To reconstruct the Triassic–Jurassic geodynamic evolution through time and space and to distinguish the various lithologies, a high-resolution litho- and biostratigraphy is the necessary base. In cases various lithologies are defined as basin-wide useable formations, in other cases several formations are united into a group, because the included formations are characterized by facies transitions, mixed lithologies, or are not mappable lithostratigraphic units. To invent for identical lithostratigraphic units in different countries/areas independent formations with definition of a separate type-section confuse only readers, hamper the scientific progress, and result often in regional insufficient interpretations which cannot be easily compared with the over-regional tectonostratigraphic evolution, i.e. the geodynamic evolution of the birth and death of an oceanic realm (Wilson cycle). In the Neo-Tethys Wilson cycle the carbonate dominated passive continental margin evolution started in the Middle Triassic (Pelsonian) and ended in the Middle Jurassic with obduction of Neo-Tethys derived ophiolites. During this evolution carbonate platforms were formed predominantly in the Late Triassic (Wetterstein and Dachstein Carbonate platforms). For passive continental margin settings, an intraplatform basin is defined as a deep-water depositional realm situated between two carbonate platforms with lively carbonate production. A basin between the continental realm, i.e. the shore line and a platform (or rising reef-rims) is defined as deep lagoon or empty bucket. After the demise of the Middle Anisian shallow-water carbonate ramp and the formation of a horst-and-graben morphology no significant long-lasting shallow-water carbonate production can be recognized. This change was termed Reifling turnover, and can be traced throughout the whole Western Tethys Realm. The late Middle Anisian to Early Carnian deep-water sedimentary rocks cannot be attributed as “intraplatform basin”, because during this time span no huge carbonate platforms existed. In the latest Ladinian respectively in the Early Carnian the first important carbonate platform cycle started with the evolution of the Wetterstein Carbonate platforms established predominantly on top of preexisting morphological highs and started from there to prograde rapidly towards the basins (grabens/halfgrabens) formed during the Late Anisian extension. Carbonate production of the Wetterstein Carbonate Platform evolution stopped abruptly around the Julian 1/2 boundary and not all preexisting deep-water areas could be filled by the carbonates of this platform. During the short time span of several independent Wetterstein Carbonate platforms also short-living intraplatform basins could be recognized. Carbonate production recovered during the Late Carnian and gave rise for the evolution of the huge Norian-Rhaetian Hauptdolomite/Dachstein Carbonate Platform. The enormous carbonate production of this platform was able to fill all remaining older depressions in the shelf area already in the Early Norian. After the demise of the Dachstein Carbonate Platform during the Triassic/Jurassic mass extinction a hemipelagic shelf evolved (Early-Middle Jurassic). The Middle-Late Jurassic is characterized by ophiolite obduction and the formation of various mélanges and nappe thrusting. Trench-like basins were formed in front of the newly formed nappe stack, and by the erosional products predominantly of the imbricated outer shelf (Triassic deep-water limestones). In cases deep-water Hallstatt nappes were bulldozed by the obducting ophiolites to the foreland.
How to cite: Gawlick, H.-J.: Triassic intraplatform basins versus Middle-Late Jurassic mélanges and nappes in the Western Tethys Realm: Renaissance of Mojsiscovics? or “What is written in the sedimentary successions?”, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-11, https://doi.org/10.5194/egusphere-alpshop2026-11, 2026.
Stratigraphic changes in size and shape of calcareous microplankton near the Tithonian–Berriasian boundary are a key indicator of paleoenvironmental changes in Tethyan realm. Changes in calpionellid size occurred in parallel with a significant increase in the calcareous nannoplankton abundance. This process is associated with the shift of the carbonate production maximum from shallow shelves to the open ocean. These calpionellid “blooms” are not an isolated phenomenon, but part of a broader restructuring of ocean ecosystems. Although the so-called “Calpionella alpina bloom event” (characterized by high abundance of the small spherical forms) has been known for a long time, its exact dynamics and relationship to biostratigraphic boundaries have not yet been quantitatively processed at high stratigraphic resolution.
The aim of this study was to verify, through high-resolution calpionellid morphometry, whether this bioevent is a one-time event or a recurrent process, and to determine its exact position relative to biostratigraphic markers, especially relative to the latest occurrences of the genus Crassicollaria.
The samples were obtained from the pelagic carbonate succession at Brodno (Pieniny Klippen Belt, Western Carpathians). We measured the loricae length (Ll) and width (Wl) in thin-sections using light microscopy. Out of a total of 15,081 individuals; 7,833 were analysed after filtering (exclusion of oblique sections). Advanced statistical methods were used to identify trends: “punctuation” models characterized by intervals of stasis that are separated by sudden jumps, SiZer analysis (for stability of trends in size or shape at different stratigraphic resolutions) and principal coordinate analyses (PCO) assessing variability in increment-specific size and shape distributions.
Our analysis revealed three separate minima in lorica size. The first minimum (the base of the Remanei Subzone) was not accompanied by changes in shape (Ll ~50 µm). The second minimum is located near the Intermedia/Colomi Subzone (Ll ~60 µm). This minimum corresponds to the first Calpionella alpina bloom interval, which precedes the lower boundary of the Calpionella Zone as detected by Michalík et al. (2009, 2021). The third minimum occurs in the lowermost part of Alpina Subzone (the second Calpionella alpina bloom interval), which is characterized by small and spherical calpionellid forms. These three minima of size reduction are clearly separated by periods of larger individuals (Ll ~80 µm). The synchronous response of the genera Calpionella and Crassicollaria to these changes suggests that the entire community was responding to the same oceanographic triggers, probably changes in temperature or nutrient availability.
Our study demonstrated that a quantitative approach allows for a finer biostratigraphic subdivision and a better interpretation of the evolutionary dynamics of microplankton. The synchronized response of different groups of microplankton to environmental disturbances (e.g. warming) is often manifested by a body size decrease. In future, we propose to combine these morphometric data with calcareous nannofossils, calcareous dinoflagellate cysts high-resolution analysis and geochemical proxy data (Mg/Ca), which could clarify whether the observed calpionellid size minima are linked to specific phases of nannoplankton expansion and changes in the global carbon cycle.
This study was supported by the Slovak Research and Development Agency (APVV 22/0523).
How to cite: Ölveczká, D. and Tomašových, A.: Title: High-resolution calpionellid morphometry: A new perspective on the dynamics and timing of bioevents at the Tithonian–Berriasian boundary, 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-30, https://doi.org/10.5194/egusphere-alpshop2026-30, 2026.
Chaotic deposits represent ubiquitous features of the Alps and, in general, of convergent margin settings; consequently, their accurate interpretation is a prerequisite for reconstructing the subduction dynamics and basin evolution characteristic of the Alps and their analogues.
The study deal with the chaotic deposits of the Cretaceous-Eocene Western Ligurian (Helminthoid) Flysch of the Ligurian Alps. We focused on the Eocene part of the Flysch succession, deposited between the Briançonnais-Prepiemontese margin and the advancing orogenic wedge. In particular we provide new mapping and stratigraphic analysis of two formations, i.e., the Colla Domenica Shales and the overlying Leverone Formation, which are exposed between the Prepiemontese and Piemontese-Ligure oceanic domains. The Colla Domenica Shales consist of fine-grained sediments embedding polygenic chaotic layers, stratigraphically overlain by the turbiditic deposits of the Leverone Formation. Traditionally interpreted as Cretaceous trench sediments influenced by mud diapirism, these successions are here reassessed through a comprehensive multidisciplinary approach—integrating field mapping, sedimentology, biostratigraphy, petrography, and geochemistry—to better define the tectonostratigraphic history of this Alpine segment.
New data indicate that these chaotic intervals are Paleocene–Eocene Mass Transport Deposits (MTDs), emplaced during the final stages of oceanic closure.
Key diagnostic features, including matrix-supported fabrics, erosional basal contacts, and disordered clast distribution, point toward high-energy gravity-driven processes triggered by slope instability at the front of a prograding accretionary prism. Geochemical signatures from basalt clasts (Transitional-MORB) suggest that products of early oceanic magmatism were first incorporated into the prism and subsequently remobilized during mass-failure events. All the evidence supports a polygenetic origin of the mélanges, characterized by a main sedimentary nature due to MTDs interlayered with turbiditic deposits, partially overprinted by subsequent tectonic activity. Provenance analyses on siliciclastic sandstones document a source area located within the European margin, likely corresponding to the Corsica block. An upward increase in sandstone immaturity indicates a progressively shorter transport distance of the sediments which can be explained by a closing basin. Indeed, the last depocenters of the Piedmont-Ligurian basin were characterized by two source areas located at the European margin (siliciclastic turbiditic sediments) on one side and the accretionary prism (ophiolite-bearing MTDs) on the other side. New findings contribute to understanding the origin and significance of chaotic deposits in collisional settings, improving our knowledge of depocenter migration, sediment-routing pathways, and accretionary prism dynamics during the closure of the Piemontese-Ligure Ocean.
How to cite: Lombardi, S., Lorenzo, S., Pierre, M., Mattia, B., Miriam, C., Laura, F., Laura, C., Silvio, S., and Matteo, M.: Origin and evolution of the Paleocene-Eocene chaotic facies from the Western Ligurian Flysch (Ligurian Alps, Italy), 17th EGU Émile Argand Conference on Alpine Geological Studies, Fruška Gora, Serbia, 14–16 Sep 2026, alpshop2026-26, https://doi.org/10.5194/egusphere-alpshop2026-26, 2026.
