The radiocarbon isotope data of aragonite, calcite, and dolomite veins and whole-rock total inorganic carbon and total non-carbonate carbon from ultramafic and mafic rocks recovered during ICDP Expedition 5057, Oman Drilling Project Phase II (November 2017 to February 2018) on the Wadi Tayin Massif, Samail Ophiolite, was examined to characterize carbon sources, speciation, and the fate of organic and inorganic carbon during natural large-scale hydration and carbonization. The measurements were performed at the ETH Zurich from 2017 to 2020 using an Elemental Analyzer interfaced to a MICADAS Accelerator Mass Spectrometer (AMS) equipped with a gas-ion source or by direct injection of CO2, from carbonate dissolution, into the ion source of the AMS. Analyzed whole-rock samples are aliquots of samples used for microbiological studies and were collected under sterile conditions (denoted as MBio samples).