This dataset contains oxygen and carbon isotope data of the shells of A. benedeni benedeni specimens SG-126 and SG-127, as well as two in-house standards (Naxos, Kiel-carbonate). These measurements were carried out in order to establish a sclerochronological record of year-by-year shell growth. The bivalve shells were collected in 2013 from a shell bed at the top of the Oorderen Member of the Lillo Formation of the Pliocene in Belgium. The collection site was a construction-related temporary outcrop at the Deurganck Dock Lock (now Kieldrecht Lock) in the city of Antwerp, located at 51°16′44″N 4°14′52″E. Oxygen and carbon stable isotopes were measured in spring 2021 at the department of Earth Sciences at Utrecht University, the Netherlands, on a Thermo Scientific GasBench II gas preparation system coupled to a Thermo Scientific MAT 253 isotope ratio mass spectrometer and using a LIDI workflow. The dataset includes raw data and corrected values, and final values are reported relative to the Vienna Pee-Dee Belemnite (VPDB) standard.