Mts. Kalnik and Požeška gora volcaniclastic sequences hold valuable information concerning the Miocene syn-rift evolution of the North Croatian Basin, and the evolution of the Carpathian-Pannonian Region and the Central Paratethys. We present volcanological, high-precision geochronological, and compositional data of volcanic glass to constrain their tephrochronology, magmatic provenance, and timing of the initial Central Paratethys flooding of the North Croatian Basin. Based on CA-ID-TIMS U-Pb zircon ages (18.060 ± 0.023 Ma for Mt. Kalnik and 15.345 ± 0.020 Ma for Mt. Požeška gora) and coeval 40 Ar/ 39 Ar sanidine ages (18.14 ± 0.38 Ma and 18.25 ± 0.38 Ma for Mt. Kalnik and 15.34 ± 0.32 Ma and 15.43 ± 0.32 Ma for Mt. Požeška gora), Mt. Kalnik rhyolitic massive ignimbrites and Mt. Požeška gora rhyolitic primary volcaniclastic turbidites are coeval with Carpathian-Pannonian Region Miocene post-collisional silicic volcanism, which was caused by lithospheric thinning of the Pannonian Basin. Their affiliation to Carpathian-Pannonian Region magmatic activity is supported by their subduction-related geochemical signatures. Although Mts. Kalnik and Požeška gora volcaniclastics are coeval with the Bükkalja Volcanic Field Csv-2 rhyolitic ignimbrites, North Alpine Foreland Basin, Styrian Basin, Vienna Basin, and Dinaride Lake System bentonites and volcaniclastic deposits, reliable tephrochronological interpretations based on comparison of volcanic glass geochemical composition are not possible due to a lack of data and/or methodological discrepancies. Our new high-precision geochronology data prove that the initial Middle Miocene (Badenian) marine flooding of parts of the North Croatian Basin occurred at least ~ 0.35 Ma (during the NN4 Zone) before the generally accepted ~ 15 Ma maximum flooding age at the basin scale, calibrating the timing of the onset of the widespread "mid-Langhian" Central Paratethys flooding.
Abstract: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.
The Miocene deposits of the Hrvatska Kostajnica (KOS-I) area belong to the south-western marginal part of the Pannonian Basin System (PBS). Investigation of the lithostratigraphical column included: mineralogical, geochemical, sedimentological and integrated palaeontological (calcareous nannofossil, foraminifers, ostracodes, palynomorphs) analyses. Badenian and Sarmatian sediments of this column were deposited in a marine offshore environment with local input of terrigenous material represented by marls and silty marls. Based on palaeontological data, the recorded palaeoclimate was subtropical in the late Badenian changing to a warm temperate climate of the early Sarmatian. Marly sediments predominantly consist of carbonate (calcite and aragonite) and clay minerals, while quartz and plagioclase are less abundant. Most samples contain a small amount of zeolite minerals from the clinoptilolite/heulandite series. Among the clay minerals, smectite and illite/muscovite are the most abundant. Based on provenance analyses we concluded that the Badenian-Sarmatian marls were predominantly formed by the weathering of acidic (Si-rich) source rock derived material from the neighbouring Inner Dinarides.
Upper Miocene to Pliocene (Pannonian) sediments of the Pannonian Basin System accumulated in the brackish Lake Pannon and the fluvial feeder systems, between 11.6-2.6 Ma. Their stratigraphic subdivision has been problematic for a long time due to the laterally prograding architecture of the basin fill and the historically independently evolving stratigraphic schemes of the neighbouring countries. We correlated the lithostratigraphic units of the Lake Pannon deposits between Hungary and Croatia in the Drava Basin, using lithological, sedimentological and palaeontological data from boreholes and outcrops, and seismic correlation. The Croatica and Medvedski breg formations in Croatia correspond to the Endrőd Fm. in Hungary, comprising shallow to deep water, open lacustrine, calcareous to argillaceous marls. The Andraševec fm. in Croatia corresponds to the Szolnok and Algyő Fms. in Hungary, consisting of sandstones and siltstones of turbidite systems and of clay marls deposited on the shelf-break slope. The Nova Gradiška fm. in Croatia is an equivalent of the Újfalu Fm. in Hungary, built up of a variety of lithologies, including sand, silt, clay and huminitic clay, deposited in deltaic environments. The Pluska fm. in Croatia corresponds to the Zagyva Fm. in Hungary, consisting of variegated clays, silts, sands and lignites, deposited in alluvial and fluvial environments. Coarse-grained (sand, gravel) basal layers are assigned to the Kálla and Békés Fms. and the Sveti Matej member of the Croatica fm. Coarse-grained intercalations within the deep-water marls belong to the Dorozsma Member of the Endrőd Fm. in Hungary, and to the Bačun member of the Medvedski breg fm. in Croatia. Sediment transport and lateral accretion of the shelf edge in the Drava Basin took place from the N, NW, and W, to the S, SE, and E, respectively. According to the biostratigraphic and chronostratigraphic analyses, the oldest shelf-break slopes in the Mura Basin are more than 8 Ma old, whereas the youngest ones in the southeasternmost part of the Drava Basin may be Pliocene in age (younger than 5.3 Ma). Thus, the 180 km long and at least 700 m deep Drava Basin was transformed into a fluvial plain during the last 3.5 million years of the Miocene.
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