Spectral Gamma-Ray Variability Within Carbonate Lithofacies: An Example from the Early Triassic Lower Mahil Formation (Upper Khuff-Equivalent) of Al Jabal Al-Akhdar, North Oman: An Example from the Early Triassic Lower Mahil Formation (Upper Khuff-Equivalent) of Al Jabal Al-Akhdar, North Oman

This study aims to test the relationship between the elements Potassium (K), Uranium (U), and Thorium (Th) measured by spectral gamma-ray to sedimentary facies. Spectral gamma-ray is widely used in depositional facies and sequence stratigraphic analysis. Here, spectral gamma-ray U, Th, and K measurements from two logged sections of the Early Triassic Lower Mahil Formation (Upper Khuff-equivalent, KS1) of Al Jabal Al-Akhdar (Saiq Plateau and Wadi Sahtan), north Oman, are discussed. A detailed sedimentological description for both logged sections was performed using Dunham’s classification, and spectral gamma-ray measurements were taken every 10 cm with an RS-230 BGO Handheld Spectrometer. Several lithofacies were identified, including breccia, packstone/grainstone, and mudstone. Saiq Plateau and Wadi Sahtan lithofacies are grain-dominated facies (e.g., shoals), which indicate that the Lower Mahil Formation was deposited in a shallow carbonate ramp (shoal to foreshoal setting). In all lithofacies in the Lower Mahil Member, the percentage of U exceeds Th and K. This relative enrichment of the U reflects the reduction conditions and high preservation of organic matter.