Sequence Stratigraphy and Chemostratigraphy Interpretations Based on Stable Isotope and Gamma Ray: An Example from the Early Triassic Lower Mahil Formation [Upper Khuff Outcrop Equivalent (KS1)], al Jabal Al-Akhdar, North Oman, Sultanate of Oman: An Example from the Early Triassic Lower Mahil Formation [Upper Khuff Outcrop Equivalent (KS1)], al Jabal Al-Akhdar, North Oman, Sultanate of Oman

This study aims to integrate facies distribution, stable isotope, spectral and total gamma rays to build high-resolution sequence stratigraphy of the Early Triassic Lower Mahil Formation [Upper Khuff outcrop equivalent (KS1)]. The Lower Mahil Formation was deposited on a carbonate ramp in Al Jabal al-Akhdar of North Oman. Saiq Plateau and Wadi Sahtan sections of the Lower Mahil Formation were logged and measured along a depositional dip cross section. A detailed sedimentological description for studied sections was performed using Dunham’s classification, isotope samples were taken every 50 cm, and spectral gamma ray measurements were taken every 10 cm. The Lower Mahil Formation is a third-order sequence consisting of inner-ramp and mid-ramp carbonate facies. Several lithofacies were identified, including breccia, packstone/grainstone, and mudstone. The top of the breccia marks the top of the third-order sequence with normal carbon isotope and low gamma rays and shows a sharp change in lithology. However, the base of this sequence is a transition contact with a gradual decrease in the carbon isotope and gamma ray curves. An increasing trend of both carbon isotope and gamma ray curves marks the maximum flooding surface zone.