovi section (Mt Požeška gora, Croatia) led to several results concerning Neogene paleobiogeography and paleoecology. Brackish deposits of Late Ottnangian and Early Karpatian age have been recognized for the first time in the North Croatian Basin. These deposits indicate the first marine ingression into the Early Miocene lake in this area. Twenty-nine ostracod species were determined, including the new taxa Fabaeformiscandona slavonica nov. sp. and Herpetocypris sadovii nov. sp.

Palaeoecology of the Late Badenian foraminifera and ostracoda from the SW Central Paratethys (Medvednica Mt., Croatia)

The quantitative study of microfossil communities from the Late Badenian marls at the Sveta Barbara locality (eastern Medvednica Mt.) enabled reconstruction of three different palaeoenvironments: middle shelf, outer shelf and upper bathyal. The dominant factors influencing the distribution of biota were the deepening of the depositional basin and fluctuations of the oxygenation rate. The outer shelf biota existed under conditions of decreased oxygen levels in bottom water, compared to communities from the middle shelf and upper bathyal environments.

New Congerian Species and Their Similarity with Congeria banatica from the Pannonian Sediments in Northern Croatia

Congeria baschi n.sp. and Congeria susedana n.sp. are two new species from the Pannonian sediments of the Medvednica Mts. (NW Croatia). C. baschi n. s p . was found in the Lower Pannonian limestones, and C. susedana n.s p . was collected from the Upper Pannonian marls. Relationships with the affiliated taxa enable reconstruction of a phyletic lineage beginning with Congeria soceni JEKELIUS, through C. baschi n.sp. to Congeria banatica HORNES. C. banatica is the ancestor of two branches, leading to C. susedana n. sp. and C. vugro veci SREMAC, respectively. Dreissenomya digitifera (ANDRUSOV) is the probable descendant of C. vugroveci. The accompanying assemblages of fossil molluscs and ostracods from the same horizons facilitate the precise stratigraphic and palaeoenvironmental positioning of the new taxa.

Permian deposits and the Permian–Triassic boundary in Croatia: palaeoclimatic implications based on palaeontological and geochemical data

Abstract The Late Palaeozoic deposits in Croatia were derived from the Palaeotethyan shelf areas along the northern Gondwana passive continental margin and consist of mixed carbonate–clastic facies. These sedimentary rocks accumulated in the equatorial area along northern Gondwana under a dominantly hot climate and laid the foundations for the future Adriatic Carbonate Platform (AdCP). Detailed classification and geochemical studies of the Permian and Permian–Triassic deposits in most parts of Croatia are still in progress, especially concerning palaeoclimate and regional palaeogeography. The best preserved Permian outcrops can be found in the Velebit mountain area, including continuous Permian–Triassic sections. Stable isotopes of carbon and oxygen from carbonates, with characteristic positive δ13Ccarb excursion during the Late Permian and negative δ13Ccarb excursion at the Permian–Triassic transition combined with palaeontological and sedimentological data, helped in palaeoclimate estimations and the positioning of the chemostratigraphical Permian–Triassic Boundary (PTB). Sedimentological, palaeontological and geochemical data indicate that deposition in the Permian took place mainly in shallow-water tropical areas under oligotrophic conditions. High carbon isotope ratios in Capitanian carbonate rocks (+4 to +6‰ VPDB) mark the ‘Kamura event’ characterized by temporary cooling, high productivity and burial rate. Evaporites in the central part of the Karst Dinarides and red beds of the ‘Gröden type’ indicate a warm and mostly arid climate. Calculations based on the oxygen isotopic compositions of whole-rock carbonate and fossil samples estimate latest Permian temperatures up to 26 °C.

Influence of terrestrial sedimentation in Pennsylvanian rocks of Croatia

Sedimentary rocks of Pennsylvanian age outcrop at several regions in Croatia. Most of these rocks were deposited in a marine environment, in different tectonic units: Karst (External) Dinarides, Internal Dinarides and Tisia. Pennsylvanian deposits contain a significant amount of terrestrial debris, related to the uplift of the Hercynian mountain belt and its intense erosion. Remnants of land flora are not common, but are present at almost all localities. The most diverse and the best preserved Pennsylvanian land flora in Croatia was discovered on the Velebit Mt. and in the Lika Region. It was dominated by ferns, pteridosperms and cordaitales. The fossil flora from Banovina is less diverse, with pteridosperms, scarce ferns, horsetails and lycopods. The sporadic occurrence of lycopods and horsetails was reported from the mountains of NW Croatia. In the Gorski Kotar Region only plant detritus was observed. Ferns and pteridosperms from Papuk Mt. were discovered in older, Mississippian deposits. Palaeobotanical data reopen the discussion about the palaeogeographic position of the research areas.

Sequential Indicator Simulations maps of porosity, depth and thickness of Miocene clastic sediments in the Kloštar field, Northern Croatia

Data from selected Lower Pontian sandstone reservoir in the Kloštar Field, situated in the Sava Depression (Northern Croatia), were used for mapping with Sequential Indicator Simulations rather than using a classical approach. Such approaches offer better insight in distribution of geological variables or zonal uncertainties in the cases with larger datasets (15 points or more). Obtained maps of porosity and reservoir thickness are presented here along with probability maps of certain selected cut of values of petrophysical parameters. Maps showed distinct sedimentological features that can clearly be observed on the both sets of maps.

The Benkovac Stone Member of the Promina Formation: A Late Eocene Succession of Storm-Dominated Shelf Deposits

The Upper Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. This unit occurs in the middle part of the Promina Formation, which is a spectacular calciclastic succession of deposits of late Middle Eocene to Early Oligocene age, about 2000 m thick, showing an upward trasition from deep-marine turbidites to shallow-marine and alluvial deposits. The sheet-like sandstone beds of the Benkovac Stone Member are mainly 1–25 cm thick and have been classified into 6 facies and 3 subfacies, differing in stratification or showing various internal sequences of stratification types. The thicker and most common beds show plane-parallel stratification passing upward into hummocky cross-lamination and undulatory to flat parallel lamination (Facies S1), or consist of only the latter two divisions (Facies S2). Subordinate beds show convolute stratification (Facies S3), are amalgamated (Facies S4), or are homogenized and merely graded (Facies S6). The thinner beds have more uneven boundaries and show translatory ripple cross-lamination (Subfacies S5a), climbing ripple cross-lamination (Subfacies S5b) or pinch-and-swell lamination attributed to starved and rolling-grain ripples (Subfacies S5c). The intervening mudstone beds (Facies M) are silt-streaked and bioturbated. Trace fossils indicate a combination of Zoophycos and Cruziana ichnofacies. The sedimentary succession was deposited in a microtidal offshore transition zone characterized by muddy “background” sedimentation punctuated by discrete storm events. The observed spectrum of tempestite sandstone beds represents a wide range of storm events, varying in magnitude and in the mode of sand dispersal – from the pure action of oscillatory waves to pure geostrophic currents. The majority of tempestites are attributed to a combination of these two end-member factors, with the geostrophic currents often enhanced by a high load of sediment suspension (density-modified currents). The Benkovac Stone Member is underlain by muddy offshore deposits (Debelo Brdo Member) and covered by sandy to gravelly shoreface deposits (Otavac Member), which in turn pass upwards into braidplain deltaic and alluvial deposits. This regressive succession is considered to be a parasequence deposited as a highstand systems tract during a gradual, stepwise rise of relative sea level. The thick parasequence consists of progradational and retrogradational sets of much smaller parasequences, the record of which differs markedly in the shoreface and offshore transitional part. The difference is attributed to the underlying contrast in the physical factors controlling the supply of sand to these shallow shelf zones.

Upper Palaeozoic Fossils from Clastic Sedimentary Rocks in the Gorski Kotar Region

Clastic sedimentary rocks in the vicinity of Mrzle Vodice in the Gorski kotar region contain numerous Upper Palaeozoic fossils, preserved as skeletal detritus in calcilithites or within lithoclasts in coarse-grained sediments. Seventy-two taxa have been determined (most of them for the first lime) in this region. The moSt abundant groups are foraminifers and calcareous algae. Calcisponges, echinoderms and bryozoans occur frequently. while remnants of molluscs, brachiopods and ostracods are scarce. The determined taxa range from the Lower Carboniferous (Visean), through the Upper Carboniferous (Moscovian, Kasimovian, Gzhelian), up to the Lower Permian (Asselian) in age. Some of the clastic sediments show traces of the multiple redeposition.