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Paleoecology and Paleoenvironment of the Upper Karpatian-Lower Bedenian Sedimentary Succession from SE Medvednica Mt., Croatia

The Miocene sediments of the Northern Croatia belongs to the SW margin of the Central Paratethys (Pannonian Basin System). Beside the Lower Badenian sediments of the Plaz locality near village Čučerje (SE Medvednica Mt.) described previously by AVANIĆ et al. (1995) and ĆORIĆ et al. (2009), approximately 50 m thick Upper Karpatian to Lower Badenian underlying succession along the Bokanjščica stream has been also studied. Upper Karpatian (Bokanjščica stream): The lowermost part of marine sedimentary succession consists mostly of fossiliferous calcareous mudrocks (marls) deposited on the deeper shelf and in the offshore-transition zone, below the fair-weather wave base. According to calcareous nannoplankton, Helicolith horizon (NN4 Zone) have been determined. The last appearance datum (LAD) of Helicosphaera ampliamperta is noticed in sample where Sphenolithus heteromorphus Paracme ends that represents a very useful correlation tool defining the Subzone MNN4b. Planktonic foraminiferal assemblage consists of numerous specimens of the cool surface water indicators such as Tenuitella angustiumbilicata and Globigerinita glutinata. Frequent occurrence of infaunal benthic foraminifera such as Bulimina, Bolivina and Nonion indicate low oxygen but organic carbon reach sea bottom. Lower Badenian (Bokanjščica stream): The middle part of marine sedimentary succession consists of fossiliferous calcareous mudrock deposited on the deeper shelf environment. On the basis of calcareous nannoplankton Lower Badenian Helicosphaera waltrans horizon (NN5 Zone) is determined. The regular occurrence of Sphenolithus heteromorphus, together with close records of Helicosphaera waltrans upwards, corresponds to the Mediterranean Subzone MNN5a. Sediments contain reach and highly diversified calcareous benthic foraminiferal assemblage dominated by infaunal organic carbon-preferring genera such as Bulimina, and low-oxygen adapted taxa like Bolivina, Uvigerina and Pappina indicating middle shelf environment. First occurrence of the shallow and warm-water preferring genera like Elphidium, Glabratella and Pararotalia have also been detected. Planktonic foraminiferal association is characterized by cool water taxa (Tenuitella spp., Turborotalita quinqueloba ; 10%) and also by abundant presence of surface warm-water species Cassigerinella chipolensis (50%). The Lower Badenian ostracod fauna is dominated by deep marine species (Cytherella compressa, Cytherella aff. vandenboldi, Henryhowella asperrima, Parakrithe dactylomorpha, Krithe sp., Krithe cf. monosteracensis, Cardobairdia sp. and Argilloecia acuminate). A few valves of the shallow-water species (Costa edwardsi, Loxocorniculum cf. hastatum, Loxoconcha sp., Grinioneis haidingeri) are also present. Discovery of very rare Indo-Pacific species Paijenborchella iocosa indicates the establishment of connections between the Paratethys Sea, Mediterranean realm and Indo- Pacific Ocean. Palynological analyses show relatively abundant dinocyst association (Systematophora placacantha, Melitasphaeridium choanophorum). All these facts indicate sedimentation in marine somewhat deeper and distal environment. Lower Badenian (Plaz section): The upper part of the Plaz section predominantly consists of calcareous mudrocks which are intercalated with layers of sandstones. The upper part of the profile is predominantly composed of sandstones and to a lesser extent of calcareous mudrocks, with tuffs on the top. It is a coarsening- upward succession indicating shallowing of the marine environment. Sediments contain shallow and warm water preferring benthic foraminifera (Elphidium, Asterigerinata, Ammonia and Amphistegina), whereas planktonic foraminifera are absent or very rare. Echinoderms, bryozoans and molluscan carbonate shell fragments are also present. Palynofacies is composed of diverse association of spores, pollen grains, foraminiferal test linings, dinocysts and fragments of colonial green alga Botryococcus braunii and dinocysts (Operculodinium centrocarpum, Hystrichosphaeropsis obscura, Hystrichokolpoma rigaudiae, Melitasphaeridium choanophorum) which indicate Badenian age and sedimentation in marine but somewhat shallower and more proximal environment in reach of terrestrial input. The upper Karpathian sediments of the investigated secctions correspond to the Mi2 cooling event that induced climate instability and larger temperature oscilations. During Early Badenian warmer climate and MMCO was reestablished, but with more fluctuating environment.

Upper Karpatian‒Lower Badenian ; Biostratigraphy ; Lithology ; Paleoecology ; Paleoenvironment

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