Diagenetic perspectives from C–O–Sr isotopes in Early Cambrian carbonates: implications for reservoir evolution in the Buah Formation, Jabal Akhdar and Huqf regions, Oman

The Buah Formation, a key carbonate unit within the Huqf Supergroup of Oman, was deposited during the latest Ediacaran to early Cambrian (~ 541–530 Ma) and is well-exposed in the Jabal Akhdar (JA) and Huqf regions. These carbonates offer critical insights into early Cambrian diagenetic processes and serve as valuable records for geochemical and isotopic investigations. Samples from both regions were analyzed for carbon, oxygen, and strontium isotopes, along with elemental ratios using multiple mass spectrometry techniques. JA samples exhibit a broader and more variable range of δ¹³C and δ¹⁸O values compared to the more constrained values in Huqf, reflecting more extensive diagenetic overprinting. Positive δ¹³C–δ¹⁸O correlations in both regions indicate diagenetic alteration by meteoric and/or burial fluids. In the JA section, δ¹³C values as low as − 8‰ at lower stratigraphic levels likely result from the oxidation of Neoproterozoic organic carbon, releasing ¹²C-enriched DIC, a signature consistent with the Ediacaran Shuram excursion in the underlying Shuram Formation. Mn/Sr ratios distinguish diagenetic systems, with burial diagenesis and/or organic carbon oxidation dominating in JA, and meteoric diagenesis prevailing in Huqf. Strontium concentrations in Huqf samples range from 20 to 2600 ppm, with most exhibiting uniform ⁸⁷Sr/⁸⁶Sr ratios (~ 0.7088), outside typical marine dolomite values. A subset aligns with marine signatures, suggesting mixed Sr sources including terrigenous, hydrothermal, and weathering-derived inputs. Two δ¹³C-based sample populations (< 0.5‰ and ≥ 0.5‰) in Huqf highlight diagenetic variability with implications for reservoir quality, fluid migration, and source preservation in early Cambrian petroleum systems in Oman.