Thermal maturity of Carboniferous to Eocene Sediments of the Alpine-Dinaric Transition Zone (Slovenia)

The Alpine-Dinaric Transition Zone in Slovenia comprises the fold and thrust belt of the Southern Alps (South Karawanken Range, Julian Alps), Slovenian Basin and the Dinarides. The Slovenian Basin located between the Julian and Dinaric carbonate platforms evolved during Middle Triassic time and remained in a deep marine setting till the Late Cretaceous. The thermal history of Carboniferous to Eocene rocks in that area was investigated using vitrinite reflectance (VR) data, apatite fission track analysis and numeric 1D basin modeling. The study shows that maturity patterns are mainly controlled by the thickness of Upper Cretaceous to Eocene flysch deposits, filling the accommodation space. Therefore the thermal overprint reaches a maximum (> 4%Rr) in Triassic to Cretaceous sediments of the Slovenian Basin and decreases towards the north and south. Minor sedimentary burial of the Adriatic Carbonate Platform and the Julian Alps results in a lower thermal overprint (< 1.5%Rr). The thickness of flysch sediments was about 5 km in the area of the Sava Folds, but significantly higher in the central part of the Slovenian Basin. Heat flow during maximum burial in Eocene time was in the order of the global average (60 mW/m2). Cooling of Paleozoic and Mesozoic sediments below 110 °C occurred between Late Eocene and Early Oligocene times in different parts of the study area. Nappe stacking due to Early (Dinaric) and Late Cenozoic (Alpine) compressional tectonics did not influence the thermal maturity of the sediments.