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Petrography and provenance of Early Miocene conglomerates from Medvednica Mt. (Pannonian Basin, Croatia)

The Early Miocene conglomerates represent the oldest sediments deposited in the southwestern part of the Pannonian Basin (PB). One of the most representative outcrops of these conglomerates is located on the southeastern flanks of Medvednica Mt. where they are deposited in alluvial environment transgressively on Paleozoic-Mesozoic basement (ŠIKIĆ, 1995). The aim of this research is to determine composition and provenance of these conglomerates. The conglomerates have been determined as weakly lithified clast-supported petromict conglomerate. The pebbles average size is 3 to 7 cm reaching 30 cm. Size of pebbles diminish, while pebble sorting increase with distance from the contact with basement. Microscopic analyses of pebbles show that sandstones prevail, while limestones (packstone, grainstone, rudstone and mudstone), siltites, metamorphic rocks (marble, quartzite, metasiltite, metasandstone) and several types of granites are subordinate. Within sandstone pebbles carbonate sandstone (calclitites, calcarenites and calcarenaceous sandstones) prevails over arcose, subarcose and lithic arenites. The composition of pebbles and their size suggest that the source area was very heterogeneous and located in near hinterland. Great resemblance of pebble composition with surface exposure of Paleozoic-Mesozoic of Mt. Medvednica core rocks point to conclusion that these rock were the best candidate for the source rocks. Nevertheless, granite from the conglomerate pebbles differs from the granites from the only known Medvednica Mt. locality (MAJER & MAJER, 1974) implying that the granite pebbles originate from rocks which are no longer represented on the surface of the Mt. Medvednica. Also, the orientation of imbricated pebbles in similar conglomerates from a outcrop 3 km to the southwest, deposited at the same time, suggests transport of material from the southwest (PAVELIĆ, 1998). Transport of material from the south has also been confirmed for the oldest Miocene conglomerates in the East Croatia i.e. southern part of PB (KOVAČIĆ et al., 2011). That open possibility that the original source rocks of investigated conglomerates were not the rocks from today's core of Mt. Medvednica, but the rocks from source area were located more southerly.

Pannonian Basin; Petrography; Provenance; Early Miocene; Conglomerates

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