ABSTRACTThe strata encompassing the Permian–Triassic boundary interval capture a pivotal period in Earth's history, with significant changes in Phanerozoic Earth system dynamics, culminating in a severe mass extinction. In carbonate platforms, this boundary is marked by a shift from skeletal to microbial carbonate production. Whereas extensive research has focused on the End‐Permian Mass Extinction in open‐marine shelf environments, the transition within inner platform facies remains underexplored due to limited dating options and pervasive dolomitization. This study examines the Permian–Triassic boundary interval at the continuous dolostone, Brušane‐Sy section, in the External Dinarides (Croatia), that retains much of its original fabric. High‐resolution petrography, biostratigraphy and chemostratigraphy (δ13Ccarb and δ13Corg) were utilized to detail sedimentary responses across the boundary. The Upper Permian fine‐crystalline dolostone features well‐preserved cryptomicrobial/bioclastic, peritidal microfacies with calcareous algae and foraminifera. In contrast, the Lower Triassic dolostone, shows a transition to a medium‐crystalline, fabric‐destructive dolostone texture. The transition from fabric‐retentive Permian to fabric‐destructive Triassic dolostone is attributed to two dolomitization processes: (i) Late Permian transgression facilitating aragonite/high Mg‐calcite deposition, later transforming neomorphically into fabric‐retentive dolostone texture due to abundant precursor dolomite nuclei; and (ii) dispersed Early Triassic primary dolomite precipitation later stabilized during shallow burial with decaying microbial mats serving as loci for crystal growth but decreased nucleation. This shift is recorded by a minimal negative δ13Ccarb excursion (≤0.7‰) and a more pronounced shift in Δ13C (δ13Ccarb – δ13Corg; ca 4.6‰). Contrasting with typical open‐marine Permian–Triassic boundary excursions, such isotopic features reflect the localized shift in primary production to photoautotrophy (algae and cyanobacteria) and early dolomitization in the presence of seawater‐derived dissolved inorganic carbon. Understanding these sedimentary and diagenetic dynamics provides crucial insights into environmental changes and biogeochemical cycles affecting Permian–Triassic boundary dolomitization, offering a comprehensive view of the End‐Permian Mass Extinction across a wider range of shallow marine carbonate dominated depositional environments.

Dark-grey cherty limestone from Mt. Svilaja contains moderately well-preserved radiolarians of unusually low diversity. Nineteen genera were encountered, namely, only one fourth of genera known from the time equivalent Buchenstein Formation. Based on conodonts, the studied interval is assigned to the Lower Ladinian Budurovignathus hungaricus Zone. Ammonoids and allochthonous fossil elements (calcareous algae, corals, brachiopods, bivalves, benthic foraminifera, terrestrial-plant remains) from the same interval were previously reported. Facies and organic-matter analyses support the interpretation of depositional setting in a semi-enclosed basin with oxygen-deficient bottom waters. The radiolarian assemblage consists of spherical Entactinaria (Pentactinocarpidae, Heptacladidae, Hindeosphaeridae) and Spumellaria (Archaeocenosphaera, Paurinella, Triassospongosphaera, Spongopallium), and monocyrtid Nassellaria (mostly Hozmadia). Among Pentactinocarpidae, Lobactinocapsa ellipsoconcha Dumitrica is abundant and characterized by considerable variability of the cortical shell regarding its shape (ovoid to spherical), wall thickness (single-layered to spongy), and number of external spines. Eptingiidae, Oertlispongidae, Relindellidae, and all multicyrtid Nassellaria, common in the Buchenstein Formation as well as in radiolarian cherts associated with ophiolites, are missing. Similar, although less drastically reduced radiolarian fauna is known from the coeval San Giorgio Dolomite, which was also deposited in an oxygen-deficient intra-platform basin. The San Giorgio fauna lacks multicyrtid Nassellaria but still contains abundant Eptingiidae, Oertlispongidae, and Relindellidae. The likely factor reducing the diversity in the intra-platform basins was the vertical extent of the oxygen-deficient lower water column. Only surface-dwelling radiolarians were successful in stratified basins with expanded deep-water hypoxia.

Hemipelagic to pelagic (H/P) marls, representing pelitic deposits, accumulated within the foredeep sub-basin of the Dinaric Foreland Basin (northern Neotethyan margin, present-day Croatia) during the Middle to Late Eocene. Syn-sedimentary tectonic movements, paleogeographic position and exchanges of short-lived hyperthermal episodes affected the sedimentation and related mineral and geochemical record of these deposits. Mineral (clay) assemblages bear signature of prevailing physical weathering with significant illite and chlorite content, but climatic seasonality is suggested by smectite-interlayered phases and sporadical increase of kaolinite content. Illite crystallinity varies significantly, and the lowest crystallinity is recorded by the Lutetian samples. Illite chemistry index is always bellow 0.5, being characteristic for Fe-Mg-rich illite. The geochemical records are the most prominent (CIA up to 76, CIW up to 91) for the Istrian Lutetian (42.3–40.5 Ma), but also for Priabonian (35.8–34.3 Ma) samples of Hvar Island. The ICV values (the lowest 1.40 and the highest 10.85) of all studied samples fall above PAAS (ICV = 0.85) and point to their chemical immaturity. The Ga/Rb ratios are lower than 0.2 and K2O/Al2O3 ratios are also low (0.16–0.22), implying transition between cold and dry, and warm and humid climate, obviously trending among several warming episodes.

In the Early to Middle Miocene, the post‐orogenic intramontane lacustrine Sinj Basin that belonged to the Dinarides Lake System evolved in the area of the External Dinarides. A composite 770 m thick stratigraphic column was measured spanning the basin's stratigraphy. Eight facies were differentiated. Four facies are almost entirely composed of freshwater carbonate deposits. Carbonate facies are divided into calcareous mudstone, charophytic micritic limestone, calcisiltite and coquina facies. They are interpreted to belong to a prograding carbonate bench on a gently inclined lake margin. In addition, tuff/clays, carbonate conglomerate, carbonate breccia and coal were differentiated. The tuff/clays are the result of remote volcanic eruptions, while the coarse‐grained sediments belong to subaqueous shallow stream channels or were deposited by gravity flows. The coal at the top of the measured succession, mostly of allochthonous origin, was deposited as a fen forest peat, representing the final stage of the lake. The formation of the Sinj Basin might have been triggered by dissolution of Permo‐Triassic evaporites, within the mostly carbonate basement but also by breakdown and collapse of Mesozoic and Palaeogene carbonate rocks and coalescence of contiguous sinkholes. The non‐tectonic interpretation of the basin genesis is a novel hypothesis explaining the origin of one of the Dinarides intramontane basins and is in contrast to previous considerations that evolution of the Sinj Basin was controlled by strike‐slip or extensional tectonics.

Triassic strata in the Drežnica section, Bosnia and Herzegovina have been examined biostratigraphically. The limestone and dolostone strata were deposited in deep pelagic environment. The conodont faunas are marked by prevailing elements of the genus Pseudofurnishius including clusters that enabled to distinguish the huddlei (lower Longobardian) and murcianus (upper Longobardian–?Cordevolian) Zones, the later fauna is characterized by the presence of Budurovignathus with rare representation of Gladigondolella and Paragondolella. This is the first report on recovery of Pseudofurnishius in the region.

The Teočak section in Bosnia and Herzegovina (Sava-Vardar Zone) composed of the Upper Permian Bellerophon Formation and the Lower Triassic “Werfen Formation” was studied sedimentologically and micropaleontologically by using foraminifers and conodonts. The Bellerophon Formation was deposited in a shallow subtidal lagoon rich in biota characterized by typical Changsingian foraminiferal species. Deposition on a shallow epicontinental ramp with pronounced long-term transgression is proposed for the Lower Triassic strata. The recovered conodont faunas are assigned to the Late Permian praeparvus (Changhsingian) and to the Early Triassic isarcica-staeschei (Griesbachian), costatus (? latest Dienerian-early Smithian) and hungaricus (early Spathian) Zones. The studied strata include the Permian-Triassic Boundary as well as the Induan-Olenekian Boundary. The introduced conodont biozonation in the Teočak section is for the first time proposed for the region and is an important contribution for paleobiogeographic correlation of Western Tethys.

Middle Triassic deposits in the Karst Dinarides (south Lika area, near Gračac) were investigated for petrological, sedimentological and biostratigraphic determinations. Within two continuously recorded sections of sedimentary carbonates and interlayered pyroclastic rocks (Mali Kunovac and Kunovac sections) reflecting variable sedimentary-magmatic environments, valuable cephalopod fauna ranging from the middle Illyrian to the upper Illyrian age was found. The most significant was the recovery of the ammonoids Asseretoceras sp., indicating the upper part of the Illyrian Paraceratites trinodosus Zone, and Reitziites reitzi species which marks the upper part of the Illyrian Reitziites reitzi Zone. The discovery of the Reitziites reitzi species was not known from the Karst Dinarides until this finding.

Conodont ecology of the Early Triassic Smithian-Spathian transition is still poorly understood. Here we use oxygen isotope ratios of monogeneric conodonts from Omani samples to reveal the differences of oxygen isotopic composition between different taxa. Oxygen isotope analyses from Oman reveal that Neogondolella inhabited a deeper part of the water column relative to neospathodids and Icriospathodus. This indicates that species of Neogondolella lived in an environment ca. 1.7 degrees C cooler than where neospathodids lived. The investigation of conodonts from these Smithian and Spathian sections has also enabled the first recovery of some rarely reported species (e.g., Icriospathodus zaksi, Paullella omanensis sp. nov. Chen and Gladigondolella laii sp. nov. Chen) from Oman. Paullella omanensis sp. nov. was further recovered from Plavno, Croatia, indicating a large geographic distribution, and its value for biostratigraphic correlations. The discovery of these species in both Oman and Croatia expands their geographical distribution.

Middle Triassic deposits in the Velebit Mts. of the External Dinarides in Croatia show strong differentiation of sedimentary environments and facies. In the area of Donje PazariSte, a 90 metre thick section includes six different facies, each with its specific genetic characteristics (Flysch-like Facies; Carbonate Shale Facies; Pyroclastic Density Current Facies; Platy Limestone with Pyroclastics Facies; Limestone Breccia Facies and Slumped Limestones with Pyroclastics and Chert Facies). In the same area, in the nearby Top of Donje PazariSte section, a Pyroclastic Flow Facies was defined, and this was also recognized similar to 15 km to south-east, in the area of BruSane Village, in the foothills of Vinac. Throughout the area and section investigated, the effects of intense tectonic and volcanic activity can be traced. The pronounced differences in the facies determined facies are interpreted as consequences of syntectonic and volcanically influenced sedimentation in a graben/half-graben depositional system.

During the earliest Triassic microbial mats flourished in the photic zones of marginal seas, generating widespread microbialites. It has been suggested that anoxic conditions in shallow marine environments, linked to the end-Permian mass extinction, limited mat-inhibiting metazoans allowing for this microbialite expansion. The presence of a diverse suite of proxies indicating oxygenated shallow sea-water conditions (metazoan fossils, biomarkers and redox proxies) from microbialite successions have, however, challenged the inference of anoxic conditions. Here, the distribution and faunal composition of Griesbachian microbialites from China, Iran, Turkey, Armenia, Slovenia and Hungary are investigated to determine the factors that allowed microbialite-forming microbial mats to flourish following the end-Permian crisis. The results presented here show that Neotethyan microbial buildups record a unique faunal association due to the presence of keratose sponges, while the Palaeotethyan buildups have a higher proportion of molluscs and the foraminifera Earlandia. The distribution of the faunal components within the microbial fabrics suggests that, except for the keratose sponges and some microconchids, most of the metazoans were transported into the microbial framework via wave currents. The presence of both microbialites and metazoan associations were limited to oxygenated settings, suggesting that a factor other than anoxia resulted in a relaxation of ecological constraints following the mass extinction event. It is inferred that the end-Permian mass extinction event decreased the diversity and abundance of metazoans to the point of significantly reducing competition, allowing photosynthesis-based microbial mats to flourish in shallow water settings and resulting in the formation of widespread microbialites.

In the central part of the External Dinarides in Plavno, Croatia, near Knin, a remarkably thick (927.5 m) Early Triassic depositional sequence was investigated. The Plavno sequence starts in the EarlyGriesbachian and ends with a continuous transition into the Anisian strata. A complete 13 C isotope curve has been achieved and combined with conodonts, bivalves and ammonoids to establish and correlate stage and substage boundaries. The δ 13 C curve is consistent with former studies. It displays a general increase from the Griesbachian to a prominent maximum beyond the +8‰ amplitude around the Dienerian-Smithian boundary (DSB), followed by a steep and continuous decline to low, negative values in the Smithian. Around the Smithian-Spathian boundary (SSB) a steep rise to a second maximum occurred. It is followed by a saw-tooth shaped decline in the Spathian and a similar increase to a peak at the Spathian-Anisian boundary (SAB). Sedimentologically, the Plavno sequence is interpreted as having been deposited on an extensive epeiric ramp under long-term transgressive conditions, sharing depositional characteristics of both the epeiric platform and the carbonate ramp. The entire Plavno sequence was deposited above the storm-wave base and was storm influenced. Three informal members are differentiated: 1) the dolostone member (Early Griesbachian); 2) the siliciclastic member (red-coloured shale, siltstone, sandstone with oolitic/bioclastic grainstone intercalations), which can be further divided into lower, middle and upper intervals (Late Griesbachian, Dienerian and Smithian); and 3) the mudstone member (grey lime mudstones, marls and calcisiltites with common ammonoids and gastropods-Spathian). The Plavno sequence is compared with other western Tethyan sections. Observed differences stem from local controls on deposition in the overall shallow marine environment.

Upper Permian and lowermost Triassic strata of the Masore section in western Slovenia have been restudied by means of bio- and lithostratigraphy. This section is mainly characterized by a carbonate succession of the Bellerophon Formation deposited in a shallow marine ramp environment that was located in the western part of the Paleotethys. The Permian-Triassic boundary (PTB) transition is marked by laminated microbialites – stromatolites interpreted to reflect a deeper ramp environment. The conodont elements recovered enabled the recognition of the Hindeodus praeparvus Zone of the uppermost Permian (Upper Changhsingian) in the Bellerophon Formation. Gondolellids are documented in the PTB transitional interval with microbial microfacies, whereas the Isarcicella isarcica Zone (Lower Griesbachian, Lower Triassic) is recognized in the tectonically separated Werfen Formation just above the microbial microfacies part of the section. The lowermost part of the microbialites is characterized by Late Permian species of foraminifers indicating that at least this part of the section is still Upper Permian.

Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides: Donje Pazarište, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazarište were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.

Middle Triassic volcaniclastic rocks have been recognized at several localities in the vicinity of Bosansko Grahovo, in the southwestern part of Bosnia and Herzegovina in the External Dinarides. Peculiar types of autoclastic rocks were investigated. These are peperites and hyaloclastites. Regarding specific structures, mineral composition and micropetrographic characteristics hyaloclastites observed at section Bosansko Grahovo I represent genetic succession. It was possible to further differentiate hyaloclastites into a) in situ hyaloclastites, b) slightly resedimented hyaloclastites and c) resedimented hyaloclastites. Genesis of peperites is related to lava emplacement in unconsolidated water saturated pelagic lime mudstones. In situ hyaloclastites and slightly resedimented hyaloclastites were formed due to quenching at the contact of basaltic lava effusions with sea water. Detritus of resedimented hyaloclastites, where volcanic rock fragments are mixed with limestone/chert clasts, imply reworking after fragmentation and redeposition possibly in the vicinity of primary volcanic basalt effusion. All rock types occurred in the deep sea troughs that formed as a consequence of Middle Triassic extensional tectonic and rift related wrench faulting. All investigated rock types represent the first findings of autoclastic deposits in the External Dinarides. Biostratigraphic constraints achieved by means of conodont species Neogondolella excentrica, Paragondolella excelsa, Paragondolella trammeri and Gladigondolella tethydis indicate Late Anisian to Early Ladinian interval of the autoclastic deposits from Bosansko Grahovo.