The Internal Western Carpathians comprise a complex Alpine thin-skinned nappe system derived from the Meliata domain. In its lowermost structural position, the Meliata Unit (Meliaticum) represents a remnant of the Neo-Tethyan oceanic suture and includes the blueschist-facies Bôrka Nappe, low-grade syn-orogenic accretionary complexes of the Meliata Unit s.s., and chaotic ophiolite-bearing mélanges. In this study, we focus on deep-sea sediments from the Meliata Unit and on comparable units of similar age and structural position within the Internal Western Carpathians, particularly the Turnaicum and Silicicum. Our dataset consists mainly of radiolarites in association with shales and claystone. Although the samples can be broadly divided into Triassic and Jurassic age groups, their geochemical composition reveals information that goes beyond biostratigraphic age constraints. As pelagic sediments deposited far from major continental input, radiolarites preserve signatures of seawater chemistry, hydrothermal activity, and detrital supply. These records allow us to reconstruct depositional conditions, sediment provenance, and the tectonic evolution of the Meliata oceanic domain. All 31 samples processed by whole-rock analysis were recalculated to eliminate the carbonate component and loss on ignition. The results show pronounced variability in the processes affecting the Meliata oceanic domain through time and space. In the Al₂O₃/(Al₂O₃ + Fe₂O₃) versus Fe₂O₃/TiO₂ discrimination diagram after Murray (1994), most samples define a trend from continental margin to ocean ridge affinity. Provenance discrimination for shales after Roser and Korsch (1988) indicates mature continental sedimentary sources. PAAS-normalized REE patterns further distinguish lithological groups. Shales display higher total REE concentrations and flatter profiles, whereas radiolarites are characterized by lower REE abundances and significantly more variable patterns. Several samples show a clear negative Ce anomaly, suggesting oxidizing marine conditions or seawater influence during sedimentation. A weak positive Eu anomaly in some samples may reflect a minor terrigenous contribution. These geochemical signatures demonstrate that radiolarites and associated shales from the Internal Western Carpathians record both local depositional conditions and broader tectonic evolution of the Meliata oceanic domain. Together, they provide a geochemical framework for tracing the transition from continental-margin sedimentation to more oceanic settings. This approach highlights the value of pelagic sediments as archives of ancient basin evolution and plate-boundary processes. Additional analyses of radiolarite and siliciclastic pelagic sediment samples from other tectonic units and paleoprovenances, together with comparisons to well-characterized geological settings, are necessary to fully and reliably interpret the obtained geochemical data.
Acknowledgements: The research was supported by projects of the Slovak Research and Development Agency (APVV-21-0281; SK-SRB-25-0031), Grant Agency for Science, Slovakia (VEGA 1/0021/25) and National Science Centre, Poland (2021/43/B/ST10/02312).
Murray R.W., 1994. Chemical criteria to identify the depositional environment of chert: general principles and applications. Sedimentary Geology, 90: 213-232.
Roser B.P. and Korsch R.J., 1988. Provenance signatures of sandstone-mudstone suites determined using discrimination function analysis of major-element data. Chem Geol, 67: 119-139.
How to cite: Molčan Matejová, M., Potočný, T., and Plašienka, D.: More Than Just Age: Geochemical signatures of radiolarites from the Internal Western Carpathians, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-78, https://doi.org/10.5194/egusphere-alpshop2026-78, 2026.
The Jurassic–Early Cretaceous successions of the Danubian Unit in the Carpatho-Balkanides, studied in three structurally superposed sections in the Danube River valley (Djerić et al. 2026), record the evolution of the southern passive margin of the Alpine Atlantic domain. Integrated sedimentological, biostratigraphic and chemostratigraphic constraints document an evolutionary progression from Early-to-early Middle Jurassic syn-rift extension and subsidence, through Bajocian–Oxfordian tectonic quiescence, to the Late Oxfordian–Kimmeridgian onset of a Štramberk-type carbonate platform. The Lower Jurassic–Bajocian interval records a continental to shallow-marine transgression linked to early rifting of the easternmost Alpine Atlantic domain. Continental break-up and syn-rift differential subsidence led to the establishment of a horst-and-graben system marked by condensed Rosso Ammonitico deposition on structural highs and accumulation of thick radiolaritic basinal successions. Bajocian–Oxfordian tectonic quiescence was followed by the Late Oxfordian–Kimmeridgian development of Štramberk-type carbonate platforms that prograded basinward until the early Late Tithonian. Calcareous turbidites reached proximal basinal settings during the Late Oxfordian, whereas distal areas remained carbonate-starved until the Tithonian, when episodic platform-derived mass-transport deposits were transported into the basin. During the Berriasian–Valanginian, Biancone-type hemipelagic limestones blanketed the entire region, reflecting the stabilization of outer-shelf to basinal conditions across the former horst-and-graben topography.
Regional correlation with coeval successions in Romania (Southern Carpathians), Tisza, the Western Carpathians, the Southern and Eastern Alps, and the Apennines demonstrates the coherence of the Danubian Unit as part of the southern Alpine Atlantic passive margin, refining existing Mesozoic palaeogeographic interpretations of the Alpine–Carpathian realm.
Reference
Djerić N., Jach R., Goričan Š., Reháková D., Uchman A., Gawlick H.-J., Schlögl J. & Stojadinović U. 2026. Jurassic – Early Cretaceous depositional history of the Alpine Atlantic southern passive margin: Inferences from the Serbian Carpathians. Global and Planetary Change, 259: 105372. https://doi.org/10.1016/j.gloplacha.2026.105372.
How to cite: Djeric, N., Jach, R., Goričan, Š., Reháková, D., Uchman, A., Gawlick, H.-J., Schlögl, J., and Stojadinovic, U.: Biostratigraphy, chemostratigraphy, and facies evolution of the easternmost Alpine Atlantic realm (Southern Carpathians, eastern Serbia), 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-13, https://doi.org/10.5194/egusphere-alpshop2026-13, 2026.
The Dinarides are largely built of Mesozoic deposits derived from the Adriatic microplate and ophiolites originating from the Neotethys Ocean. While the External Dinarides are predominantly composed of shallow-marine carbonates deposited on the Adriatic Carbonate Platform (AdCP), the Internal Dinarides, together with the ophiolites, preserve remnants of the deeply submerged eastern Adriatic continental margin. Radiolarian research in the Dinarides has largely focused on pelagic sediments associated with ophiolites, whereas continental-margin successions remain poorly explored. This contrasts with the Southern Alps, where the preserved pelagic domains of the Adriatic margin became classical localities for Mesozoic radiolarian research.
The oldest radiolarian-bearing deposits attributed to the Adriatic margin in the Dinarides originated in Middle Triassic rift basins associated with the opening of the Neotethys. This pelagic episode is recorded in both the External and Internal Dinarides. Late Anisian and Early Ladinian radiolarian assemblages from these basins, comparable to those found atop the oldest Neotethyan oceanic crust, are generally diverse and well preserved, reflecting deposition in nutrient-rich, oxygenated environments. A low-diversity assemblage from a restricted intraplatform basin has also been reported from the External Dinarides. Pelagic conditions in the smaller of these basins ceased during the Ladinian, although seafloor spreading in the Neotethys continued throughout the Late Triassic.
Following Middle Triassic rifting, the eastern Adriatic margin was characterised by a horst-and-graben architecture comprising several basins and topographic highs aligned parallel to the Neotethyan mid-ocean ridge. This architecture is best preserved in the central and southern Dinarides. There, the Durmitor High separated the Bosnian Basin from the Lim Basin, which was in turn separated from the deep-water environment of the distal continental margin by the Drina–Ivanjica High. The Bosnian Basin, which occupied the proximal part on the margin relative to the AdCP, extended northwards, with correlative successions now exposed in the northern Dinarides and the Southern Alps. Here, however, there is no evidence of the large-scale horst-and-graben topography.
During the Late Triassic and Early Jurassic, regarded as the period of seafloor spreading in the Neotethys, carbonate sedimentation prevailed in the pelagic basins of the eastern Adriatic margin, and no radiolarian assemblages of this age have been reported. During the Middle Jurassic, sedimentation shifted from carbonate to siliceous, reflecting a regional change in ocean-surface fertility. At the same time, tectonic conditions within the Neotethys changed from extension to convergence. In the Lim Basin, a late Aalenian radiolarian assemblage has been reported from a shale-dominated interval, whereas Middle and Late Jurassic assemblages have been described from cherts in all pelagic domains of the eastern Adriatic margin.
In the latest Jurassic, with the rapid diversification of oligotrophic nannoplankton, pelagic limestones began to accumulate above radiolarites in the basins of the western Tethyan realm. This transition has also been recorded in the basins of the eastern Adriatic margin; however, radiolarian assemblages of this age have been reported only from the Southern Alps. Simultaneously, syn-orogenic deposits began to accumulate in the pelagic basins of the eastern Adriatic margin, documenting the onset of ophiolite obduction.
How to cite: Kukoč, D., Goričan, Š., Vukovski, M., Smirčić, D., and Slovenec, D.: Mesozoic evolution of the eastern Adriatic continental margin preserved in the Internal Dinarides – a radiolarian perspective, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-67, https://doi.org/10.5194/egusphere-alpshop2026-67, 2026.
The Lesser Caucasus represents a key component of the Alpine-Himalayan mountain belt, as it preserves the remnants of a Tethyan oceanic realm that continues westwards into northeastern Turkey. Their spatial continuation to the south-southeast, into Iranian territory, still remains poorly understood. Radiolarian data obtained during the last twenty years have been particulalry useful for the establishment of an accurate chronostratigraphic framework for the depositional and geodynamic history of the Tethyan realm in this region. We here present recently obtained radiolarian age data from northern and eastern Armenia that enrich the existing dataset by dating radiolarites most of which are in stratigraphic contact with submarine lavas. In the Bazoum region of northern Armenia, in a very tectonized and chaotic state, radiolarites and submarine lavas crop out in the Sevguet valley, which are part of the Stepanavan-Amasia sector of the Amasia-Sevan-Hakari (or Sevan-Akera) ophiolite zone considered a suture. A large lense of radiolarian cherts incorporated in submarine lavas (basaltic trachyandesite, ‘Within-plate’ affinity) yielded a late Bajocian – early Bathonian radiolarian assemblage that can be correlated with the zones 5-6 of Baumgartner et al. (1995). East of the Sevan lake, in the Daranak locality, submarine basaltic flows that correspond to basanites (OIB-type, alkaline affinity ; Galoyan et al. 2009) are intercalated by radiolarites that are now dated as late Oxfordian/early Kimmerdidgian to late Kimmeridgian/early Tithonian in age (zones 10-11 of Baumgartner et al. 1995).
References
Baumgartner P.O., Bartolini A., Carter E.S., Conti M., Cortese G., Danelian T., De Wever P., Dumitrica P., Dumitrica-Jud R., Gorican S., Guex J., Hull D.M., Kito N., Marcucci M., Matsuoka A., Murchey B., O’Dogherty L., Savary J., Vishnevskaya V., Widz D. and Yao A., 1995. Middle Jurassic to Early Cretaceous Radiolarian biochronology of Tethys based on Unitary Associations. In: Baumgartner et al. (Eds.), Middle Jurassic to Lower Cretaceous Radiolaria of Tethys: Occurrences, Systematics, Biochronology. Mém. Géol. (Lausanne), 23: 1013-1048.
Galoyan G., Rolland Y., Sosson M., Corsini M., Billo S., Verati C. and Melkonian R., 2009. Geology, geochemistry and 40Ar/39Ar dating of Sevan ophiolites (lesser Caucasus, Armenia): evidence for Jurassic back-arc opening and hot spot event between the south Armenian block and Eurasia. J. Asian Earth Sci., 34: 135-153.
How to cite: Danelian, T., Turakiewicz, V., Galoyan, G., and Seyler, M.: Jurassic and Cretaceous radiolarian age constraints for the Mesozoic evolution of the Tethyan realm in the Lesser Caucasus ; new data from Armenia, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-29, https://doi.org/10.5194/egusphere-alpshop2026-29, 2026.
In setting up the Global Boundary Stratotype and Section (GSSP) for the Jurassic–Cretaceous boundary (JKB), the Berriasian Working Group (BWG) of the International Subcommission on Cretaceous Stratigraphy recommends to shift down the JKB to an interval between the paleomaginetic M20n1r and the base of M19r. The BWG is discussing markers defining the JKB. Radiolarians are one of ideal candidates for defining the JKB because they are wide spread and can be found in both shallow and deep marine sedimentary facies worldwide. The JKB lies around the base of the Unitary Association Zone (UAZ) 13 and within the Pseudodictyomitra carpatica Zone. Our radiolarian biostratigraphic research around the JKB in two Itarian sections, Torre de’Busi (Lombardian Basin) and Bosso Valley (central Apennines), and at ODP Site 801 in the western Pacific enables to correlate these sections by means of radiolarians.
The Torre de’Busi and Bosso Valley sections are strong GSSP candidates in the Alpine Tethys. The Maiolica Formation, which includes the JKB at the lowermost part, is characterized by whitish beige to gray colored, well-bedded micritic limestones with abundant black to gray chert layers and nodules. Integrated calcareous nannofossil, calpionellid, magnetostratigraphic, and cyclostratigraphic investigations provide a reliable stratigraphic framework for the Torre de’Busi section. Calpionellid biostratigaraphic and magnetostratigraphic study was conducted in the Bosso Valley section. A total of 49 samples in the Torre de’Busi section and 47 samples in the Bosso Valley section have been collected for our radiolarian biostratigraphic study across the JKB. In the Torre de’Busi section only horizons corresponding to the lower part of M20 contain moderately preserved radiolarians. In the Bosso Valley section several horizons corresponding to the interval between the M20n1r and the base of M19r yielded moderately to well preserved radiolarians.
Radiolarian biostratigraphy accross the JKB in the western Pacific was studied at ODP Site 801. The Pseudodictyomitra carpatica Zone is recognized in a radiolarite sequence from Core 15 to Core 20 at the site. Radiolarian markers for delimimating the JKB can be selected among taxa of which first occurrence is recorded in the UAZ 13. The result of a radiolarian biostratigraphic correlation between Alpine Tethys sections and western Pacific sections is presented. Candidates of radiolarian markers for the JKB are discussed. They are included in the genera Cinguloturris, Hemicryptocapsa, Hsuum, Loopus, Pantanellium, Vallupus, and Zhamoidellum.
How to cite: Matsuoka, A., Li, X., Bertinelli, A., and Chiari, M.: Radiolarian biostratigraphic correlation around the Jurassic–Cretaceous boundary between the Alpine Tethys and the Pacific, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-45, https://doi.org/10.5194/egusphere-alpshop2026-45, 2026.
Unlike other system boundaries, the Jurassic-Cretaceous transition (J-K) is gradual, without a mass extinction event accompanied by major excursions of stable isotope curves. Significantly, continuous sedimentation of radiolarian-rich siliceous sediments occurred during the transition throughout the Neotethys (NT) and Panthalassa, which represented >80% of the J-K world ocean.
We studied radiolarian assemblages across the J-K in two distant areas: 1.) The Central Atlantic and Western Tethys and 2.) The Argo Abyssal Plain (AAP., ODP Site 765, off NW-Australia. J-K paleolatitude 45° S). Both areas share a similar geodynamic context of Pangaea breakup creating young ocean basins during the Middle-Late Jurassic. The studied sections reveal different radiolarian faunal evolutions but both respond to major palaeoceanographic and paleoclimatic changes across the J-K.
1.) In Western Tethys the change from radiolarite to pelagic cherty limestone is interpreted as the result of cooler, dryer climates during the Tithonian-Berriasian Dry Event. Less continental weathering, hence, less nutrient input created more oligotrophic surface waters resulting in a major radiolarian turnover in the NT-realm. UAZ13 (Baumgartner et al. 1995), straddling the J-K, is defined by 39 FO's at its base and 9 LO's at its top. Oligotrophic conditions also triggered the rise and explosion of calcareous nannoplankton and calpionellids. UAZ 13 correlates with the Crassicollaria Zone, the FO’s of hyaline calpionellids, and Nannoconus.
2.) In the AAP the first Tethyan radiolarians appear in Core 61 containing the J-K. Ranges of typical Tethyan species such as Podocapsa amphitreptera or Acaeniotyle umbilicata begin earlier in NT. Their later appearance in the AAP is the result of its opening towards NT. Tethyan taxa are rare before the Valanginian/Hauterivian and become common by the Aptian-Albian.
Several latest Jurassic-Early Cretaceous lineages of Austral Radiolaria (Nodosphaera, Praewindalia, Windalia, Archaeotanella, Morchella, Fusitanella, Argofusus, Baumgartner et al. 2023) are recorded in the AAP cores, but were also observed in S-Patagonia, Antarctic Peninsula, Wedell Sea (ODP Site 69), Kolbano Mega Sequence of Rote and Timor, originally deposited on the NW-Australian margin, and in Southern Tibet, interpreted as the NT distal continental margin of Greater India. The rapid evolution of Austral Radiolaria is the biotic response to the development during J-K of a an early circum-S-polar current system.
Radiolarian biogeography and plate tectonic models support a scenario of palaeoceanographic and global climatic change during the J-K related to progressive Pangea break-up with 3 consequences: 1). Increased heat transfer to the Southern hemisphere causing cooling of NT regions during the J-K Dry Event. 2.) Northward shift of the southern summer ITCZ reducing the NT monsoon area and establishment of a southern NT subtropical gyre. 3.) The south-polar West Wind Drift forced a circum-Antarctic-Australian cold current through the epicontinental rift between India and Antarctica since the J-K, transporting Austral Radiolaria into the AAP.
Baumgartner, P.O. et al. (Eds.). 1995. Middle Jurassic to Lower Cretaceous Radiolaria of Tethys. Mém. de Géol. Lausanne 23.
Baumgartner, P., Li, X., Matsuoka, A., Vérard, C. 2023. Austral and Subtropical Gyre Radiolaria – latest Jurassic to Early Cretaceous Leg 123, Site 765, Argo Abyssal Plain revisited. Micropaleontology. 69. 555-633. 10.47894/mpal.69.6.01.
How to cite: Baumgartner, P. O., Li, X., Atsushi, M., Luis, O., and Špela, G.: Radiolarian response to the Jurassic-Cretaceous transition: Pangea breakup and the end of the Tethyan mega-monsoon, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-48, https://doi.org/10.5194/egusphere-alpshop2026-48, 2026.
