Indications of Provenance and Source Rock Contributions in Paleogene Deposits from Zrinska Gora, Croatia

A significant portion of Zrinska Gora mountain in Croatia is covered by Paleogene siliciclastic deposits. These deposits are thought to have formed in a flexural foreland basin that developed during the Late Cretaceous and Paleogene along the northwestern segment of the Sava Zone, a tectonic unit formed by the continental collision of the Adria plate and the Tisza Mega-Unit (Ustaszewski et al., 2010).

This study investigates the sedimentological and petrological characteristics of Paleogene sedimentary deposits, focusing on conglomerates, to reconstruct their provenance and depositional history. Our methodology included sedimentological logging and sampling, optical microscopy and heavy mineral analysis. Detailed petrographic investigation of conglomerate pebbles resulted in the determination of 12 lithotypes, comprising various magmatic, volcaniclastic, cataclastic, and metamorphic rock types, based on their mineralogical and structural-textural characteristics. Associated sandstones classify as litharenites with phyllosilicate and hematite cement, containing rock fragments similar to the lithologies observed in the conglomerate pebbles.

Provenance analysis suggests that the clastic material primarily originated from units of the Sava Zone, as indicated by granophyre, syenite, and monzonite clasts. Volcanic pebbles point to mixed sources from various Mesozoic complexes, while metamorphic clasts reflect contributions from pre-Eocene formations across the broader area, exhibiting medium- to high-grade regional metamorphism. Notably, a slight shift in heavy mineral composition across the studied localities suggests a relocation of the primary sediment source, possibly from the Western Vardar Ophiolitic Unit to the Sava Zone and Tisza Mega-Unit, reflecting tectonically driven sedimentary reorganization in the foreland basin. These findings provide new and preliminary insights into the development of clastic sediments in syncollisional basins along the northwestern part of the Sava Zone during the Paleogene. The presented work is supported by the Croatian Science Foundation project SECret (HRZZ IPS-2023-02-2683).

 

References:

Ustaszewski, K., Kounov, A., Schmid, S.M., Schaltegger, Fügenschuh, B. et al. (2010): Evolution of the Adria‐Europe plate boundary in the northern Dinarides: From continent‐continent collision to back‐arc extension. Tectonics, 29(6), 34.