Gamma-ray parameters are widely used to screen organic-rich intervals, yet the influence of lithofacies heterogeneity on the reliability of gamma-ray-based TOC predictions remains incompletely evaluated. This study aims to (1) assess the relationships between gamma-ray parameters and TOC, (2) evaluate how lithofacies heterogeneity influences predictive reliability, and (3) establish practical screening criteria for identifying organic-rich intervals in two Middle Miocene marine successions from the Croatian part of the Pannonian Basin System. Outcrop gamma-ray spectrometry measurements (K, U, Th) and dose rate (DR) were paired with co-located laboratory TOC analyses (Voćin n = 45; Podsused n = 96). Pearson correlation, multiple and simple linear regression, logistic regression for TOC ≥ 1 wt.%, and threshold analysis were applied to evaluate relationships between gamma-ray parameters and organic matter enrichment. U and DR show moderate positive relationships with TOC in both sections, whereas K and Th are not statistically significant predictors. Regression and threshold analyses identify U as the primary predictor of TOC and show more stable and systematic predictive behaviour in the homogeneous Podsused succession than in the heterogeneous Voćin section. The results indicate that lithofacies heterogeneity primarily influences predictive stability rather than the existence of TOC–gamma-ray relationships. The study demonstrates that lithofacies heterogeneity is an important factor influencing the reliability of gamma-ray-based TOC screening and provides a framework for assessing the suitability of uranium and dose-rate proxies in different sedimentary settings.
Pejić et al. (Mon,) studied this question.