The Alps as the main source of sand for the Late Miocene Lake Pannon (Pannonian Basin, Croatia)

The provenance of the Upper Miocene sandstones from the Sava and Drava depressions of the North Croatian Basin was investigated using petrographic, geochemical, and heavy mineral analyses, including Raman spectroscopy. The study of these sandstones, which represent important oil and gas reservoirs in Croatia, allowed reconstruction of the Late Miocene source-to-sink model of the Lake Pannon drainage system and the evolution of the southwestern Pannonian Basin. The studied feldspatho-litho-quartzose sandstones consist of a mixture of sedimentary, metamorphic, and igneous detritus. Heavy-mineral assemblages are dominated by almandine-rich garnet with apatite, epidote, tourmaline, rutile, zircon, staurolite, and zoisite, indicative of low to medium-grade metamorphic source rocks. Higher concentrations of Ca and Mg than in the Upper Continental Crust standard (UCC) additionally reflect the abundance of limestone and dolostone rock fragments as well as carbonate cement. Geochemical compositional variations between sandstone samples from the Sava and Drava depressions primarily stem from diagenetic processes. CIX and alpha values indicate only minor weathering. Compositional features indicate an orogenic source located in the Eastern Alps and primarily represented by Austroalpine and Penninic nappes. This research offers a novel perspective to distinguish the Upper Miocene reservoirs from other sedimentary units within the basin, contributing to a more comprehensive understanding of the regional geological dynamics and supporting future exploration projects also related to energy transition.