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Evolution of Medvednica Mt.from the Late Miocene to the Pleistocene: The role of sediment source

Medvednica Mt. is situated in the south-western part of the Pannonian basin system (PBS) ; a depositional area located between the mountain chains of the Alps, the Carpathians and the Dinarides. During the Middle Miocene the Pannonian basin existed as a part of the marine Central Paratethys, in the Late Miocene it was covered by the brackish Lake Pannon, while during post-Miocene time it was a mainland dissected by a branched river network, floodplains and small freshwater lakes (KOVAČIĆ, 2004 ; PILLER et al., 2007). The PBS consists of several deep basins separated by uplifted blocks. The thickness of the Upper Miocene, the Pliocene and the Quaternary deposits in the deep basins in the SW part of the PBS exceeds 5000 m, while on the uplifted blocks it is less than 1000 m (SAFTIĆ et al., 2003). The Medvednica Mt. represents an uplifted block which separates the Zagorje basin in the NW from the Sava basin in the SE. Due to tectonic activities from the Middle Miocene to the Quaternary (TOMLJENOVIĆ & CSONTOS, 2001), and lake level oscillations during the Late Miocene, Medvednica Mt. had a changing role as a source of clastic material. At the beginning of the Late Miocene some parts of Medvednica were above the lake water level and acted as a source of clastic material. The material disconformably covered Middle Miocene or/and older rocks, but more often it was transported to the lake and deposited together with shallow–water limestones or deep–water marls. During the middle Late Miocene, as a consequence of a water level rise in Lake Pannon, Medvednica was completely flooded and ceased to exist as a source of clastic detritus. Until the end of the Miocene it formed an underwater hill that separated the Zagorje basin from the Sava basin. The next depositional phase started on the northern slopes of Medvednica at the end of the deposition of Banatica beds, while on the southern slopes it started during the deposition of Abichi beds. Mineralogically and structurally mature sandy to silty material derived from the Alps by prograding deltaic systems was supplied to Lake Pannon causing its shallowing and narrowing. The deposition began in a prodelta environment which was, by the end of the Miocene, gradually replaced by a delta front environment. During the Early Pliocene Medvednica was covered by floodplains with an extensive river network, small lakes and swamps. The clastic material still originated from the Alps (KOVAČIĆ, 2004). The new compressional phase in the evolution of the PBS which started at the end of the Miocene and intensified in the Quaternary (TOMLJENOVIĆ & CSONTOS, 2001) caused strong uplifting of Medvednica. During the Pleistocene Medvednica was a mountain and again became an important source producing a huge amount of clastic material.

Medvednica Mt.; Late Miocene; Pleistocene; clastic material; provenance

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