Search

The North Croatian Basin (NCB) evolved during the Miocene as a part of the SW margin of the Pannonian Basin (Carpathian-Pannonian Region, CPR). A major transgressive-regressive sedimentary cycle in the NCB is represented by an initial deposition in alluvial and lacustrine environments, followed by Central Paratethyan marine environments, and a subsequent return to lacustrine and alluvial depositional environments (Pavelić & Kovačić, 2018). Indications for these variable depositional conditions that are linked to the marine flooding of the NCB are preserved in sediments on Mt. Medvednica (Pavelić and Kovačić, 2018 ; Avanić, 1997). Due to the intensive and long-lasting CPR magmatic activity, numerous referent volcaniclastic layers are preserved in stratigraphically and environmentally different sedimentary facies. We applied an integrated stratigraphic, compositional and geochronological approach on the three volcaniclastic horizons (ČUČ-1, ČUČ-6, PL) intercalated within the marine sediments on Mt. Medvednica to determine the flooding history and the timing of the initial Miocene Central Paratethys transgression of the western part of NCB, as well as to enable the correlation of the volcaniclastic layers. Volcaniclastic deposits ČUČ-1 and ČUČ-6 are fine to coarse tuffs intercalated with massive marls. The sequence of calcarenite, tuff, and calcisiltites recorded at site PL indicate a gradual deepening of the marine environment. The composition of volcaniclastic samples from all three sites is similar, with dominantly > 50% vitric juvenile particles (pumice and volcanic shards) with subordinate magmatic minerals (feldspar, biotite, quartz, and amphiboles). The samples are well preserved, with rarely visible volcanic glass alteration. Rhyolitic glass compositions (>77% wt. SiO2 ; ranging from rhyolites to high-K rhyolites) from all 3 volcaniclastic horizons suggest an origin from major silicic eruptive events of the CPR. Future trace element measurements of glass shards will provide additional constraints to distinguish primary from secondary volcaniclastics. New high-precision CA-ID-TIMS U-Pb zircon dates indicate that the ČUČ-1 volcaniclastic horizon (up to 15.44 Ma) is older than the PL horizon (14.937 ± 0.012 Ma), as suggested by Avanić (1997). Since ČUČ-1 zircon dates range from 15.44 and 15.9 Ma, it is not possible to interpret a high-precision age, however, the absence of zircons younger than ~15.44 Ma implies the existence of NCB marine deposits older than ~14.8 Ma (Marković, 2017 ; PL this study). This data is also indicating that the initial Middle Miocene Central Paratethys flooding of the western (Mt. Medvednica) and the eastern (Mt. Požeška gora, Brlek et al. 2020) parts of the NCB occurred earlier than the previously accepted ~15 Ma maximum flooding age. References: Avanić, R. (1997): Analiza facijesa srednjeg miocena jugoistočnog dijela Medvednice, Master Thesis, University of Zagreb. Brlek, M. et al. (2020): Miocene syn-rift evolution of the North Croatian Basin (Carpathian-Pannonian Region): new constraints from Mts. Kalnik and Požeška gora volcaniclastic record with regional implications. International Journal of Earth Sciences 109:2775–2800. Marković, F. (2017): Miocene tuffs of the North Croatian Basin, Dissertation, University of Zagreb. Pavelić, D., Kovačić, M. (2018): Sedimentology and stratigraphy of the Neogene rift-type North Croatian Basin (Pannonian Basin System, Croatia): a review. Mar Pet Geol 91:455–469.

The formation and evolution of the Pannonian Basin as part of the Carpathian-Pannonian Region (CPR) was accompanied by voluminous silicic eruptions during Early and Middle Miocene [1]. Silicic pyroclastic material, which covered much of the CPR, can be found in Miocene deposits in the North Croatian Basin (NCB, SW part of Pannonian Basin). This research is focused on two main outcrops of volcaniclastic rocks on Mts. Kalnik and Požeška Gora. Samples are in a procces of analyses using a ”multi-proxy“ approach, combining sedimentological, petrological and paleontological data, high-precision zircon geo(petro)chronology, 40Ar/39Ar radiometric dating along with geochemistry and isotopic composition of volcanic glass and minerals. First results from Mt. Kalnik volcaniclastic deposits characterized them as massive rhyolitic ignimbrites with a CA-ID-TIMS U-Pb zircon age of 18.06 ± 0.023 Ma [2]. These results indicate that potentially correlative volcaniclastic deposits are intercalated with marine sediments in the Hrvatsko Zagorje Basin and lake sediments in the Sinj Basin. Guided by results from Avanić [3] and de Leeuw [4], we sampled nine additional volcaniclastic outcrops. Furthermore, deposites that might be correlative with Mt. Požeška gora primary volcanoclastic turbidites are found on Mt. Medvednica intercalated in marine sediments of Central Paratethys. New CA-ID-TIMS zircon ages indicates that the initial Middle Miocene marine flooding of the western part of the NCB (Mt. Medvednica) could have occurred contemporaneously with its eastern part (Mt. Požeška Gora, 15.345 ± 0.02 Ma, [2]). Integrated data will enable more reliable tephrochronological and volcanic provenance, as well as petrogenetic reconstructions of Mts. Kalnik and Požeška Gora volcaniclastic deposits. This work is supported by the Croatian Science Foundation through project „Miocene syn-rift evolution of the North Croatian Basin (Carpathian-Pannonian Region): a multi-proxy approach, correlation and integration of sedimentary and volcanic record“ (PYROSKA), (UIP-2019-04-7761).

The Mt. Strahinjščica in NW Croatia contains volcano-sedimentary successions formed along the NE margin of Adria during period of arc-related extension in the Middle-Late Triassic. It is built of sedimentary (dolomitic rocks, radiolarites, cherts, clay, siltstones and sandstones), magmatic rocks (altered andesitic basalts and diabases), and tuffs. The Sekolje section on the southern slope of Strahinjščica Mt. represents a 100-meter thick volcano-sedimentary succession with pyroclastic and siliciclastic lithofacies types. The pyroclastic facies is recorded in the section from the beginning to 38.90 m. It consists of two different lithotypes: vitroclastic and crystaloclastic tuffs. Vitroclastic tuffs are composed of fine ash with glass shards and pumice fragments. Both glass shards and pumice fragments are devitrified into microcrystalline quartz, albite, clay minerals, calcite and chlorite respectively. Rare crystalloclasts of quartz and K-feldspar/plagioclase are still present. Crystalloclastic tuffs are composed of coarse ash to lapilli sized pyroclastic material. Dominant crystalloclasts are quartz, plagioclase and K- feldspars, with less biotite. Quartz crystalloclasts are angular with varied size, show jig-saw fit texture, and occasionally have oval- spherical cavities typical for volatile rich systems. Plagioclase and K-feldspar crystalloclasts have mainly hypidiomorphic to idiomorphic shape. Carbonate and silicified tuff lithoclasts and chert are subordinate. Matrix of the crystalloclastic tuffs is made of fine ash devitrified to chlorite, microcrystalline quartz, clay minerals, opaque minerals, with carbonate domains sporadically. The siliciclastic facies between 38.90 and 100.60 m is divided into siltstone and volcanogenic sandstone lithotypes. Dark grey to brown siltstones are homogenous, thin bedded or laminated with radiolarian-rich lamina and lenses. Grains of quartz, K-feldspar and muscovite are recognized in the siltstones, while the matrix is composed of chlorite, clay minerals, sericite, and organic matter. Volcanogenic sandstones are poorly sorted and composed mainly of pyroclastic and volcanogenic particles, with approximately equal amount of highly altered feldspars and lithoclasts, and some quartz grains. Matrix is composed of chlorite, sericite, fine quartz and feldspar grains. Described lithofacies types at Sekolje section suggest that the sedimentation of the pyroclastic material occurred simultaneously with active volcanism. Occurrence of two lithotypes in the pyroclastic facies indicate segregation of the material from the bulk pyroclastic cloud through sedimentation processes. Crystalloclastic coarse pyroclasts were transported and deposited by gravity currents, while fine ash tuffs, consisting mainly of glass shards, settled from suspensions. These processes could have happened after the pyroclastic eruption and syn-eruptive resedimentation to the deeper marine environment while the siliciclastic facies was deposited during abating volcanic activity. Siltstones were deposited in distal, probably anoxic environments. The organic matter in this lithofacies consists of charcoalified plant debrís, palynomorphs are extremely rare. The coarsening of clastic material in the upper part of the section and transition to the volcanogenic sandstones can be interpreted as shallowing of the basin areas and/or increased proximity to the source area.

The Transylvanian Basin located in the eastern segment of the Pannonian Basin System (PBS) provides an ex-cellent insight into the early evolution of Lake Pannon. Lower Pannonian deep- water deposits, which are often buried deep in the Hungarian and Croatian part of the PBS are exposed on the surface. Despite the stratigraphic significance and rich fauna, a systematic palaeontological and biostratigraphic evaluation, including palynology, has not been carried out yet. The detailed multiproxy analysis (palaeontology including palynology, magnetostratigraphy and authigenic 10Be/9Be dating) of the Guşteriţa section fills a significant gap in the chronostratigraphic assessment of the Pannonian stage in Transylvania.The Guşteriţa clay pit near Sibiu exposes a continu-ous deep-water lower Pannonian section. The outcrop en- compasses a 55 m thick section of grey laminated or mas-sive marl and silty marl layers with fine-very fine-grained cross- laminated sand intercalations. The section hosts a rich fossil assemblage, including molluscs, ostracods, thecamoe-bians, fish teeth, otoliths, some partial fish skeletons, and fossil plants.Besides molluscs typical for Congeria banatica beds, organic-walled microplankton assemblages with dinocysts in particular, represent a powerful tool for biostratigraphic subdivision within the PBS. After the connection to the Eastern Paratethys and the Mediterranean region ceased around 11.6 Ma ago, Lake Pannon was formed in the Cen-tral Paratethys area. The brackish-water conditions initiated a remarkable radiation among organic- walled dinoflagel-lates. The isolated evolution of these dinocysts resulted in rapid morphological changes, which formed the basis of several regional biozonation schemes developed for the Hungarian and Croatian part of the PBS (e.g., SÜTŐ-SZ-ENTAI, 2000 ; BAKRAČ et al., 2012).A total of 25 palynological samples have been collected from the uppermost 25 metres of the quarry. The samples reveal a moderately diverse, but excellently preserved di-nocyst assemblage and several other aquatic (acritarchs & green algae) and terrestrial palynomorph groups (spore & pollen). The majority of the dinocysts are endemic Panno- nian taxa, e.g. Spiniferites pannonicus, Spiniferites oblongus, and various species of the genus Virgodinium, Impagidini- um, and Pontiadinium. The Guşteriţa dinocyst assemblages resemble those of Spiniferites bentorii oblongus biozone and the Pontiadinium pecsvaradensis biozone from the Hungarian part of the PBS. The biostratigraphic correlation sug-gests an age range between 11.0 and 10.6 Ma. This age assignment agrees with the magnetostratigraphy that placed the section into the C5n.2n long normal polarity mag-netic chron (11.056-9.984 Ma, ATNTS2012). Similarly, the calculated age from authigenic 10Be/9Be isotopic dating provided an age of 10.84 ± 0.4 Ma.The large amount of terrestrial palynomorphs and re-worked older Miocene taxa (e.g., Polysphaeridiumzoharyi, Cleistosphaeridiumplacacanthum and Melitasphaeridiumsp.) indicates intense erosion and runoff into the lake from the adjacent hinterland. Abundant bisaccate conifer pollen and Tsuga (hemlock) represent extrazonal vegetation elements originating pro- bably from the emerging mountains around the lake. Car-ya (hickory) and Tilia (linden) are characteristic elements of a warm-temperate mesophytic broad- leaved deciduous forests, while the high abundance of Taxodiaceae pollen indicates the presence of swamps along the shore. The new data also reveal the palaeogeographical con- nections between the Transylvanian Basin and other areas of the PBS which ceased by ca. 9 Ma ago. The integration of the new biostratigraphic subdivision with magnetostra- tigraphy and authigenic 10Be/9Be isotopic dating represent a significant improvement of the regional Pannonian chron-ostratigraphy and its correlation to the global time scale.

Microscopic plant remains (spores and pollen) allow us to trace vegetation and detect environmental, especially climatic changes from deep time in the geological past. The Late Triassic (237-201 Ma) period is marked by an array of environmental changes such as large scale volcanism, a meteorite impact and global climate change. This study describes the response of vegetation from two periods of the Late Triassic, the Carnian (237-227 Ma) and Norian (227-209 Ma), from three locations: the UK, Hungary and SW USA.

In the Triassic, the depositional area of the TR was located on the western shelf of the Tethys between the Northern Calcareous Alps, Drauzug and the Southern Alpine realms. The Late Triassic marine succession of the Transdanubian Range (TR) Hungary shows a significant change in sedimentation during the Carnian. The pelagic carbonate deposition was replaced by a short-termed interval with the formation of marly sediments of the Veszprém Marl Formation (VMF). The VMF was deposited in two transgressive-regressive cycles, each cycle referring to a member (Mencshely and Csicsó Marl Members) with the VMF. The VMF hosts diverse and well-persevered palynological assemblages. Besides a few pioneer studies with only few sampled horizon, detailed palynological studies have not been carried out yet. Our new palynological and palynofacies data contribute to the biostratigraphic subdivision and palaeoenvironmental interpretation of the Veszprém Marl Formation. A total of 63 samples from two boreholes: Mencshely (MET-1) and Veszprém (V-1) were processed for palynological analysis. Both quantitative and qualitative analyses have been performed. The identified taxa correspond to typical Carnian morphospecies in Europe e.g., Camerosporites secatus, Duplicisporites spp., Partitisporites spp., Enzonalasporites vigens, Patinapsorites densus, Vallasporites ignacii, ., Alisporites spp., Infernopollenites spp., Lueckisporites singhii, Lunatisporites acutus, Ovalipollis ovalis, Staurosaccites quadrifidus, Aulisporites astigmosus including various spores e.g., Aratrisporites spp., Paraconcavisporites lunzensis, Converrucosisporites sp. and Verrucosisporites moruluae. Based on the quantitative palynological study three assemblages are recognized. The oldest assemblage (acutus-vigens-singhii) in the lower part of the Mencshely Marl Member is characterized by the predominance of E. vigens, L. acutus, L. singhii with many Circumpolles species. Lueckisporites singhii is far less common in the second assemblage (vigens-acutus). The youngest assemblage (astigmosus-densus) is marked by the common occurrence of Aulisporties astigmosus, Patinasporites densus, Partitisporites maljawkinae and various Aratrisporites species in the uppermost few metres of the Mencshely Marl Member and in the overlaying Csicsó Marl Member. The correlation to ammonite biozontion suggests that the whole studied succession is late Julian (Julian 2, austriacum Zone). The palynological assemblages and stratigraphic range of selected taxa enables the correlation to other alpine Triassic areas and the NW European Germanic Basin. The palynofacies indicates strong terrestrial influx in a marine setting inferred from the common presence of acritarchs, foraminiferal tests linings and scarce occurrence of dinocysts. The terrestrial input increases in the Csicsó Marl Member. The changes in spore-pollen assemblages can be linked to climatic variations and can be regarded as the manifestation of the Carnian Pluvial Episode.

The geological record contains evidence for numerous pronounced perturbations in the global carbon cycle, some of which are associated with mass extinction. In the Carnian (Late Triassic), evidence from sedimentology and fossil pollen points to a significant change in climate, resulting in biotic turnover, during a time termed the ‘Carnian Pluvial Episode’ (CPE). Evidence from the marine realm suggests a causal relationship between the CPE, a global ‘wet’ period, and the injection of light carbon into the atmosphere. Here we provide the first evidence from a terrestrial stratigraphic succession of at least five significant negative C-isotope excursions (CIE)’s through the CPE recorded in both bulk organic carbon and compound specific plant leaf waxes. Furthermore, construction of a floating astronomical timescale for 1.09 Ma of the Late Triassic, based on the recognition of 405 ka eccentricity cycles in elemental abundance and gamma ray (GR) data, allows for the estimation of a duration for the isotope excursion(s). Source mixing calculations reveal that the observed substantial shift(s) in δ13C was most likely caused by a combination of volcanic emissions, subsequent warming and the dissociation of methane clathrates.

Correlation of the palynological assemblages from the low latitude Chinle Formation in North America and the high latitude or Tethyan assemblages in Europe is difficult, because of vegetation provincialism as a result of climatic heterogeneity. This significant offset between the European and American palynofloras is the result of the generally hot and semi-arid climate in the eastern part of Pangea and the western Tethyan realm and a more humid tropical belt in lower latitudes. The Norian is characterized by dolomite formation in the Alpine realm and playa lake deposits in the northwest European realm. However, in lower latitudes in western Pangea, fluvial environments supported rich riparian vegetation due to the seasonally wet climate until the middle Norian. The differences in climate resulted in a significant offset between the stratigraphic ranges of some European Carnian/Norian index taxa. In some cases the parent plants of some typically Carnian taxa from Europe thrived longer in the American southwest. Due to this offset, the Chinle Formation in North America was thought to encompass the Carnian and Norian stages based on palynostratigraphy, but palaeomagnetic correlations and recent radiometric dating suggested middle to late Norian age. We documented the first time the occurrence of the pollen Perinopollenites elatoides from the middle part of the Chinle Formation (Sonsela Member) that represents the only evidence so far from the pollen record that indicates the Norian age of the Chinle Formation and is in agreement with magnetostratigraphy and radiometric dating. This species also provides the first correlation possibility to European coeval palynofloras. Moreover, new palynological data suggest that approximately simultaneously with a vertebrate turnover event, a floral turnover occurred in the middle segment of the Chinle Formation around 215 Ma. As a consequence of the new age assignment, the floral and faunal turnover could be constrained to a horizon that may coincide with the Manicougan impact event dated as 215 Ma. This biotic event may also correlate with a significant climate shift towards more arid climate due to the northward shift of the North American continent, and probable pCO2 perturbations from volcanism related to Pangean rifting and the uplift of the Cordilleran Arc. Besides the vegetation change and the rapid diversity loss, the floral turnover around 215 Ma was associated with an increase in opportunistic plant types (e.g., Majonicaceae, Voltziaceae) and an increase in mutant aberrant pollen morphotypes. A similar event without the aberrant pollen types could be distinguished in a younger horizon of the Chinle dated as 211 Ma old. The separation of these two events was only possible based on the precise radiometric dating. In contrast to representing one event, the two events point out the possibility of multiple biotic turnovers that are most likely controlled by cyclic environmental perturbation such as climatic oscillations. However, the aberrant pollen morphotypes are confined to the event around 215 Ma and they might represent the effect of the environmental stress associated with the Manicougan impact event.

The Yanchang Formation was deposited during the Middle Triassic in a vast lacustrine basin in the modern Ordos Basin and is a main target for hydrocarbon exploration in Central China. It is divided, based on sedimentary cycles and lithology, into the Chang 10 (the oldest) to Chang 1 (the youngest) members. During the deposition of the Chang 7 Member, the Ordos lake system reached its maximum depth and large volumes of organic-rich sediments were deposited. The evolution of the Ordos Basin sedimentary system during this phase is, however, not completely understood, and uncertainty still exists as for the chronostratigraphy of Chang 7 Member. We acquired palynological markers and palynofacies and a high-resolution δ13Corg record through the entire Chang 7 Member, and a ID-TIMS 206Pb/238U date of 240.95 ± 0.033 Ma from a volcanic ash bed in the middle of this Member. These imply that the maximum deepening phase of the lacustrine system was during the earliest Ladinian. Evidence of marine influence in the Ordos Basin at that time and comparison to the sea-level oscillations observed in Western Tethys suggest that a global eustatic rise and highstand may have played a role in determining lake-level variations.